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Journal Cover Journal of Ecology
  [SJR: 4.01]   [H-I: 131]   [138 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0022-0477 - ISSN (Online) 1365-2745
   Published by John Wiley and Sons Homepage  [1579 journals]
  • Effects of crown architecture and stand structure on light absorption in
           mixed and monospecific Fagus sylvatica and Pinus sylvestris forests along
           a productivity and climate gradient through Europe
    • Authors: D. I. Forrester; Ch. Ammer, P. J. Annighöfer, I. Barbeito, K. Bielak, A. Bravo-Oviedo, L. Coll, M. del Río, L. Drössler, M. Heym, V. Hurt, M. Löf, J. den Ouden, M. Pach, M. G. Pereira, B. N. E. Plaga, Q. Ponette, J. Skrzyszewski, H. Sterba, M. Svoboda, T. Zlatanov, H. Pretzsch
      Abstract: 1.When tree-species mixtures are more productive than monocultures, higher light absorption is often suggested as a cause. However, few studies have quantified this effect and even fewer have examined which light-related interactions are most important, such as the effects of species interactions on tree allometric relationships and crown architecture, differences in vertical or horizontal canopy structure, phenology of deciduous species or the mixing effects on tree size and stand density.2.In this study, measurements of tree sizes and stand structures were combined with a detailed tree-level light model (Maestra) to examine the contribution of each light-related interaction on tree- and stand-level light absorption at 21 sites, each of which contained a triplet of plots including a mixture and monocultures of Fagus sylvatica and Pinus sylvestris (63 plots). These sites were distributed across the current distribution of these species within Europe.3.Averaged across all sites, the light absorption of mixtures was 14% higher than the mean of the monocultures. At the whole community level, this positive effect of mixing on light absorption increased as canopy volume or site productivity increased, but was unrelated to climate. At the species population or individual tree levels, the mixing effect on light absorption resulted from light-related interactions involving vertical canopy structure, stand density, the presence of a deciduous species (F. sylvatica), as well as the effects of mixing on tree size and allometric relationships between diameter and height, crown diameter and crown length.4.The mixing effects on light absorption were only correlated with the mixing effects on growth for P. sylvestris, suggesting that the mixing effects on this species were driven by the light-related interactions, whereas mixing effects on F. sylvatica or whole community growth were probably driven by non-light-related interactions.5.Synthesis. The overall positive effect of mixing on light absorption was the result of a range of light-related interactions. However, the relative importance of these interactions varied between sites and is likely to vary between other species combinations and as stands develop.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-29T05:08:03.041176-05:
      DOI: 10.1111/1365-2745.12803
       
  • Habitat filtering determines the functional niche occupancy of plant
           communities worldwide
    • Authors: Yuanzhi Li; Bill Shipley, Jodi N. Price, Vinícius L. Dantas, Riin Tamme, Mark Westoby, Andrew Siefert, Brandon S. Schamp, Marko J. Spasojevic, Vincent Jung, Daniel C. Laughlin, Sarah J. Richardson, Yoann Le Bagousse-Pinguet, Christian Schöb, Antonio Gazol, Honor C. Prentice, Nicolas Gross, Jake Overton, Marcus V. Cianciaruso, Frédérique Louault, Chiho Kamiyama, Tohru Nakashizuka, Kouki Hikosaka, Takehiro Sasaki, Masatoshi Katabuchi, Cédric Frenette Dussault, Stephanie Gaucherand, Ning Chen, Marie Vandewalle, Marco Antônio Batalha
      Abstract: 1.How the patterns of niche occupancy vary from species-poor to species-rich communities is a fundamental question in ecology that has a central bearing on the processes that drive patterns of biodiversity. As species richness increases, habitat filtering should constrain the expansion of total niche volume, while limiting similarity should restrict the degree of niche overlap between species. Here, by explicitly incorporating intraspecific trait variability, we investigate the relationship between functional niche occupancy and species richness at the global scale.2.We assembled 21 datasets worldwide, spanning tropical to temperate biomes and consisting of 313 plant communities representing different growth forms. We quantified three key niche occupancy components (the total functional volume, the functional overlap between species and the average functional volume per species) for each community, related each component to species richness, and compared each component to the null expectations.3.As species richness increased, communities were more functionally diverse (an increase in total functional volume), and species overlapped more within the community (an increase in functional overlap) but did not more finely divide the functional space (no decline in average functional volume). Null model analyses provided evidence for habitat filtering (smaller total functional volume than expectation), but not for limiting similarity (larger functional overlap and larger average functional volume than expectation) as a process driving the pattern of functional niche occupancy.4.Synthesis. Habitat filtering is a widespread process driving the pattern of functional niche occupancy across plant communities and coexisting species tend to be more functionally similar rather than more functionally specialized. Our results indicate that including intraspecific trait variability will contribute to a better understanding of the processes driving patterns of functional niche occupancy.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-27T18:36:52.863447-05:
      DOI: 10.1111/1365-2745.12802
       
  • Improving spatial predictions of taxonomic, functional and phylogenetic
           diversity
    • Authors: Manuela D'Amen; Rubén G. Mateo, Julien Pottier, Wilfried Thuiller, Luigi Maiorano, Loïc Pellissier, Charlotte Ndiribe, Nicolas Salamin, Antoine Guisan
      Abstract: 1.In this study, we compare two community modelling approaches to determine their ability to predict the taxonomic, functional and phylogenetic properties of plant assemblages along a broad elevation gradient and at a fine resolution. The first method is the standard stacking individual species distribution modelling (SSDM) approach, which applies a simple environmental filter to predict species assemblages. The second method couples the SSDM and macroecological modelling (MEM - SSDM-MEM) approaches to impose a limit on the number of species co-occurring at each site. Because the detection of diversity patterns can be influenced by different levels of phylogenetic or functional trees, we also examine whether performing our analyses from broad to more exact structures in the trees influences the performance of the two modelling approaches when calculating diversity indices.2.We found that coupling the SSDM with the MEM improves the overall predictions for the three diversity facets compared with those of the SSDM alone. The accuracy of the SSDM predictions for the diversity indices varied greatly along the elevation gradient, and when considering broad to more exact structure in the functional and phylogenetic trees, the SSDM-MEM predictions were more stable.3.SSDM-MEM moderately but significantly improved the prediction of taxonomic diversity, which was mainly driven by the corrected number of predicted species. The performance of both modelling frameworks increased when predicting the functional and phylogenetic diversity indices. In particular, fair predictions of the taxonomic composition by SSDM-MEM led to increasingly accurate predictions of the functional and phylogenetic indices, suggesting that the compositional errors were associated with species that were functionally or phylogenetically close to the correct ones; however, this did not always hold for the SSDM predictions.4.Synthesis. In this study, we tested the use of a recently published approach that couples species distribution and macroecological models to provide the first predictions of the distribution of multiple facets of plant diversity: taxonomic, functional and phylogenetic. Moderate but significant improvements were obtained; thus, our results open promising avenues for improving our ability to predict the different facets of biodiversity in space and time across broad environmental gradients when functional and phylogenetic information is available.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-26T10:30:45.959686-05:
      DOI: 10.1111/1365-2745.12801
       
  • Root morphology and mycorrhizal type strongly influence root production in
           nutrient hot spots of mixed forests
    • Authors: Weile Chen; Roger T. Koide, David M. Eissenstat
      Abstract: 1.Plants compete for nutrients using a range of strategies. We investigated nutrient foraging within nutrient hot-spots simultaneously available to plant species with diverse root traits. We hypothesized that there would be more root proliferation by thin-root species than by thick-root species, and that root proliferation by thin-root species would limit root proliferation by thick-root species.2.We conducted a root ingrowth experiment in a temperate forest in eastern USA where root systems of different tree species could interact. Tree species varied in the thickness of their absorptive roots, and were associated with either ectomycorrhizal (EM) or arbuscular mycorrhizal (AM) fungi. Thus, there were thin- and thick-root AM and thin- and thick-root EM plant functional groups. Half the ingrowth cores were amended with organic nutrients (dried green leaves). Relative root length abundance, the proportion of total root length in a given soil volume occupied by a particular plant functional group, was calculated for the original root population and ingrowth roots after 6 months.3.The shift in relative root length abundance from original to ingrowth roots was positive in thin-root species but negative in thick-root species (P < 0.001), especially in unamended patches (AM: +6% vs. -7%; EM: +8% vs. -9%). Being thin-rooted may thus allow a species to more rapidly recolonize soil after a disturbance, which may influence competition for nutrients. Moreover, we observed that nutrient additions amplified the shift in root length abundance of thin over thick roots in AM trees (+13% vs. -14%), but not in EM trees (+1% vs -3%). In contrast, phospholipid fatty acid biomarkers suggested that EM fungal hyphae strongly proliferated in nutrient hot-spots whereas AM fungal hyphae exhibited only modest proliferation.4.We found no evidence that when growing in the shared patch, the proliferation of thin roots inhibited the growth of thick roots.5.Synthesis. Knowledge of root morphology and mycorrhizal type of co-existing tree species may improve prediction of patch exploitation and nutrient acquisition in heterogeneous soils.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-26T09:45:35.779908-05:
      DOI: 10.1111/1365-2745.12800
       
  • The role of changing climate in driving the shift from perennial grasses
           to annual succulents in a Mediterranean salt marsh
    • Authors: Elisabeth M.A. Strain; Jim Belzen, Paolo Comandini, Joanne Wong, Tjeerd J. Bouma, Laura Airoldi
      Abstract: 1.Changing climate threatens the structure and function of salt marshes, which are often severely degraded by other human perturbations. Along the Mediterranean coastline, increasing temperature and decreasing rainfall have been hypothesised to trigger habitat shifts from perennial grasses to annual succulents in fragile salt marsh ecosystems, such as those fringing the North Adriatic coastline.2.We used manipulative field experiments to investigate the effects of increased temperature, decreased precipitation and increased inundation period associated with rising sea levels on the dominant species in the lower marsh, the perennial grass Spartina spp. and the annual succulent Salicornia veneta.3.At ambient inundation, the combined effects of increased temperature and decreased precipitation enhanced soil temperature and decreased soil moisture, resulting in an increased number of plants, height and live biomass of S. veneta, as well as greater dead biomass of Spartina spp. compared with current conditions. Increased inundation reduced the soil redox potential, and resulted in losses of both Spartina spp. and S. veneta, but these negative effects were much more pronounced for S. veneta. An inundation tolerance test confirmed that S. veneta is significantly more vulnerable to rapid increases in inundation than Spartina spp..4.We conclude that at current inundation, the increasing drought conditions in the North Adriatic Sea are favouring the spread of the annual succulent S. veneta. The increasing spread of these succulents could reduce the future capability of the system to respond to projected increasing sea levels, as S. veneta is highly vulnerable to increased inundation.5.Synthesis – Our results highlight the complex interactions between different components of changing climate. Management strategies for salt marshes in the Mediterranean and other micro-tidal locations facing similar changes in climate should focus on maintaining the freshwater and coastal channels free from blockages to ameliorate the effects of episodic drought/heatwave conditions and increasing the sediment supply and preventing coastal squeeze to enhance the resilience of the system to the continuous threat of sea-level rise.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-24T08:00:42.647169-05:
      DOI: 10.1111/1365-2745.12799
       
  • The effects of climate warming and disturbance on the colonization
           potential of ornamental alien plant species
    • Authors: Emily Haeuser; Wayne Dawson, Mark Kleunen
      Abstract: 1.A large number of alien plant species have been introduced as ornamental garden plants to Europe, but relatively few have become invasive. Low climatic suitability may be limiting the current invasion potential of many alien ornamental species. However, with ongoing disturbance and climate change, this barrier may be reduced for some species.2.Here we tested how colonization ability (a prerequisite for invasion) of frequently planted alien ornamentals depends on disturbance and heating, and on their species characteristics. We sowed seeds of 37 non-naturalized alien herbaceous garden-plant species into native grassland plots with and without disturbance, and with and without infrared heating lamps. To assess whether their responses differ from those within the regional wild flora, we also sowed 14 native species and 12 naturalized alien species. During two years, we assessed the likelihoods of germination, first-year survival, second-year survival and flowering of these 63 study species.3.The heating treatment, which also reduced soil moisture, decreased all measures of colonization success, but more so for sown native species than for the non-naturalized and naturalized alien ones. The disturbance treatment increased colonization success, and because heating decreased productivity of the undisturbed grassland plots, it also increased invasibility of these plots. Average colonization success of non-naturalized aliens was reduced by heating, but some species were not affected or performed even better with heating, particularly those with an annual life span and a high seed mass. Winter hardiness improved colonization ability of non-naturalized aliens, but this advantage was reduced in the heated plots.4.Synthesis. Disturbance increased and heating decreased the absolute colonization success of most of the 63 species sown. However, heating had stronger adverse effects on the resident grassland and sown native species than either type of sown alien species. Together, these results suggest that some alien plants may have greater colonization success relative to native plants under a warmer climate.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-24T08:00:32.525083-05:
      DOI: 10.1111/1365-2745.12798
       
  • Biological Flora of the British Isles: Phragmites australis
    • Authors: Jasmin G. Packer; Laura A. Meyerson, Hana Skálová, Petr Pyšek, Christoph Kueffer
      Abstract: 1.This account presents comprehensive information on the biology of Phragmites australis (Cav.) Trin. ex Steud. (P. communis Trin.; common reed) that is relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors and to the abiotic environment, plant structure and physiology, phenology, floral and seed characters, herbivores and diseases, as well as history including invasive spread in other regions, and conservation.2.Phragmites australis is a cosmopolitan species native to the British flora and widespread in lowland habitats throughout, from the Shetland archipelago to southern England. It is widespread throughout Ireland and is native in the Channel Islands. Native populations occur naturally in temperate zones and on every continent except Antarctica. Some populations in Australia and North America have been introduced from elsewhere and have become naturalized, and in North America some of these are known to be invasive where they compete with native local populations of P. australis. Typical habitats in Britain range from shallow still water along waterbody edges to marshlands, salt marshes and drier habitat on slopes up to 470 m above sea level. Additional habitats outside Britain are springs in arid areas (-5 m above sea level) and groundwater seepage points up to 3600 m above sea level. Although it occurs on a wide range of substrates and can tolerate pH from 2.5 to 9.8, in Britain it prefers pH >4.5 and elsewhere it thrives in mildly acidic to mildly basic conditions (pH 5.5–7.5). The species plays a pivotal role in the successional transition from open water to woodland.3.Phragmites australis is a tall, helophytic, wind-pollinated grass with annual shoots up to 5 m above ground level from an extensive system of rhizomes and stolons. A single silky inflorescence develops at the end of each fertile stem and produces 500–2000 seeds. The plant is highly variable genetically and morphologically.4.Expansion of established populations is mainly through clonal growth of the horizontal rhizome system and ground-surface stolons, while new populations can establish from rhizomes, stem fragments and seeds. Shoots generally emerge in spring, with timing determined primarily by physiology that is mediated by external conditions (e.g. local climate including frost).5.Many populations in the British Isles have experienced some decline over the past two decades and there is concern that there might be further losses along the east coast as sea level rises. There has recently also been localized expansions, especially in highly modified habitats: where P. australis reedbeds have been planted as wildlife habitat, rehabilitated mineral- and gravel-beds, and bioremediation filter beds for industrial and transport infrastructure. Native populations outside Britain also demonstrate both types of trends: they are declining in many parts of Western Europe and North America, yet also colonise many disturbed, ruderal habitats (e.g. the edges of agricultural fields and motorways) throughout its native and non-native range and can form ‘weedy’ monodominant populations (e.g. in Australia and China).This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-24T00:35:39.123421-05:
      DOI: 10.1111/1365-2745.12797
       
  • Effects of biological legacies and herbivory on fuels and flammability
           traits: A long-term experimental study of alternative stable states
    • Authors: Melisa Blackhall; Estela Raffaele, Juan Paritsis, Florencia Tiribelli, Juan M. Morales, Thomas Kitzberger, Juan H. Gowda, Thomas T. Veblen
      Abstract: 1.Ecological memory, often determined by the extent and type of retained biological legacies present following disturbance, may produce persistent landscape patterns. However, after fire, the persistence or switch to an alternative state may depend on the complex interplay of ecological memory (biological legacies) and potential effects of new external factors influencing the post-fire environment. The current study assesses both the strength of ecological memory resulting from biological legacies of pre-burn vegetation types as well as post-fire effects of livestock.2.Following a severe fire in 1999, we set up a network of long-term exclosures to examine the effects of legacies and cumulative herbivory by cattle on fuel types, amounts, distribution, flammability and micro-environmental conditions in two post-fire communities representing alternative fire-driven states: pyrophobic Nothofagus pumilio subalpine forests and pyrophytic N. antarctica tall shrublands in northwestern Patagonia, Argentina.3.Our results show that the retained post-disturbance legacies of tall shrublands and subalpine forests largely determine fuel and flammability traits of the post-fire plant communities 16 years after fire. The importance of biological legacies retained from the unburned plant communities was reflected by the substantially higher amounts of total fine fuel, greater vertical and horizontal fuel continuity and the higher temperatures reached during experimental tissue combustion at post-fire shrubland compared to post-fire forest sites.4.We show that herbivores may produce antagonistic effects on flammability by decreasing tissue ignitability, total fine fuel and litter depth, and disrupting the vertical and horizontal fine fuel continuity, therefore reducing the probability of fire propagation. However, cattle can increase ratios of dead to live fine fuels, reduce soil moisture, and inhibit tree height growth to canopy size, consequently impeding the development of a closed pyrophobic forest canopy.5- Synthesis. Our results support the hypothesis that biological legacies, most importantly the dominance by pyrophytic woody plants that resprout vigorously versus the dominance by pyrophobic obligate seeders, favour fuel and flammability characteristics at the community level which reinforce the mechanisms maintaining pyrophytic shrublands versus pyrophobic forests. Herbivory by introduced cattle can partially blur sharp pyrophobic/pyrophytic state boundaries by promoting the development of novel post-fire transitional states.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-19T13:03:11.32632-05:0
      DOI: 10.1111/1365-2745.12796
       
  • Logging increases the functional and phylogenetic dispersion of
           understorey plant communities in tropical lowland rainforest
    • Authors: Timm F. Döbert; Bruce L. Webber, John B. Sugau, Katharine J.M. Dickinson, Raphael K. Didham
      Abstract: 1. Logging is a major driver of tropical forest degradation, with severe impacts on plant richness and composition. Rarely have these effects been considered in terms of their impact on the functional and phylogenetic diversity of understorey plant communities, despite the direct relevance to community reassembly trajectories. Here, we test the effects of logging on functional traits and evolutionary relatedness, over and above effects that can be explained by changes in species richness alone. We hypothesised that strong environmental filtering will result in more clustered (under-dispersed) functional and phylogenetic structures within communities as logging intensity increases.2. We surveyed understorey plant communities at 180 locations across a logging intensity gradient from primary to repeatedly-logged tropical lowland rainforest in Sabah, Malaysia. For the 691 recorded plant taxa, we generated a phylogeny to assess plot-level phylogenetic relatedness. We quantified 10 plant traits known to respond to disturbance and affect ecosystem functioning, and tested the influence of logging on functional and phylogenetic structure.3. We found no significant effect of forest canopy loss or road configuration on species richness. By contrast, both functional dispersion (FDis) and phylogenetic dispersion (net relatedness index, NRI) showed strong gradients from clustered towards more randomly-assembled communities at higher logging intensity, independent of variation in species richness. Moreover, there was a significant non-linear shift in the trait dispersion relationship above a logging intensity threshold of ca. 65% canopy loss (± 17% CL). All functional traits showed significant phylogenetic signals, suggesting broad concordance between functional and phylogenetic dispersion, at least below the logging intensity threshold.4. Synthesis. We found a strong logging signal in the functional and phylogenetic structure of understorey plant communities, over and above species richness, but this effect was opposite to that predicted. Logging increased, rather than decreased, functional and phylogenetic dispersion in understorey plant communities. This effect was particularly pronounced for functional response traits, which directly link disturbance with plant community reassembly. Our study provides novel insights into the way logging affects understorey plant communities in tropical rainforest and highlights the importance of trait-based approaches to improve our understanding of the broad range of logging-associated impacts.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-19T12:59:39.095784-05:
      DOI: 10.1111/1365-2745.12794
       
  • Root and shoot glucosinolate allocation patterns follow optimal defence
           allocation theory
    • Authors: Tomonori Tsunoda; Sebastian Krosse, Nicole M. van Dam
      Abstract: Optimal defence allocation theory (ODT) is one of the most prominent theoretical frameworks to explain the allocation of defence compounds within plants. It predicts that the most valuable and vulnerable plant organs have the highest levels of chemical defence. The ODT has been well worked out and experimentally tested for shoot defences, but not for root defences. To assess if ODT principles apply similarly to roots and shoots, we examined glucosinolates in aboveground and belowground organs of nine plant species belonging to two families.In order to evaluate whether ODT equally applies to shoot and root organs, we designed a conceptual model in which aboveground and belowground organs were assigned to orders of importance to plant performance. We hypothesized that organs constituting the plant's core structure are better protected than more distal organs.The nine plant species were cultivated, and their roots and shoots were harvested and divided in three orders for glucosinolate analysis. Using a specialist (Delia radicum) and a generalist (Amphimallon solstitiale) root herbivore, we also experimentally tested the hypothesis that the generalist herbivore prefers to feed on fine roots with a low glucosinolate concentration, while the specialist prefers taproots with a high glucosinolate concentration.We found that both in roots and shoots the higher-ordered core structural organs (taproots and stems) had the highest levels of glucosinolates. Belowground, taproots and lateral roots were better protected than the more distal, and less costly, fine roots in seven out of nine species tested. The specialist root herbivore preferred feeding on the highly defended taproots, which is in line with what has been found for aboveground specialist herbivores. Moreover, the glucosinolate concentration in roots overall was significantly higher than that in shoots.Synthesis. These results support the hypothesis that ODT generally applies to glucosinolate allocation in aboveground and belowground organs and may mainly serve to maintain the integrity of the main plant structure. Moreover, it suggests that aboveground and belowground insect herbivores independently exert similar selection pressures on defence allocation patterns in roots and shoots.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-18T12:43:52.317437-05:
      DOI: 10.1111/1365-2745.12793
       
  • Climate and competition effects on tree growth in Rocky Mountain forests
    • Authors: Arne Buechling; Patrick H. Martin, Charles D. Canham
      Abstract: 1.Climate is widely assumed to influence physiological and demographic processes in trees, and hence forest composition, biomass and range limits. Growth in trees is an important barometer of climate change impacts on forests as growth is highly correlated with other demographic processes including tree mortality and fecundity.2.We investigated the main drivers of diameter growth for five common tree species occurring in the Rocky Mountains of the western United States using non-linear regression methods. We quantified growth at the individual tree level from tree core samples collected across broad environmental gradients. We estimated the effects of both climate variation and biotic interactions on growth processes and tested for evidence that disjunct populations of a species respond differentially to climate.3.Relationships between tree growth and climate varied by species and location. Growth in all species responded positively to increases in annual moisture up to a threshold level. Modest linear responses to temperature, both positive and negative, were observed at many sites. However, model results also revealed evidence for differentiated responses to local site conditions in all species. In severe environments in particular, growth responses varied non-linearly with temperature. For example, in northerly cold locations pronounced positive growth responses to increasing temperatures were observed. In warmer southerly climates, growth responses were unimodal, declining markedly above a threshold temperature level.4.Net effects from biotic interactions on diameter growth were negative for all study species. Evidence for facilitative effects was not detected. For some species, competitive effects more strongly influenced growth performance than climate. Competitive interactions also modified growth responses to climate to some degree.6.Synthesis. These analyses suggest that climate change will have complex, species specific effects on tree growth in the Rocky Mountains due to non-linear responses to climate, differentiated growth processes that vary by location and complex species interactions that impact growth and potentially modify responses to climate. Thus, robust model simulations of future growth responses to climate trends may need to integrate realistic scenarios of neighborhood effects as well as variability in tree performance attributed to differentiated populations.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-12T04:25:55.00461-05:0
      DOI: 10.1111/1365-2745.12782
       
  • Multi-scale drivers of community diversity and composition across tidal
           heights: an example on temperate seaweed communities
    • Authors: Marine Robuchon; Myriam Valero, Eric Thiébaut, Line Le Gall
      Abstract: 1.Despite recent advances in understanding community assembly processes, appreciating how these processes vary across multiple spatial scales and environmental gradients remains a crucial issue in ecology.2.This study aimed to disentangle the drivers of diversity and composition of seaweed communities through a gradient of spatial scales based on a hierarchical sampling design consisting of 19 sites distributed in four sectors along the Brittany coastline. Using randomised community matrices and Moran's eigenvector maps (MEMs), we compared i) the relative importance of deterministic and stochastic processes, ii) the environmental correlates of community composition and iii) the scale of variation in community composition for seaweed communities located at two different tidal heights.3.Processes shaping community patterns are expected to vary along a gradient of tidal heights. Therefore, we specifically examined the following hypotheses: the contribution of deterministic over stochastic processes as well as the relative importance of environmental filtering over biotic interactions should be enhanced for seaweed communities of the infralittoral fringe compared to subtidal ones, whereas dispersal of propagules in the water column should be more restricted resulting in finer-scale variation in community composition for seaweed communities of the infralittoral fringe compared to subtidal communities.4.Seaweed communities were largely shaped by deterministic processes, although the relative importance of deterministic processes was greater for communities of the infralittoral fringe than for subtidal communities. Sea surface temperature and geophysical variables were correlates of community composition at the two tidal heights; additionally, waves and current were correlated with the composition of the communities of the infralittoral fringe while kelp density was correlated with the composition of subtidal communities. Variation in community composition was observed at a finer scale for infralittoral fringe than for subtidal communities.Synthesis. Our results suggest that the relative importance of deterministic and stochastic processes in structuring seaweed communities varies across tidal heights. Furthermore, the MEMs framework highlights that the nature of environmental correlates and the spatial scale at which they were good correlates of community composition also vary across tidal heights and may therefore be useful to broaden our understanding of community assembly across vertical gradients.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-09T23:55:25.836747-05:
      DOI: 10.1111/1365-2745.12781
       
  • Interactions between rainfall, fire and herbivory drive resprouter vital
           rates in a semi-arid ecosystem
    • Authors: Katherine M. Giljohann; Michael A. McCarthy, David A. Keith, Luke T. Kelly, Mark G. Tozer, Tracey J. Regan
      Abstract: Global change is threatening ecosystems and biodiversity world-wide, creating a pressing need to understand how climate and disturbance regimes interact and influence the persistence of species. We quantify how three ecosystem drivers – rainfall, fire and herbivory – influence vital rates in the perennial resprouting graminoid, Triodia scariosa, a foundation species of semi-arid Australia.We used an 11-year dataset from a fire and herbivore exclosure experiment, to model flowering, post-fire recruitment and the post-fire survival of seedlings and resprouting plants. Regression modelling quantified the effect of rainfall, inter-fire interval, fire type (wildfire or prescribed fire), grazing by herbivores (native and feral) and an interaction between fire type and herbivory on T. scariosa populations.Rainfall, fire and herbivory had significant effects on post-fire recruitment and the survival of seedlings and resprouting plants, including strong interactions between these drivers. Herbivory following wildfire had a minor effect, but in years of below-average rainfall herbivory following prescribed fire had a large effect, reducing the survival of seedlings and resprouting plants by 20% and over 50% respectively, relative to post-fire survival under average rainfall conditions.Variation in rainfall underpinned significant variation in post-fire resprouting and seedling survival, thus we postulate rainfall primarily drives the dynamics of T. scariosa populations.Synthesis. This study highlights the importance of modelling interactions between key ecosystem drivers when predicting how changes in global climate and disturbance regimes influence plant vital rates. Relatively small changes to disturbance regimes can substantially alter population processes, even in perennial resprouting species. This work suggests that conservation of foundation species, such as T. scariosa, will benefit if fire management decisions are better integrated with inter-annual weather forecasts and herbivore management.Our study shows the importance of modelling interactions between key ecosystem drivers when predicting how changes in global climate and disturbance regimes influence plant vital rates. Relatively small changes to disturbance regimes substantially altered population processes in a perennial resprouting species. This suggests that conservation of foundation species will benefit if fire management decisions are better integrated with inter-annual weather forecasts and herbivore management. The photo was taken by David Keith at Tarawi Nature Reserve in 2013 and shows part of a herbivore exclosure at 7 years post-fire.
      PubDate: 2017-04-06T05:35:18.93946-05:0
      DOI: 10.1111/1365-2745.12768
       
  • Corrigendum
    • PubDate: 2017-04-06T05:35:06.352313-05:
      DOI: 10.1111/1365-2745.12776
       
  • The fate of nitrogen inputs in a warmer alpine treeline ecosystem: a 15N
           labelling study
    • Authors: Melissa A. Dawes; Patrick Schleppi, Frank Hagedorn
      Abstract: Global warming may accelerate nitrogen (N) transformations in the soil, with potentially large effects in N-poor high-elevation ecosystems. To gain insight into the partitioning of inorganic and organic N inputs within the plant-soil system and how warming influences these patterns, we applied a 15N label (15NH4Cl or 15N-glycine) shortly after snowmelt during the sixth year of experimental soil warming (+4°C) at treeline in the Swiss Alps.Seven weeks after labelling, approximately 60% of the applied label remained in the soil organic layer to 10 cm depth, whereas label recovery summed over all measured plant pools was
      PubDate: 2017-04-04T15:55:23.148449-05:
      DOI: 10.1111/1365-2745.12780
       
  • Microbial communities in soil chronosequences with distinct parent
           material: the effect of soil pH and litter quality
    • Authors: Fernando D. Alfaro; Marlene Manzano, Pablo A. Marquet, Aurora Gaxiola
      Abstract: During soil development, bacteria and fungi can be differentially affected by changes in soil biogeochemistry. Since the chemistry of parent material affects soil pH, nutrient availability, and indirectly litter quality, we hypothesize that parent material has an important influence on microbial community patterns during long-term soil development.In this paper, we tested for the effect of parent material, as well as, soil and litter properties upon microbial community patterns in three c. 20 000-year-old semi-arid chronosequences developed on sedimentary and volcanic (i.e. Andesitic and Dacitic) soils in the Dry Puna of Bolivia. We evaluated microbial patterns by analysing the terminal restriction fragment length polymorphism from amplified bacterial 16S rRNA genes, and the fungal internal transcribed spacer region, and quantitative real-time polymerase chain reaction.Soil and litter characteristics differed significantly between the Sedimentary and volcanic chronosequences. In particular, soil pH was alkaline in all stages of the Sedimentary chronosequence; whereas it changed from alkaline to near neutral across stages in both volcanic chronosequences. Composition of bacterial communities changed across volcanic chronosequences, and this change was associated with a reduction in soil pH and increases in litter quality, whereas no differences were found in the Sedimentary chronosequence. Fungal community composition, in contrast, did not change across any chronosequence.Relative microbial abundance, expressed as the fungal:bacterial ratio, declined across stages of the Sedimentary chronosequence in association with decreases in TC and TP, whereas in the Andesitic chronosequence decreases in fungal:bacterial ratios were related with increases in litter quality and declines in soil pH.Synthesis. Our results show the importance of parent material in affecting bacterial and fungal communities during soil development. Further, in semi-arid chronosequences, fungal:bacterial ratios tend to decline given that soil pH in young soils is rather alkaline. Our results also are consistent with the general framework that highlights the importance of above-ground (i.e. litter quality) and below-ground (i.e. soil properties) in affecting microbial relative abundance and community composition during soil development.We tested the effect of parent material, as well as soil and litter properties, upon microbial community patterns in c. 20 000-year-old chronosequences of sedimentary and volcanic origin in the Dry Puna of Bolivia. We show that parent material is paramount in affecting soil pedogenesis and ecosystem dynamics via its effects upon soil pH, soil nutrient availability and litter quality, which in turn affects microbial abundance and composition.
      PubDate: 2017-04-04T03:45:59.613721-05:
      DOI: 10.1111/1365-2745.12766
       
  • Soil carbon response to woody plant encroachment: importance of spatial
           heterogeneity and deep soil storage
    • Authors: Yong Zhou; Thomas W. Boutton, X. Ben Wu
      Abstract: Recent global trends of increasing woody plant abundance in grass-dominated ecosystems may substantially enhance soil organic carbon (SOC) storage and could represent a strong carbon (C) sink in the terrestrial environment. However, few studies have quantitatively addressed the influence of spatial heterogeneity of vegetation and soil properties on SOC storage at the landscape scale. In addition, most studies assessing SOC response to woody encroachment consider only surface soils, and have not explicitly assessed the extent to which deeper portions of the soil profile may be sequestering C.We quantified the direction, magnitude and pattern of spatial heterogeneity of SOC in the upper 1·2 m of the profile following woody encroachment via spatially specific intensive soil sampling across a landscape in a subtropical savanna in the Rio Grande Plains, USA, that has undergone woody proliferation during the past century.Increased SOC accumulation following woody encroachment was observed to considerable depth, albeit at reduced magnitudes in deeper portions of the profile. Overall, woody clusters and groves accumulated 12·87 and 18·67 Mg C ha−1 more SOC compared to grasslands to a depth of 1·2 m.Woody encroachment significantly altered the pattern of spatial heterogeneity of SOC to a depth of 5 cm, with marginal effect at 5–15 cm, and no significant impact on soils below 15 cm. Fine root density explained greater variability of SOC in the upper 15 cm, while a combination of fine root density and soil clay content accounted for more of the variation in SOC in soils below 15 cm across this landscape.Synthesis. Substantial soil organic carbon sequestration can occur in deeper portions of the soil profile following woody encroachment. Furthermore, vegetation patterns and soil properties influenced the spatial heterogeneity and uncertainty of soil organic carbon in this landscape, highlighting the need for spatially specific sampling that can characterize this variability and enable scaling and modelling. Given the geographic extent of woody encroachment on a global scale, this undocumented deep soil carbon sequestration suggests this vegetation change may play a more significant role in regional and global carbon sequestration than previously thought.Woody plant encroachment into grasslands increased soil organic carbon (SOC) storage and influenced the spatial heterogeneity and uncertainty of SOC throughout the soil profile. In addition, much of the SOC accrual following woody encroachment was stored deep in the profile. Given the geographic extent of woody encroachment on a global scale, this undocumented deep soil C sequestration suggests this vegetation change may play a more significant role in regional and global C sequestration than previously thought.
      PubDate: 2017-04-03T07:50:44.37563-05:0
      DOI: 10.1111/1365-2745.12770
       
  • From pristine forests to high-altitude pastures: an ecological approach to
           prehistoric human impact on vegetation and landscapes in the western
           Italian Alps
    • Authors: Roberta Pini; Cesare Ravazzi, Luca Raiteri, Antonio Guerreschi, Lorenzo Castellano, Roberto Comolli
      Abstract: This paper addresses the origin and development of the oldest prehistoric pasture in the timberline ecotone known so far in the Alps and its relation to anthropogenic pressure and natural climate change.Palaeoecological and geochemical techniques were applied on the Crotte Basse mire stratigraphy (2365 m a.s.l, northwestern Italy) to describe changes in vegetation composition, forest biomass, land use and fertilization between c. 6400–1800 cal years bp.Subalpine forests dominated by Pinus cembra occurred at very high-altitude up to c. 5600 cal years bp, when a sharp contraction of woody vegetation took place. This major vegetation shift is matched by increasing charcoal input and markers of pastoral/grazing activities (pollen, dung spores and forms of phosphorus) in the sediment sequence in this small basin.Major phases of landscape change detected in our multiproxy record chronologically match intervals of cumulative probability density of 14C ages from nearby archaeological sites, suggesting that human activity was the factor leading to massive landscape change from the onset of the Copper Age (c. 5600 cal years bp). The change may have been reinforced by climate variability in the period 5700–5300 cal years bp.Sensitivity of woody species to fires was statistically explored (Appendix S1, Supporting Information), revealing negative reactions of P. cembra and Betula to frequent fire episodes and positive reactions of Alnus viridis and Juniperus. Fire episodes do not affect Larix dynamics.Synthesis. Mt. Fallère provides some of the oldest and consistent evidence so far available in the Alps for major anthropogenic pressure at the upper forest limit. As far back as 5600 cal years bp, high-elevation forest ecosystems were permanently disrupted and the alpine pastures were created. Palaeoecological data enable a clear distinction between a random and sporadic use of the alpine space, typical for Mesolithic and Neolithic societies, and an organized seasonal exploitation of natural resources, starting from the Copper Age onwards. The chronological comparison of independent climate proxies, palaeoecological information and pollen-based temperature reconstructions sheds light on the relationships between climate and humans since prehistoric times.This extensive and biodiverse cow pasture in the elevational belt of the western Italian Alps was suddenly installed at the Copper Age onset at the expenses of timberline forests. A 5600 years-long history of permanent herding and landscape management is narrated by the palaeoecological archive retrieved from a pond used for livestock watering.
      PubDate: 2017-04-03T02:31:18.828407-05:
      DOI: 10.1111/1365-2745.12767
       
  • Manipulating two olfactory cues causes a biological control beetle to
           shift to non-target plant species
    • Authors: Na Li; Shuang Li, Jin Ge, Meredith C. Schuman, Jia-Ning Wei, Rui-Yan Ma
      Abstract: 1.Olfactory cues can determine the host preferences of herbivorous insects, but their role in host shifting is unclear. Host specificity and the potential for host shifts are important criteria for screening and post-release evaluation of biological control agents for invasive plants. However, the role of olfactory cues in mediating host shifts in biological control agents is not well understood.2.To investigate the role of olfactory cues in host selection of a reportedly monophagous flea beetle (Agasicles hygrophila), an important biocontrol agent for invasive alligator weed (Alternanthera philoxeroides), we extracted and analyzed the volatiles produced by the host plant A. philoxeroides and the non-host plants A. sessilis, Beta vulgaris, and Amaranthus mangostanus. Moreover, we used electrophysiologcial techniques, behavioural bioassays and field trials to test the antennal responses and behavioural preferences of A. hygrophila to combinations of different plant volatiles and treatments, and pure compounds in different dosages and combinations.3.We show that A. hygrophila female beetles indeed use olfactory cues to select plants for feeding and oviposition and that the survivorship of larvae on the second preferred non-host plant A. sessilis, a close relative of the first preferred host plant A. philoxeroides, was over 75% in a field trail. Although female beetles responded to many volatile compounds from host and non-host plants, (E)-4,8-dimethyl-1,3,7- nonatriene (DMNT) positively encouraged the beetle's feeding and oviposition preferences, whereas (Z)-3-hexenol displayed repellent effect. Remarkably, complementation assays with (Z)-3-hexenol on host plant or DMNT on non-host plants significantly shifted A. hygrophila host preferences to non-host plants and resulted in oviposition and egg hatching on the non-host plant A. sessilis in field trials.4.Synthesis. We demonstrate an olfactory mechanism by which a specialized herbivorous beetle uses the ratio of two common plant volatiles, DMNT and (Z)-3-hexenol, to discriminate between its host and non-host plants in nature. This study highlights an important mechanism by which olfactory cues could lead to undesired host range expansion in biocontrol agent, thus representing an important warning of the potential for a host shift and development of invasiveness in a common biocontrol agent, the flea beetle.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-29T07:54:20.752819-05:
      DOI: 10.1111/1365-2745.12778
       
  • In the presence of specialist root and shoot herbivory, invasive-range
           Brassica nigra populations have stronger competitive effects than
           native-range populations
    • Authors: Ayub M.O. Oduor; Mark Kleunen, Marc Stift
      Abstract: 1.The evolution of increased competitive ability (EICA) hypothesis predicts that release from specialist herbivores enables invasive plants to evolve increased growth. The most powerful tests of EICA hypothesis are provided by approaches that simultaneously assess the effects of specialist herbivory and competitive interactions. However, such approaches are extremely rare, and hence how simultaneous release from root and shoot herbivory influence competitive ability of invasive plants remains little understood.2.Here, we tested whether invasive-range Brassica nigra plants have evolved increased competitive ability, and whether expression of competitive ability depends on separate and simultaneous effects of specialist root and shoot herbivory. To do this, we grew B. nigra plants from eight invasive-range and eight native-range populations in the presence versus absence of competition with a community of native plant species, and in the absence versus presence of separate and simultaneous damage by a specialist root herbivore (Delia radicum) and a specialist shoot herbivore (Plutella xylostella). Brassica nigra performance was assessed by measuring biomass production and flowering of individual B. nigra plants.3.In partial support of the EICA hypothesis, invasive-range B. nigra had greater flowering than native-range conspecifics in the absence of competition. However, contrary to a prediction of the EICA hypothesis, invasive-range B. nigra produced less aboveground biomass than native-range B.nigra in the absence of shoot herbivory and competition. Moreover, with simultaneous root and shoot herbivory, invasive-range B. nigra suppressed a competing community more strongly than native-range B. nigra did.4.Synthesis: Our results suggest that invasiveness may be driven by mechanisms other than increased individual size. Simultaneous root and shoot herbivory in the invasive range may enhance suppressive effects of introduced plant species that have not completely escaped herbivore damage in the introduced range.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-29T07:36:01.59134-05:0
      DOI: 10.1111/1365-2745.12779
       
  • Abiotic and biotic drivers of biomass change in a Neotropical forest
    • Authors: Masha T. Sande; Marielos Peña-Claros, Nataly Ascarrunz, Eric J. M. M. Arets, Juan Carlos Licona, Marisol Toledo, Lourens Poorter
      Abstract: Tropical forests play an important role in the global carbon cycle, but the drivers of net forest biomass change (i.e. net carbon sequestration) are poorly understood. Here, we evaluate how abiotic factors (soil conditions and disturbance) and biotic factors (forest structure, diversity and community trait composition) shape three important demographic processes (biomass recruitment, growth and mortality) and how these underlie net biomass change.To test this, we evaluated 9 years of biomass dynamics using 48 1-ha plots in a Bolivian tropical moist forest, and measured for the most abundant species eight functional traits that are important for plant carbon gain and loss. Demographic processes were related to the abiotic and biotic factors using structural equation models.Variation in net biomass change across plots was mostly due to stand-level mortality, but mortality itself could not be predicted at this scale. Contrary to expectations, we found that species richness and trait composition – which is an indicator for the mass-ratio theory – had little effect on the demographic processes. Biomass recruitment (i.e. the biomass growth by recruiting trees) increased with higher resource availability (i.e. water and light) and with high species richness, probably because of increased resource use efficiency. Biomass growth of larger, established trees increased with higher sand content, which may facilitate root growth of larger trees to deeper soil layers.In sum, diversity and mass-ratio are of limited importance for the productivity of this forest. Instead, in this moist tropical forest with a marked dry season, demographic processes are most strongly determined by soil texture, soil water availability and forest structure. Only by simultaneously evaluating multiple abiotic and biotic drivers of demographic processes, better insights can be gained into mechanisms playing a role in the carbon sequestration potential of tropical forests and natural systems in general.We evaluate how abiotic and biotic factors shape biomass recruitment, growth and mortality, and how these processes underlie net biomass change in a tropical forest. Net biomass change is mainly driven by mortality, but mortality is poorly predicted by abiotic and biotic factors. Productivity is determined by soil texture, soil water availability and forest structure, and not by diversity and mass-ratio.
      PubDate: 2017-03-27T10:20:28.951888-05:
      DOI: 10.1111/1365-2745.12756
       
  • Interspecific integration of trait dimensions at local scales: the plant
           phenotype as an integrated network
    • Authors: Julie Messier; Martin J. Lechowicz, Brian J. McGill, Cyrille Violle, Brian J. Enquist
      Abstract: Plant phenotypic diversity is shaped by the interplay of trade-offs and constraints in evolution. Closely integrated groups of traits (i.e. trait dimensions) are used to classify plant phenotypic diversity into plant strategies, but we do not know the degree of interdependence among trait dimensions. To assess how selection has shaped the phenotypic space, we examine whether trait dimensions are independent.We gathered data on saplings of 24 locally coexisting tree species in a temperate forest, and examined the correlation structure of 20 leaf, branch, stem and root traits. These traits fall into three well-established trait dimensions (the leaf economic spectrum, the wood spectrum and Corner's Rules) that characterize vital plant functions: resource acquisition, sap transport, mechanical support and canopy architecture. Using ordinations, network analyses and Mantel tests, we tested whether the sapling phenotype of these tree species is organized along independent trait dimensions.Across species, the sapling phenotype is not structured into clear trait dimensions. The trait relationships defining trait dimensions are either weak or absent and do not dominate the correlation structure of the sapling phenotype as a whole. Instead traits from the three commonly recognized trait dimensions are organized into an integrated trait network. The effect of phylogeny on trait correlations is minimal.Our results indicate that trait dimensions apparent in broad-based interspecific surveys do not hold up among locally coexisting species. Furthermore, architectural traits appear central to the phenotypic network, suggesting a pivotal role for branching architecture in linking resource acquisition, mechanical support and hydraulic functions.Synthesis. Our study indicates that local and global patterns of phenotypic integration differ and calls into question the use of trait dimensions at local scales. We propose that a network approach to assessing plant function more effectively reflects the multiple trade-offs and constraints shaping the phenotype in locally co-occurring species.Our study finds that globally defined trait dimensions are not independent (or even present) at a local scale. This calls into question the use of trait dimensions for local-scale ecology. We propose that a network approach to assessing plant function more effectively reflects the multiple trade-offs and constraints shaping the phenotype in locally co-occurring species.
      PubDate: 2017-03-27T05:12:15.333506-05:
      DOI: 10.1111/1365-2745.12755
       
  • Cross-scale interactions affect tree growth and intrinsic water use
           efficiency and highlight the importance of spatial context in managing
           forests under global change
    • Authors: Kenneth J. Ruzicka; Klaus J. Puettmann, J. Renée Brooks
      Abstract: We investigated the potential of cross-scale interactions to affect the outcome of density reduction in a large-scale silvicultural experiment to better understand options for managing forests under climate change.We measured tree growth and intrinsic water-use efficiency (iWUE) based on stable carbon isotopes (δ13C) to investigate impacts of density reduction across a range of progressively finer spatial scales: site, stand, hillslope position and neighbourhood. In particular, we focused on the influence of treatments beyond the boundaries of treated stands to include impacts on downslope and neighbouring stands across sites varying in soil moisture.Trees at the wet site responded with increased growth when compared with trees at the dry site. Additionally, trees in treated stands at the dry site responded with increased iWUE while trees at the wet site showed no difference in iWUE compared to untreated stands.We hypothesized that water is not the primary limiting factor for growth at our sites, but that density reduction released other resources, such as growing space or nutrients to drive the growth response. At progressively finer spatial scales we found that tree responses were not driven by hillslope location (i.e. downslope of treatment) but to changes in local neighbourhood tree density.Synthesis. This study demonstrated that water can be viewed as an agent to investigate cross-scale interactions as it links processes operating at coarse to finer spatial scales and vice versa. Consequently, management prescriptions such as density reductions to increase resistance and resilience of trees to climate change, specifically to drought, need to consider cross-scale interactions as specific magnitude and mechanisms of growth responses can only be predicted when multiple scales are taken into account.This study demonstrated that water can be viewed as an agent to investigate cross-scale interactions as it links processes operating at coarse to finer spatial scales and vice versa. Consequently, management prescriptions such as density reductions to increase resistance and resilience of trees to climate change, specifically to drought, need to consider cross-scale interactions, as specific magnitude and mechanisms of growth responses can only be predicted when multiple scales are taken into account.
      PubDate: 2017-03-27T05:11:58.415028-05:
      DOI: 10.1111/1365-2745.12749
       
  • Early life conditions and precipitation influence the performance of
           widespread understorey herbs in variable light environments
    • Authors: Andrea C. Westerband; Carol C. Horvitz
      Abstract: The understorey of tropical forests is heterogeneous across time, and plants that inhabit this layer may exhibit adaptations (e.g. trait plasticity) that enable them to exploit this variability to their advantage. We tested the hypothesis that two widespread understorey herbs would perform equally well in a variable as in a constant environment, using a 2-year shade-house experiment.We measured demographic traits (growth and survival), a physiological trait (maximum photosynthetic capacity), and life-history traits (leaf life span and biomass allocation) of Heliconia tortuosa and Calathea crotalifera. We investigated how these traits were affected by light availability at the seedling stage, precipitation, and whether individuals experienced a constant or variable light environment.Whether or not a variable environment was favourable for plants depended upon precipitation and the environment in which individuals started life. At low precipitation, plants in a variable light environment grew more than those in a constant environment, but only when individuals had lived as seedlings in low light. At high precipitation, plants in a constant environment grew more than those in a variable environment, regardless of early conditions. Survival was lower in a variable environment at low precipitation, and more so at high precipitation. Photosynthetic capacity was lower for individuals in a variable environment than in a constant environment when they had lived in high light as seedlings.Calathea grew faster and survived more poorly than Heliconia, independently of the treatments. Calathea grew more at high than low precipitation while Heliconia grew more at low than high precipitation. Leaf life span and biomass allocation did not differ among treatments, although Calathea had a significantly greater proportion of its biomass above-ground vs. that of Heliconia.Synthesis. Environmental variability had a neutral or positive effect on biomass allocation, photosynthetic capacity, and leaf life span for these species. Survival was the only trait that was always lower in a variable environment. The effect of environmental variability was dependent on early life conditions as well as precipitation, suggesting that generalist species may experience high fitness as forest environments become more variable by maintaining high growth at the expense of survival.Environmental variability had a neutral or positive effect on biomass allocation, photosynthetic capacity and leaf life span for two widespread, understorey herbs. Survival was always lower in a variable environment. The effect of environmental variability depended on earlier conditions and precipitation, suggesting that generalists may experience high fitness as environments become more variable by maintaining high growth but reduced survival.
      PubDate: 2017-03-27T05:11:50.529403-05:
      DOI: 10.1111/1365-2745.12757
       
  • Major shifts in species’ relative abundance in grassland mixtures
           alongside positive effects of species diversity in yield: a
           continental-scale experiment
    • Authors: Caroline Brophy; John A. Finn, Andreas Lüscher, Matthias Suter, Laura Kirwan, Maria-Teresa Sebastià, Áslaug Helgadóttir, Ole H. Baadshaug, Gilles Bélanger, Alistair Black, Rosemary P. Collins, Jure Čop, Sigridur Dalmannsdottir, Ignacio Delgado, Anjo Elgersma, Michael Fothergill, Bodil E. Frankow-Lindberg, An Ghesquiere, Barbara Golinska, Piotr Golinski, Philippe Grieu, Anne-Maj Gustavsson, Mats Höglind, Olivier Huguenin-Elie, Marit Jørgensen, Zydre Kadziuliene, Päivi Kurki, Rosa Llurba, Tor Lunnan, Claudio Porqueddu, Ulrich Thumm, John Connolly
      Abstract: Increased species diversity promotes ecosystem function; however, the dynamics of multi-species grassland systems over time and their role in sustaining higher yields generated by increased diversity are still poorly understood. We investigated the development of species’ relative abundances in grassland mixtures over 3 years to identify drivers of diversity change and their links to yield diversity effects.A continental-scale field experiment was conducted at 31 sites using 11 different four-species mixtures each sown at two seed abundances. The four species consisted of two grasses and two legumes, of which one was fast establishing and the other temporally persistent. We modelled the dynamics of the four-species mixtures, and tested associations with diversity effects on yield.We found that species’ dynamics were primarily driven by differences in the relative growth rates (RGRs) of competing species, and secondarily by density dependence and climate. The temporally persistent grass species typically had the highest RGRs and hence became dominant over time. Density dependence sometimes induced stabilising processes on the dominant species and inhibited shifts to monoculture. Legumes persisted at most sites at low or medium abundances and persistence was improved at sites with higher annual minimum temperature.Significant diversity effects were present at the majority of sites in all years and the strength of diversity effects was improved with higher legume abundance in the previous year. Observed diversity effects, when legumes had declined, may be due to (i) important effects of legumes even at low abundance, (ii) interaction between the two grass species or (iii) a store of N because of previous presence of legumes.Synthesis. Alongside major compositional changes driven by RGR differences, diversity effects were observed at most sites, albeit at reduced strength as legumes declined. This evidence strongly supports the sowing of multi-species mixtures that include legumes over the long-standing practice of sowing grass monocultures. Careful and strategic selection of the identity of the species used in mixtures is suggested to facilitate the maintenance of species diversity and especially persistence of legumes over time, and to preserve the strength of yield increases associated with diversity.Alongside major compositional changes driven by relative growth rate differences, diversity effects were observed at most sites, albeit at reduced strength as legumes declined. This evidence strongly supports the sowing of multi-species mixtures that include legumes over the long-standing practice of sowing grass monocultures. Careful and strategic selection of the identity of the species used in mixtures is suggested to facilitate the maintenance of species diversity and especially persistence of legumes over time, and to preserve the strength of yield increases associated with diversity.
      PubDate: 2017-03-27T05:11:45.712432-05:
      DOI: 10.1111/1365-2745.12754
       
  • Litter for life: assessing the multifunctional legacy of plant traits
    • Authors: André Tavares Corrêa Dias; Johannes H. C. Cornelissen, Matty P. Berg
      Abstract: Litter drives a wide variety of important functions in both terrestrial and aquatic ecosystems. However, the role of litter in regulating community dynamics and ecosystem processes has mostly been studied in terms of litter presence or amount. Besides in biogeochemistry, we still do not know how litters from distinct plant species differ in their effects on other ecosystem processes and services including biodiversity support.We briefly synthesize the multiple litter functions and services by using the afterlife legacy of interspecific variation in plant morphological, physical and chemical traits as a unifying tool. We do so by explicit reference to two highly distinct but possibly interacting ‘trait spectra’: the widely known Resource Economic Spectrum, and the Size and Shape Spectrum, a trait-based axis ranging from small and relatively simply shaped distal plant organs to large and more intricately shaped ones.Synthesis. Ecosystem services provided by plant litter are driven by either one of the trait spectra or by both. In this way, the Size and Shape Spectrum-Resource Economic Spectrum concept is a promising tool for understanding and predicting the contributions of different plant species, through the afterlife effects of their litter traits, to various important services in different ecosystems and human contexts.Ecosystem services provided by plant litter are driven by traits related to both the Size and Shape Spectrum (SSS) and the Resource Economic Spectrum (RES). In this way, the SSS-RES concept is a promising tool for understanding and predicting the contributions of different plant species, through the afterlife effects of their litter traits, to various important services in different ecosystems and human contexts.
      PubDate: 2017-03-27T05:11:20.328985-05:
      DOI: 10.1111/1365-2745.12763
       
  • Different response-effect trait relationships underlie contrasting
           responses to two chemical stressors
    • Authors: Christoph Mensens; Frederik De Laender, Colin R. Janssen, Koen Sabbe, Marleen De Troch
      Abstract: 1.Trait-based approaches evaluate ecosystem functioning under environmental change by relating traits predicting changes in species densities (response traits) to traits driving ecosystem functioning (effect traits). Stressors can however affect ecosystem functioning not only by altering species densities, but also by directly changing species effect traits.2.We first identified the response traits predicting the cell density of 18 marine benthic diatom strains along gradients of two chemical stressors (a pesticide and a metal, atrazine and copper). We then tested if response traits could predict stressor-induced changes in ecosystem functioning, i.e. changes in the effect traits driving the diatoms’ potential contribution to primary production, sediment stabilization and energy content in intertidal systems. Finally, we examined if changes in density and changes in ecosystem functioning were correlated, to assess whether species capable of growing under stressful conditions could maintain their contribution to ecosystem functioning.3.The relationship between response traits and stressor-induced changes in density and ecosystem functioning was different depending on stressor type: a set of intercorrelated morphological traits predicted changes in both density and ecosystem functioning under metal stress, with large cells being more stress-resistant. Changes in density and changes in ecosystem functioning were positively related: diatoms whose density was least affected by the metal were also able to sustain functioning under metal exposure.4.In contrast, the capacity for mixotrophic growth predicted changes in density, but not changes in ecosystem functioning under pesticide stress. Pesticide effects on density and on ecosystem functioning were negatively related for energy content and sediment stabilization, indicating a limited capacity of pesticide-tolerant diatoms to maintain their contribution to ecosystem functioning.5.Synthesis. Ecosystem functioning under stress can depend on whether the response traits driving changes in species densities also predict direct stress effects on the species’ contribution to functioning. Based on our results, we expect a disproportionate loss of functioning when traits driving species densities do not allow to maintain ecosystem functioning under stress.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-25T02:00:31.408079-05:
      DOI: 10.1111/1365-2745.12777
       
  • Genetic differentiation and plasticity interact along temperature and
           precipitation gradients to determine plant performance under climate
           change
    • Authors: Zuzana Münzbergová; Věroslava Hadincová, Hana Skálová, Vigdis Vandvik
      Abstract: Understanding species' abilities to cope with changing climate is a key prerequisite for predicting the future fates of species and ecosystems. Despite considerable research on species responses to changing climate, we still lack understanding of the role of specific climatic factors, and their interactions, for species responses. We also lack understanding of the relative importance of plasticity vs. adaptation in determining the observed responses.As a model, we use a dominant clonal grass, Festuca rubra, originating from a natural climatic grid of 12 localities in western Norway that allows factorial combinations of temperature (mean growing season temperatures ranging from 6·5 to 10·5 °C) and precipitation (annual precipitation ranging from 600 to 2700 mm). We grew clones from all populations in four growth chambers representing the four climatic extremes in the climate grid (warm/cold × wet/dry).Genetic differentiation and direction and magnitude of plastic responses vary systematically among populations throughout the climatic grid. Growth-related plant traits are highly plastic and their degree of plasticity depends on their origin. In contrast, the traits reflecting species' foraging strategy are not plastic but vary with the climate of origin. Levels of plasticity of growth-related traits and genetically differentiated foraging traits thus might constrain local populations' ability to cope with novel climates.Synthesis. Shifts in temperature and precipitation, at the scale and direction expected for the region in the next century, are likely to dramatically affect plant performance. This study illustrates how the interplay between genetic differentiation and plasticity in response to both temperature and precipitation will affect the specific responses of species to climate change. Such complex responses will affect how climate-change impacts scale up to the community and ecosystem levels. Future studies thus need to specifically consider regionally relevant climate-change projections, and also explore the role of genetic differentiation and plasticity and how this varies within local floras. Our study also demonstrates that even widespread species with seemingly broad climatic niches may strongly differ in their population performance and plasticity. Climate-change studies should therefore not be limited to rare and restricted species.Shifts in temperature and precipitation, at the scale and direction expected for the region in the next century, are likely to dramatically affect plant performance. This study illustrates how the interplay between genetic differentiation and plasticity in response to both temperature and precipitation will affect the specific responses of species to climate change. Such complex responses will affect how climate-change impacts scale up to the community and ecosystem levels. Future studies thus need to specifically consider regionally relevant climate-change projections, and also explore the role of genetic differentiation and plasticity and how this varies within local floras. Our study also demonstrates that even widespread species with seemingly broad climatic niches may strongly differ in their population performance and plasticity. Climate-change studies should therefore not be limited to rare and restricted species.
      PubDate: 2017-03-23T09:25:28.603346-05:
      DOI: 10.1111/1365-2745.12762
       
  • Greater root phosphatase activity in nitrogen-fixing rhizobial but not
           actinorhizal plants with declining phosphorus availability
    • Authors: Guochen K. Png; Benjamin L. Turner, Felipe E. Albornoz, Patrick E. Hayes, Hans Lambers, Etienne Laliberté
      Abstract: The abundance of nitrogen (N)-fixing plants in ecosystems where phosphorus (P) limits plant productivity poses a paradox because N fixation entails a high P cost. One explanation for this paradox is that the N-fixing strategy allows greater root phosphatase activity to enhance P acquisition from organic sources, but evidence to support this contention is limited.We measured root phosphomonoesterase (PME) activity of 10 N-fixing species, including rhizobial legumes and actinorhizal Allocasuarina species, and eight non-N-fixing species across a retrogressive soil chronosequence showing a clear shift from N to P limitation of plant growth and representing a strong natural gradient in P availability.Legumes showed greater root PME activity than non-legumes, with the difference between these two groups increasing markedly as soil P availability declined. By contrast, root PME activity of actinorhizal species was always lower than that of co-occurring legumes and not different from non-N-fixing plants.The difference in root PME activity between legumes and actinorhizal plants was not reflected in a greater or similar reliance on N fixation for N acquisition by actinorhizal species compared to co-occurring legumes.Synthesis. Our results support the idea that N-fixing legumes show high root phosphatase activity, especially at low soil P availability, but suggest that this is a phylogenetically conserved trait rather than one directly linked to their N-fixation capacity.Our results support the idea that N-fixing legumes show high root phosphatase activity, especially at low soil P availability, but suggest that this is a phylogenetically conserved trait rather than one directly linked to their N-fixation capacity.
      PubDate: 2017-03-23T08:05:58.52584-05:0
      DOI: 10.1111/1365-2745.12758
       
  • Soil biota suppress positive plant diversity effects on productivity at
           high but not low soil fertility
    • Authors: Shan Luo; Gerlinde B. De Deyn, Bin Jiang, Shixiao Yu
      Abstract: 1. Plant community productivity commonly increases with increasing plant diversity, which is explained by complementarity among plant species in resource utilization (complementarity effect), or by selection of particularly productive plant species in diverse plant communities (selection effect). Recent studies have also shown that soil biota can drive the positive plant diversity–productivity relationship by suppressing productivity more in low- than in high-diversity plant communities. However, much remains unknown about whether soil fertility plays a role in determining how soil biota affect plant diversity–productivity relationships.2.We hypothesized that under high soil fertility conditions, negative soil biota effects dominate, which reduces plant monoculture biomass more than that of high-diversity plant communities. Conversely, under low soil fertility conditions, we hypothesized positive soil biota effects dominate, which facilitates plant resource partitioning and enhances community-level biomass in high-diversity plant communities. Hence we expected positive plant diversity–community productivity relationships under low and high soil fertility conditions but caused by different mechanisms.3.We tested these hypotheses using woody seedlings and set up plant assemblages with four species richness levels (one, two, four and eight species), and grew them in sterilized and unsterilized (sterilized soil + living soil inoculum) soils at two nutrient levels (low vs. high fertility).4.We found that at high fertility negative soil biota effects dominated and suppressed plant community biomass more in high-diversity plant communities than in monocultures, resulting in reduced complementarity effects of diverse plant communities and a non-significant plant species richness–community biomass relationship in unsterilized soil. Whereas at low fertility soil biota had net neutral to positive effects on plant community biomass but the beneficial effects did not increase with increasing plant species richness. Instead, soil biota neutrally affected the positive plant species richness–community biomass relationship, presumably due to non-specific effects of beneficial soil biota.5.Synthesis. Soil biota and soil fertility interactively determine plant species richness–community biomass relationships. Moreover, soil biota modulate the complementary resource use among plant species. These findings suggest that environmental context plays an important role in determining whether and how soil biota generate the biodiversity–productivity relationship. Future studies would benefit from revealing the mechanisms underlying the interactive effects of soil biota, soil fertility, and plant diversity on ecosystem functioning.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-19T20:11:10.749153-05:
      DOI: 10.1111/1365-2745.12773
       
  • Phenological responsiveness to climate differs among four species of
           Quercus in North America
    • Authors: Katharine L. Gerst; Natalie L. Rossington, Susan J. Mazer
      Abstract: 1.The timing of the seasonal activity of organisms is a tractable indicator of climate change. Many studies in North America have investigated the role of temperature on the onset date of phenological transitions in temperate deciduous trees and found that the onset of leafing and flowering in numerous species has occurred earlier in recent years, apparently in response to higher temperatures in winter and spring.2.Few studies have examined the climatic and biogeographic drivers of phenological responses in water-limited ecosystems or explored inter-specific variation in responses of phenological metrics other than the timing of onset, such as the periodicity or duration of phenological activity.3.This study used phenological observations of four species of Quercus contributed to the USA National Phenology Network database from 2009-2014 to investigate how responses to climate (temperature and precipitation) and geographic location (latitude, longitude and elevation) varied among two western North American species (Q. agrifolia and Q. lobata) and two eastern and central North American species (Q. alba and Q. rubra).4.Within years, in species in the western, water-limited ecosystems, the phenological phases observed here (bud break, flowers or flower buds) tend to occur intermittently throughout the growing season, and each event is of longer duration than the same phenophases of the temperate-zone species, rendering a single onset date an incomplete metric with which to track responsiveness or to compare species. By contrast, the eastern/central U.S. species were phenologically more responsive than the western species to spatial and temporal variation in winter, spring, and fall precipitation and maximum temperature.5.Synthesis: Within and between regions these congeners exhibited a diversity of responses to seasonal temperature and precipitation. This indicates that for predictive model development it is critical to understand how each underlying driver influences species that are adapted to different climatic regimes. These results underscore the value of studying a range of phenological metrics and species from a variety of ecosystems to better predict phenological responses to short-term variation and to long-term change in climate.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-19T20:10:42.386321-05:
      DOI: 10.1111/1365-2745.12774
       
  • Invasive seaweeds transform habitat structure and increase biodiversity of
           associated species
    • Authors: Jennifer A. Dijkstra; Larry G. Harris, Kristen Mello, Amber Litterer, Christopher Wells, Colin Ware
      Abstract: The visual landscape of marine and terrestrial systems is changing as a result of anthropogenic factors. Often these shifts involve introduced species that are morphologically dissimilar to native species, creating a unique biogenic structure and habitat for associated species within the landscape. While community level changes as a result of introduced species have been documented in both terrestrial and marine systems, it is still unclear how long-term shifts in species composition will affect habitat complexity or its potential to influence the biodiversity of species that occur at the base of the food web.We analysed quadrat photos collected at several subtidal sites in the Gulf of Maine over a 30+ year period, and collected individual seaweed species to determine their complexity and the biodiversity of meso-invertebrates associated with each species.By coupling the relationship of 30+ years of shifts in seaweed assemblages, morphological structure of the seaweed assemblage, and their meso-invertebrates, we determined introduced seaweeds have increased by up to 90%, corresponding to a rise in two-dimensional (2D) structure, and a decline in canopy height of subtidal rocky habitats. The highly complex two-dimensional habitat provided by introduced filamentous red seaweeds supports 2 to 3 times more meso-invertebrate individuals and species that form the base of the food web than simpler forms of morphological habitat.Synthesis: The present study demonstrates a long-term shift in foundation species towards a dominance of invasive seaweeds that directly reduce canopy height and increase the 2D biogenic structure of the habitat. These introduced seaweeds harbour greater biodiversity of species found at the base of the food web than seaweeds with simpler forms such as the native kelp species. Such shifts in habitat structure will propagate to food-webs by influencing the structure of lower trophic level meso-invertebrates and indirectly upper trophic level species that feed on these invertebrates and use the seaweed structure as refuge.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-18T10:05:26.754573-05:
      DOI: 10.1111/1365-2745.12775
       
  • Expansion of deciduous tall shrubs but not evergreen dwarf shrubs
           inhibited by reindeer in Scandes mountain range
    • Authors: Tage Vowles; Bengt Gunnarsson, Ulf Molau, Thomas Hickler, Leif Klemedtsson, Robert G. Björk
      Abstract: One of the most palpable effects of warming in Arctic ecosystems is shrub expansion above the tree line. However, previous studies have found that reindeer can influence plant community responses to warming and inhibit shrubification of the tundra.We revisited grazed (ambient) and ungrazed study plots (exclosures), at the southern as well as the northern limits of the Swedish alpine region, to study long-term grazing effects and vegetation changes in response to increasing temperatures between 1995 and 2011, in two vegetation types (shrub heath and mountain birch forest).In the field layer at the shrub heath sites, evergreen dwarf shrubs had increased in cover from 26% to 49% but were unaffected by grazing. Deciduous dwarf and tall shrubs also showed significant, though smaller, increases over time. At the birch forest sites, the increase was similar for evergreen dwarf shrubs (20–48%) but deciduous tall shrubs did not show the same consistent increase over time as in the shrub heath.The cover and height of the shrub layer were significantly greater in exclosures at the shrub heath sites, but no significant treatment effects were found on species richness or diversity.July soil temperatures and growing season thawing degree days (TDD) were higher in exclosures at all but one site, and there was a significant negative correlation between mean shrub layer height and soil TDD at the shrub heath sites.Synthesis. This study shows that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. Tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures. However, the overriding vegetation shift across our sites was the striking increase in evergreen dwarf shrubs, which were not influenced by grazing. As the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.This study shows that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. Although tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures, the overriding vegetation shift across our sites was the striking increase in evergreen dwarf shrubs, which were not influenced by grazing. As the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.
      PubDate: 2017-03-16T05:51:12.242457-05:
      DOI: 10.1111/1365-2745.12753
       
  • Transmission and temporal dynamics of anther-smut disease (Microbotryum)
           on alpine carnation (Dianthus pavonius)
    • Authors: Emily L. Bruns; Janis Antonovics, Valentina Carasso, Michael Hood
      Abstract: Theory has shown that sterilizing diseases with frequency-dependent transmission (characteristics shared by many sexually transmitted diseases) can drive host populations to extinction.Anther-smut disease (caused by Microbotryum sp.) has become a model plant pathogen system for studying the dynamics of vector- and sexually transmitted diseases: infected individuals are sterilized, producing spores instead of pollen, and the disease is spread between reproductive individuals by insect pollinators. We investigated anther-smut disease in a heavily infected population of Dianthus pavonius (alpine carnation) over an 8-year period to determine disease impacts on host population dynamics.Over the 8 years, disease prevalence remained consistently high (>40%), while the host population numbers declined by over 50%.The observed rate of vector transmission to reproductive, adult hosts was inadequate to explain the high disease prevalence. Additional density-dependent aerial transmission to highly susceptible juveniles, indicated from experimental field and greenhouse studies, is likely to play a key role in maintaining the high disease prevalence.Epidemiological models that accounted for the mixed transmission mode predicted an eventual decline in disease.Synthesis. Our results demonstrate that high prevalence of a sterilizing disease does not necessarily drive host populations towards extinction and also highlights the importance of demographic studies for establishing the presence of alternative transmission modes.We studied the transmission dynamics of vector-borne sterilizing disease in a heavily diseased natural plant population for 8 years. Our results demonstrate that high disease prevalence does not necessarily drive host populations towards extinction and also highlights the importance of demographic studies for establishing the presence of alternative transmission modes.
      PubDate: 2017-03-13T06:45:56.731178-05:
      DOI: 10.1111/1365-2745.12751
       
  • Declines in low-elevation subalpine tree populations outpace growth in
           high-elevation populations with warming
    • Authors: Erin Conlisk; Cristina Castanha, Matthew J. Germino, Thomas T. Veblen, Jeremy M. Smith, Lara M. Kueppers
      Abstract: Species distribution shifts in response to climate change require that recruitment increase beyond current range boundaries. For trees with long life spans, the importance of climate-sensitive seedling establishment to the pace of range shifts has not been demonstrated quantitatively.Using spatially explicit, stochastic population models combined with data from long-term forest surveys, we explored whether the climate-sensitivity of recruitment observed in climate manipulation experiments was sufficient to alter populations and elevation ranges of two widely distributed, high-elevation North American conifers.Empirically observed, warming-driven declines in recruitment led to rapid modelled population declines at the low-elevation, ‘warm edge’ of subalpine forest and slow emergence of populations beyond the high-elevation, ‘cool edge’. Because population declines in the forest occurred much faster than population emergence in the alpine, we observed range contraction for both species. For Engelmann spruce, this contraction was permanent over the modelled time horizon, even in the presence of increased moisture. For limber pine, lower sensitivity to warming may facilitate persistence at low elevations – especially in the presence of increased moisture – and rapid establishment above tree line, and, ultimately, expansion into the alpine.Synthesis. Assuming 21st century warming and no additional moisture, population dynamics in high-elevation forests led to transient range contractions for limber pine and potentially permanent range contractions for Engelmann spruce. Thus, limitations to seedling recruitment with warming can constrain the pace of subalpine tree range shifts.Using stochastic demographic models combined with long-term forest survey data, we found that climate-driven changes to recruitment altered populations and elevation ranges of two widely distributed North American conifers. Rapid population declines at low elevations and slow emergence of populations beyond tree line led to transient range contractions for limber pine and potentially permanent range contractions for Engelmann spruce.
      PubDate: 2017-03-13T06:45:39.855523-05:
      DOI: 10.1111/1365-2745.12750
       
  • Plant traits, stoichiometry and microbes as drivers of decomposition in
           the rhizosphere in a temperate grassland
    • Authors: Yolima Carrillo; Colin Bell, Akihiro Koyama, Alberto Canarini, Claudia M. Boot, Matthew Wallenstein, Elise Pendall
      Abstract: 1.It is becoming increasingly clear that plant roots can impact the decomposition of existing soil C in the rhizosphere. Studies under controlled conditions suggest this impact may be plant-species dependent, but whether this is the case in natural conditions or what factors underlie this variation is mostly unknown.2.With a novel field-based isotopic approach combining 13C enriched glucose and BrdU additions, we compared in-situ C decomposition of added labile C and native soil C (priming) among eight semi-arid grassland species’ rhizospheres to investigate the factors driving inter-species variation. We examined the influence of several rhizosphere factors related to soil chemistry, microbial activity, microbial community, microbial stoichiometry, plant chemistry and root morphology.3.Plant species generated distinct microbial and chemical rhizosphere environments, which translated into differences in the direction, magnitude and temporal dynamics of the soil C priming. Soil C decomposition was positively related to soil C/P and soil N/P (via its influence on the bacterial community), which in turn were positively related to plant N/P. Plant C/N was also a significant factor via its negative influence on soil N/P. In contrast, the main direct predictors of labile C decomposition were microbial biomass, microbial C/N and the C degrading enzymes, which in turn were linked to root morphology and C chemistry.4.Synthesis. Within this community, plant species’ rhizospheres can vary in their susceptibility to C loss in response to changes in C availability. Soil stoichiometry, driven by plant chemical traits, appeared to be the strongest driver of priming. Our study suggests that shifts in plant communities involving increases in N relative to P have the greatest potential to lead to C loss. We provide evidence of root morphology and C chemistry as drivers of labile C processing in soil, a novel empirical contribution to our understanding of the role of plant traits belowground. The contrasting regulation of different pools of soil C suggest observations of the regulation of simple C compounds should not be extrapolated to the whole C pool. Our findings provide support for rhizosphere-driven mechanisms by which shifts in plant community composition could have implications on the ecosystem-level C balance.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-10T09:12:07.627318-05:
      DOI: 10.1111/1365-2745.12772
       
  • Climate, soil and plant functional types as drivers of global fine-root
           trait variation
    • Authors: Grégoire T. Freschet; Oscar J. Valverde-Barrantes, Caroline M. Tucker, Joseph M. Craine, Luke M. McCormack, Cyrille Violle, Florian Fort, Christopher B. Blackwood, Katherine R. Urban-Mead, Colleen M. Iversen, Anne Bonis, Louise H. Comas, Johannes H. C. Cornelissen, Ming Dong, Dali Guo, Sarah E. Hobbie, Robert J. Holdaway, Steven W. Kembel, Naoki Makita, Vladimir G. Onipchenko, Catherine Picon-Cochard, Peter B. Reich, Enrique G. de la Riva, Stuart W. Smith, Nadejda A. Soudzilovskaia, Mark G. Tjoelker, David A. Wardle, Catherine Roumet
      Abstract: 1.Ecosystem functioning relies heavily on belowground processes, which are largely regulated by plant fine-roots and their functional traits. However, our knowledge of fine-root trait distribution relies to date on local- and regional-scale studies with limited numbers of species, growth forms and environmental variation.2.We compiled a worldwide fine-root trait dataset, featuring 1115 species from contrasting climatic areas, phylogeny and growth forms to test a series of hypotheses pertaining to the influence of plant functional types, soil and climate variables, and the degree of manipulation of plant growing conditions on species fine-root trait variation. Most particularly, we tested the competing hypotheses that fine-root traits typical of faster return on investment would be most strongly associated with conditions of limiting versus favourable soil resource availability. We accounted for both data source and species phylogenetic relatedness.3.We demonstrate that (1) Climate conditions promoting soil fertility relate negatively to fine-root traits favouring fast soil resource acquisition, with a particularly strong positive effect of temperature on fine-root diameter and negative effect on specific root length (SRL), and a negative effect of rainfall on root nitrogen concentration; (2) Soil bulk density strongly influences species fine-root morphology, by favouring thicker, denser fine-roots; (3) Fine-roots from herbaceous species are on average finer and have higher SRL than those of woody species, and N2-fixing capacity positively relates to root nitrogen; (4) Plants growing in pots have higher SRL than those grown in the field.4.Synthesis. This study reveals both the large variation in fine-root traits encountered globally and the relevance of several key plant functional types and soil and climate variables for explaining a substantial part of this variation. Climate, particularly temperature, and plant functional types were the two strongest predictors of fine-root trait variation. High trait variation occurred at local scales, suggesting that wide-ranging belowground resource economics strategies are viable within most climatic areas and soil conditions.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-08T02:56:01.275675-05:
      DOI: 10.1111/1365-2745.12769
       
  • Deer-mediated changes in environment compound the direct impacts of
           herbivory on understorey plant communities
    • Authors: Autumn E. Sabo; Katie L. Frerker, Donald M. Waller, Eric L. Kruger
      Abstract: In forests of eastern North America, white-tailed deer (Odocoileus virginianus) can directly affect, via herbivory, the presence, abundance and reproductive success of many plant species. In addition, deer indirectly influence understorey communities by altering environmental conditions.To examine how deer indirectly influence understorey plants via environmental modification, we sampled vegetation and environmental variables in- and outside deer exclosures (10–20 years old) located in temperate forests in northern Wisconsin and the Upper Peninsula of Michigan, USA. We assessed how excluding deer affected understorey community composition and structure, the soil and light environment, and relationships between direct and indirect effects, using non-metric multidimensional scaling (NMDS), mixed linear models and nonparametric multiplicative regression (NPMR).Excluding deer altered sapling communities and several aspects of the understorey environment. Excluding deer from plots with lower overstory basal area increased sapling abundance, decreasing the amount of light available to groundlayer plants. Exclusion also reduced soil compaction and the thickness of the soil E horizon.The composition of understorey communities covaried in apparent response to the environmental factors affected by exclusion. In several common species and groups, E horizon thickness, compaction, openness, and/or total (sapling and overstory) basal area were significant predictors of plant frequency.Complementary analyses revealed that deer exclusion also altered the frequency distributions of several species and groups across environmental space.Synthesis. Deer alter many facets of the understorey environment, such as light availability, soil compaction and thickness of the soil E horizon, which, in turn, appear to mediate variation in plant communities. Those environmental modifications likely compound direct impacts of herbivory as drivers of understorey community change. Our results provide evidence that deer effects on the environment have important implications for forest composition. Thus, we suggest a re-examination of the common assumption that understorey community shifts stem primarily from tissue removal.Deer alter many facets of the understorey environment, such as light availability, soil compaction and thickness of the soil E horizon, which, in turn, appear to mediate variation in plant communities (e.g. data shown above for a, graminoids and b, Liliaceae). Those environmental modifications likely compound direct impacts of herbivory as drivers of understorey community change. Our results provide evidence that deer effects on the environment have important implications for forest composition.
      PubDate: 2017-03-02T19:05:28.887437-05:
      DOI: 10.1111/1365-2745.12748
       
  • The seasonal climate niche predicts phenology and distribution of an
           ephemeral annual plant, Mollugo verticillata
    • Authors: Joe Hereford; Johanna Schmitt, David D. Ackerly
      Abstract: Many short-lived species complete their life cycles during brief seasonal windows of favourable environmental conditions. Such species may persist in the face of climate warming by migration to track their seasonal climate niche in space and/or by phenological shifts to track favourable conditions in time within the year. To describe the seasonal climate niche of the short-lived annual Mollugo verticillata in California, we used data from herbarium specimens and historic climate records to estimate environmental conditions at the location, month and year of each collection.We used these data in a MaxEnt framework to construct a seasonal species distribution model (SDM) of the species’ climate niche within the total climate space available across all seasons and locations in California. The model provides fine-scale spatial and temporal predictions of habitat suitability, predicting both where and when the species should be observed.We compared the predictions of the model to those from a conventional SDM based on mean annual climate data. Both models showed that M. verticillata is limited to warm environments within California. However, the seasonal SDM also predicted phenology by mapping climate suitability across the state for each month of the year. Mollugo verticillata is limited to warm months, and its seasonal climate niche shifts in space across California in the course of the year.We used the seasonal SDM to map the predicted future species distribution for each month of the year under three warming scenarios. The species is predicted to expand its range and occur earlier in the year in most locations; in the warmest locations, seasonal suitability is predicted to decline in the warmest months, which may result in bimodal phenology with a mid-summer gap.Synthesis. We developed a novel species distribution model using herbarium records and monthly weather data, which predicts not only where a short-lived species should be found but also when during the year it is predicted to occur in those areas. This model can be used to predict how climate change will affect the species distribution in space as well as seasonal phenology across the landscape.We developed a novel species distribution model using herbarium records and monthly weather data, which predicts not only where a short-lived species should be found but also when during the year it is predicted to occur in those areas. This model can be used to predict how climate change will affect the species distribution in space as well as seasonal phenology across the landscape.
      PubDate: 2017-03-02T05:05:45.860956-05:
      DOI: 10.1111/1365-2745.12739
       
  • Biological Flora of the British Isles: Milium effusum
    • Authors: Pieter De Frenne; Jörg Brunet, Mathias Cougnon, Guillaume Decocq, Bente J. Graae, Jenny Hagenblad, Martin Hermy, Annette Kolb, Isgard H. Lemke, Shiyu Ma, Anna Orczewska, Jan Plue, Guy Vranckx, Monika Wulf, Kris Verheyen
      Abstract: This account presents information on all aspects of the biology of Milium effusum L. (Wood Millet) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, and conservation.The grass Milium effusum is a common species of mature woodland in central and southern England, but is less common in the wetter parts of northern England, Wales, Scotland and Ireland. World-wide, the species is native to many temperate, boreal, subarctic and subalpine parts of the northern hemisphere: from eastern North America across most of Europe (excluding Mediterranean climates) to the Ural Mountains and Black Sea, extending eastwards to the Himalaya, Korea and Japan.Wood Millet is a shade-tolerant, relatively tall grass (up to 1·8 m) producing up to 700 caryopses per individual. It is characteristic of temperate deciduous woodland, but can also occur in other woodland and forest types and even in scrub, alpine meadows, along railways and roads, and on rocks. In woods, it is one of the most conspicuous plants of the herb layer in the early summer after the disappearance of spring flowering species. While the species is generally considered an ancient woodland indicator in England and western Europe, it is also known to colonize secondary, post-agricultural forests relatively rapidly in other areas such as Denmark, southern Sweden and Poland.The species has a wide amplitude in terms of soil acidity and nutrient availability, but predominantly grows on soils of intermediate soil fertility and soil pH and with high organic matter concentration. However, M. effusum can tolerate large quantities of tree-leaf litter on the forest floor and is able to grow on very acidic soils.Changes in land use, climate, densities of large herbivores and atmospheric deposition of nitrogen are having effects on populations of Wood Millet. Significant responses of the life-history traits and population characteristics have been detected in response to environmental variation and to experimental treatments of temperature, nutrients, light and acidity. In many of its habitats across its range, M. effusum is currently becoming more frequent. During the last century, its mean elevation of occurrence in upland areas of Europe has also increased by several hundreds of metres. Typically, management actions are directed towards the conservation of its main habitat type (e.g. ancient woodlands of the Milio-Fagetum association) rather than to the species specifically.The shade-tolerant grass Milium effusum is a common feature of mature woodlands in England, but is less common in the wetter parts of the British Isles. It has a wide distribution in the northern hemisphere from eastern North America to Japan. Miliumeffusum is currently becoming more frequent in many of its habitats across its range, probably because of a combination of changes in land use, climate, increased densities of large herbivores and atmospheric N deposition.
      PubDate: 2017-03-01T06:36:44.150149-05:
      DOI: 10.1111/1365-2745.12744
       
  • Climate variability and community stability in Mediterranean shrublands:
           the role of functional diversity and soil environment
    • Authors: Ignacio M. Pérez-Ramos; Ricardo Díaz-Delgado, Enrique G. Riva, Rafael Villar, Francisco Lloret, Teodoro Marañón
      Abstract: Understanding how different factors mediate the resistance of communities to climatic variability is a question of considerable ecological interest that remains mostly unresolved. This is particularly remarkable to improve predictions about the impact of climate change on vegetation.Here, we used a trait-based approach to analyse the sensitivity to climatic variability over 9 years of 19 Mediterranean shrubland communities located in southwest Spain. We evaluated the role of functional diversity (FD) and soil environment as drivers of community stability (assessed as changes in plant cover, species diversity and composition).The studied shrubland communities were strongly sensitive to inter-annual variability in climate. First, colder and drier conditions caused remarkable decreases in total plant cover but increased FD, likely because the reduction of plant cover after harsh climatic conditions promoted the expansion of functionally dissimilar species in the new open microsites; although communities returned to their initial values of plant cover after nine years, changes in FD and structure persisted over time. Second, drier and colder conditions favoured the predominance of shrubs with a conservative resource-use strategy (i.e. with higher dry matter content in leaves, stems and roots), bigger seeds and a more efficient use of water.The most functionally diverse communities were the most stable over time in terms of species diversity, likely because a higher number of functionally dissimilar species allowed compensatory dynamics among them.Communities inhabiting more acidic and resource-limited environments were less variable over time, probably because they were mainly constituted by slow-growth, stress-tolerant species that are potentially better adapted to harsh climatic conditions.Synthesis. This study highlights the utility of a trait-based approach to evaluate how plant communities respond to climatic variability. We could infer that the increased frequency of extreme climatic events predicted by climatic models will alter the functional structure of shrubland communities, with potential repercussions for ecosystem functioning. Our results also provide new insights into the role of FD and soil environment as buffers of the climate impact on woody communities, as well as potentially useful information to be applied in ecologically based management and restoration strategies.We used a trait-based approach to analyse the sensitivity to climatic variability of 19 Mediterranean shrublands located in southwest Spain. We also evaluated the role of functional diversity and soil environment as drivers of community stability. We could infer that the increased frequency of extreme climatic events predicted by climatic models will alter the functional structure of these communities, with potential repercussions for ecosystem functioning.
      PubDate: 2017-02-28T09:00:28.045078-05:
      DOI: 10.1111/1365-2745.12747
       
  • Local demographic and epidemiological patterns in the Linum
           marginale–Melampsora lini association: a multi-year study
    • Authors: Hanna Susi; Peter H. Thrall, Luke G. Barrett, Jeremy J. Burdon
      Abstract: Many theoretical and empirical studies operate from an assumption that pathogens have a significant influence on the fecundity and life span of their host species. However, there are surprisingly little data investigating the long-term fitness impacts and genetic consequences that arise from pathogen infection in natural populations. Here, we address this gap through the analysis of a dataset investigating the local population dynamics of a native host plant (Linum marginale) and an associated rust pathogen (Melampsora lini) across 12 years.To investigate patterns of disease prevalence and severity and track effects on host fecundity and demography, we conducted censuses on an annual basis at a single site. Annual M. lini infection prevalence ranged from 0% to 99%. Severe epidemics occurred in 3- to 4-year cycles causing high overwintering mortality and subsequent changes in the relative abundance of different host phenotypes. Host population size oscillated in response to epidemics and declined towards the end of the observation period. Changes in host numbers were found to affect disease severity but not infection prevalence.Melampsora lini infection increased L. marginale fecundity; the infected plants produced threefold more seed capsules on average than uninfected plants (13·3 vs. 4·3 seed capsules per plant).To investigate how variation in environmental conditions affects epidemiology and host demography, we identified climatic factors affecting host growth, overwintering and disease severity. Winter (June) rainfall increased host overwintering success and summer (December) rainfall favoured host growth. The progress of M. lini disease epidemics benefited from optimal temperatures in February and suffered from rainfall in January.We further examined links between the genetic structure of the pathogen population and disease dynamics. There was a positive correlation between mean pathogen infectivity (as measured across a host differential set) and the severity of disease epidemics.Synthesis. Our results provide new insights into local drivers and consequences of pathogen epidemiology in natural populations. Melampsora lini infection can have profound consequences on the phenotype, demography and population structure of Linum marginale by increasing host fecundity, overwinter mortality and disease resistance.Our results provide new insights into local drivers and consequences of pathogen epidemiology in natural populations. Melampsora lini infection can have profound consequences on the phenotype, demography and population structure of Linum marginale by increasing host fecundity, overwinter mortality and disease resistance.
      PubDate: 2017-02-27T10:11:58.532049-05:
      DOI: 10.1111/1365-2745.12740
       
  • Plant functional connectivity – integrating landscape structure and
           effective dispersal
    • Authors: Alistair G. Auffret; Yessica Rico, James M. Bullock, Danny A. P. Hooftman, Robin J. Pakeman, Merel B. Soons, Alberto Suárez-Esteban, Anna Traveset, Helene H. Wagner, Sara A. O. Cousins
      Abstract: Dispersal is essential for species to survive the threats of habitat destruction and climate change. Combining descriptions of dispersal ability with those of landscape structure, the concept of functional connectivity has been popular for understanding and predicting species’ spatial responses to environmental change.Following recent advances, the functional connectivity concept is now able to move beyond landscape structure to consider more explicitly how other external factors such as climate and resources affect species movement. We argue that these factors, in addition to a consideration of the complete dispersal process, are critical for an accurate understanding of functional connectivity for plant species in response to environmental change.We use recent advances in dispersal, landscape and molecular ecology to describe how a range of external factors can influence effective dispersal in plant species, and how the resulting functional connectivity can be assessed.Synthesis. We define plant functional connectivity as the effective dispersal of propagules or pollen among habitat patches in a landscape. Plant functional connectivity is determined by a combination of landscape structure, interactions between plant, environment and dispersal vectors, and the successful establishment of individuals. We hope that this consolidation of recent research will help focus future connectivity research and conservation.We define plant functional connectivity as the effective dispersal of propagules or pollen among habitat patches in a landscape. Plant functional connectivity is determined by a combination of landscape structure, interactions between plant, environment and dispersal vectors, and the successful establishment of individuals. We hope that our consolidation of recent research will help focus future connectivity research and conservation.
      PubDate: 2017-02-27T10:11:52.382619-05:
      DOI: 10.1111/1365-2745.12742
       
  • Nitrogen deposition and climate change have increased vascular plant
           species richness and altered the composition of grazed subalpine
           grasslands
    • Authors: Marion Boutin; Emmanuel Corcket, Didier Alard, Luis Villar, Juan-José Jiménez, Cian Blaix, Cédric Lemaire, Gilles Corriol, Thierry Lamaze, André Pornon
      Abstract: Atmospheric nitrogen (N) deposition and climate warming are two major components of global change that drive species richness and composition in plant communities. However, their combined effects have been insufficiently investigated across large spatial and temporal scales particularly in high-elevation, nutrient-limited ecosystems.We examine whether and how N deposition and climate warming have altered the plant richness and the composition of subalpine semi-natural, extensively grazed grasslands of the Pyrenees, using two complementary approaches: (i) analysis of 553 relevés to explore vegetation changes across large ecological gradients including temperature and N deposition (spatial approach) and (ii) a re-sampling of a subset of 40 sites among the 553 sites to assess temporal changes over the past decades (temporal approach).Both approaches showed that the vascular plant species richness increased when temperature and cumulative N deposition increase, shifting the species composition towards more thermophilic and eutrophic communities.Synthesis. We hypothesize that the release from abiotic constraints (milder temperature and higher nitrogen availability) due to global changes and long-standing extensive grazing counteracting the negative effects of nitrogen deposition have been responsible for the diversity and compositional changes of plant communities over the last decades in the Pyrenees. Thus, in contrast with other grasslands, high-elevation grazed grasslands may increase in species diversity with nitrogen deposition under climate warming.We hypothesize that the release from abiotic constraints (milder temperature and higher nitrogen availability) due to global changes and long-standing extensive grazing counteracting the negative effects of nitrogen deposition have been responsible for the diversity and compositional changes of plant communities over the last decades in the Pyrenees. Thus, in contrast with other grasslands, high-elevation grazed grasslands may increase in species diversity with nitrogen deposition under climate warming.
      PubDate: 2017-02-27T10:11:44.086573-05:
      DOI: 10.1111/1365-2745.12743
       
  • Evolutionary responses to land use in eight common grassland plants
    • Authors: Eva Völler; Oliver Bossdorf, Daniel Prati, Harald Auge
      Abstract: Land-use change is an important component of global environmental change and a major driver of current declines in biodiversity. Although there is increasing evidence that species can evolve rapidly in response to anthropogenic environmental change, comprehensive studies of the evolutionary consequences of land use are still fairly scarce, in particular such that consider multiple species, study many populations, or that discriminate between different aspects of land use.Here, we studied genetic change of key phenotypic traits in response to land use in eight common grassland species across 137 grassland sites covering a broad range of land-use types (mowing and/or grazing, with or without fertilization) and intensities in three regions of Germany.A common garden study revealed significant genetic differentiation in response to land-use intensification within all of the investigated species. Among the studied land-use processes, mowing appeared to have the strongest effect on the differentiation of plant phenotypes, with flowering phenology as the most responsive trait. However, there was substantial variation among species in the magnitude, sometimes also the direction of the observed population differentiation.Synthesis. Our study demonstrates that evolutionary responses of grassland plants to land-use change are a common phenomenon and widespread across a broad range of different species. These evolutionary changes are likely to impact biotic interactions, as well as the structure and functioning of communities and ecosystems.Our study demonstrates that evolutionary responses of grassland plants to land-use change are a common phenomenon and widespread across a broad range of different species. These evolutionary changes are likely to impact biotic interactions, as well as the structure and functioning of communities and ecosystems.
      PubDate: 2017-02-27T10:11:38.331495-05:
      DOI: 10.1111/1365-2745.12746
       
  • Rapid transgenerational effects in Knautia arvensis in response to plant
           community diversity
    • Authors: Tanja Rottstock; Volker Kummer, Markus Fischer, Jasmin Joshi
      Abstract: Plant species persistence in natural communities requires coping with biotic and abiotic challenges. These challenges also depend on plant community composition and diversity. Over time, biodiversity effects have been shown to be strengthened via increasing species complementarity in mixtures. Little is known, however, whether differences in community diversity and composition induce rapid transgenerational phenotypic adaptive differentiation during community assembly. We expect altered plant–plant and other biotic interactions (mutualists or antagonists) in high vs. low diverse communities to affect immediate within- and between-species trait differentiations due to competition for light and nutrients.Three years after the initiation of a large-scale, long-term biodiversity experiment in Jena, Germany, we tested for effects of varying experimental plant community diversity (1–60 plant species; one to four plant functional groups) and composition (with or without legumes and/or grasses) on phenotypic differentiation and variation of the tall herb Knautia arvensis. We measured reproduction at different diversity levels in the Jena Experiment (residents hereafter) and, in an additional common garden experiment without competition, recorded subsequent offspring performance (i.e. growth, reproductive success and susceptibility to powdery mildew) to test for differentiation in phenotypic expression and variability.We observed phenotypic differences among diversity levels with reduced fecundity of K. arvensis residents in more diverse communities. In the next generation grown under common garden conditions, offspring from high-diversity plots showed reduced growth (i.e. height) and lower reproduction (i.e. fewer infructescences), but increased phenotypic trait variability (e.g. in leaf width and powdery mildew presence) and also tended to be less susceptible to powdery mildew infection.Community composition also affected Knautia parents and offspring. In the presence of legumes, resident plants produced more seeds (increased fecundity); however, germination rate of those seeds was reduced at an early seedling stage (reduced fertility).Synthesis. We conclude that rapid transgenerational effects of community diversity and composition on both mean and variation of phenotypic traits among offspring exist. In addition to heritable variation, environmentally induced epigenetic and/or maternal processes matter for early plant community assembly and may also determine future species coexistence and community stability.Plants occur in communities of few to many species. We observed diversity and composition of maternal communities to affect early, transgenerational phenotypic differentiation and variation of Knautia arvensis offspring under common garden conditions. We propose that environmentally induced epigenetic or maternal processes, in addition to heritable variation, matter for plant community assembly and may affect species coexistence and community stability. Photo: Powdery mildew infection (Erysiphe knautiae, Duby) on K. arvensis residents in the Jena-Experiment. Photo credit: Tanja Rottstock.
      PubDate: 2017-02-27T10:00:48.031205-05:
      DOI: 10.1111/1365-2745.12689
       
  • Do impacts of an invasive nitrogen-fixing shrub on Douglas-fir and its
           ectomycorrhizal mutualism change over time following invasion?
    • Authors: Sara Grove; Ingrid M. Parker, Karen A. Haubensak
      Abstract: 1.Impacts of invasive species may change in magnitude and even direction with invasion age. Impacts could increase as the population increases, individuals grow in size, and ecological changes accumulate.2.We used a chronosequence approach to characterize the development of soil impacts over time following the invasion of Cytisus scoparius, a widespread nitrogen-fixing shrub thought to limit reforestation success. In a greenhouse experiment, we evaluated how abundance of ectomycorrhizal fungi, Douglas-fir performance, and leaf nitrogen changed across a 3-31 year chronosequence of invasion. Each of the chronosequence sites were clearcuts where reforestation efforts were unsuccessful and where C. scoparius invaded. To estimate the contributions of the invasion separately from contributions of the accompanying disturbance, i.e. deforestation, we included soils from both invaded and uninvaded patches in each site of the chronosequence. In a complementary soil conditioning experiment, we examined the separate effects of host absence and invader presence on the mycorrhizal mutualism, leaf nitrogen, and seedling growth.3.Ectomycorrhizal colonization was lower in invaded soil, but this effect did not intensify with time. Despite the suppression of the mutualism, Douglas-fir grew larger in invaded soils. This positive response is likely due to nitrogen fertilization, a conclusion supported by higher concentrations of leaf nitrogen of Douglas-fir grown in invaded soils. While leaf N concentration increased with invasion duration, Douglas-fir survival and growth did not.Synthesis. Our findings suggest that soil impacts of an invader can develop rapidly and can be surprisingly stable over time. In such systems, recently invaded areas may be as difficult to restore as long invaded areas, especially where ectomycorrhizal fungi are important drivers of reforestation success. More chronosequence studies or long time series are needed to evaluate whether this is a general pattern.This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-24T14:10:24.306734-05:
      DOI: 10.1111/1365-2745.12764
       
  • Seed dispersal distributions resulting from landscape-dependent daily
           movement behaviour of a key vector species, Anas platyrhynchos
    • Authors: Erik Kleyheeg; Jelle Treep, Monique Jager, Bart A. Nolet, Merel B. Soons
      Abstract: Dispersal via animals (zoochory) is a primary mechanism for seed exchange between habitat patches. Recent studies have established that many plant species can survive waterbird gut passage. To quantify the patterns and consequences of waterbird-mediated dispersal, information on ingestion and gut passage must be combined with bird movement data. Such analysis has recently revealed seed dispersal kernels by migrating waterbirds. However, since many waterbird populations are largely resident, and migrating populations spend only a minor part of the main dispersal season (autumn–winter) on active migration, daily regional-scale movements probably cause more frequent dispersal.We synthesized high-resolution empirical data on landscape-scale movements and seed gut passage times in a key disperser species, the mallard (Anas platyrhynchos), using a spatially explicit, mechanistic model to quantify dispersal distributions resulting from daily autumn–winter movements. We evaluated how landscape composition and seed traits affect these dispersal patterns.The model indicates that mallards generate highly clumped seed deposition patterns, dispersing seeds primarily between core areas used for foraging and resting. Approximately 34% of all dispersed seeds are transported to communal roost areas, which may function as reservoirs for mallard-dispersed species, and 7% are transported between foraging areas. Landscape-dependent movement patterns strongly affect the dispersal distributions, resulting in multi-modal dispersal kernels, with dispersal distances increasing with fragmentation of freshwater foraging habitat. Seed size-related gut retention times determine the proportion of seeds being dispersed away from the ingestion area, with larger seeds (20 mm3) having a 8–10% higher potential for long-distance dispersal than smaller seeds (0·2 mm3), if surviving gut passage. However, twice as many small seeds will finally accomplish long-distance dispersal due to their higher gut passage survival.Synthesis. Firstly, this study reveals how seed dispersal patterns resulting from daily waterfowl movements are shaped by landscape-dependent differences in movement patterns. Secondly, seed survival appears more important than retention time in determining the scale of long-distance dispersal by non-migrating mallards. We conclude that the frequent flights of staging waterbirds result in directed dispersal over distances inversely related to wetland availability, indicating that they maintain landscape connectivity across a range from wet to increasingly dry landscapes.Our mechanistic model of endozoochorous dispersal by a keystone waterbird species, the mallard Anas platyrhynchos, reveals that seed deposition patterns are shaped by landscape-dependent movement patterns of the vector, rather than seed trait-related gut passage times. Dispersal distances are inversely related to wetland availability, indicating that staging waterbirds help maintain landscape connectivity in increasingly fragmented landscapes.
      PubDate: 2017-02-21T19:01:02.868533-05:
      DOI: 10.1111/1365-2745.12738
       
  • Thermal segregation drives patterns of alder and willow expansion in a
           montane ecosystem subject to climate warming
    • Authors: Christina L. Rinas; Roman J. Dial, Patrick F. Sullivan, T. Scott Smeltz, S. Carl Tobin, Michael Loso, Jason E. Geck
      Abstract: Tall-shrub expansion into low-statured communities, a hallmark of recent vegetative change across tundra ecosystems, involves three major genera: Alnus, Betula and Salix. Which genus expands most into tundra landscapes will determine ecosystem properties.We show that Alnus and Salix shrubs segregate thermal space (elevation × insolation) and colonize tundra landscapes differently in response to climate warming, thereby replacing different tundra types.Vegetative change estimated from repeat photography should account for hill-slope. Methodologically, slope determines surface area estimated from orthophotos as projected pixel area times secant of pixel slope. Ecologically, the change in thermally responsive vegetative area is sensitive to terrain steepness, scaling as the cosecant of hill-slope, so that studies should expect more shrub expansion in areas of shallow slopes than steep slopes.Repeat aerial photography in Alaska's Chugach Mountains from 1972 to 2012 orthorectified on a high-resolution lidar digital elevation model indicated tall Salix was rare in 1972 and colonized warmer slopes by 2012. Tall Alnus colonized steeper, cooler slopes both by 2012 and by 1972. Salix and forest colonized similar thermal space. Colonization probability for both shrub genera was maximized at intermediate elevations.Alnus colonization adjacent to dwarf-shrub tundra was twenty times as likely as Salix colonization. Salix colonization adjacent to low-shrub/herbaceous tundra was three times as likely as Alnus colonization. Replacement of dwarf-shrub tundra by Alnus and of low-shrub/herbaceous communities by Salix will affect herbivores and soil properties.Good agreement between observations of plant functional type and multinomial predictions in a thermal space defined by elevation and insolation suggested that these two variables were sufficient for forecast modelling. Spatially explicit, climate-driven generalized linear multinomial and random forest classification models in available thermal space forecast surface areas of forest, Alnus, Salix and tundra over a range of warming, modelled as upward shifted isotherms, including expected IPCC scenarios. Both modelling approaches indicated that shrubs may respond nonlinearly to warming.Synthesis. The provision of taxon-specific coefficients for climate-driven, spatially explicit models using high-resolution digital elevation models is necessary for accurately forecasting vegetative change due to climate warming in montane and arctic regions.The provision of taxon-specific coefficients for climate-driven, spatially explicit models using high-resolution digital elevation models is necessary for accurately forecasting vegetative change due to climate warming in montane and arctic regions.
      PubDate: 2017-02-20T05:25:43.492099-05:
      DOI: 10.1111/1365-2745.12737
       
  • A six thousand-year record of climate and land-use change from
           Mediterranean seagrass mats
    • Authors: Lourdes López-Merino; Nieves R. Colás-Ruiz, María F. Adame, Oscar Serrano, Antonio Martínez Cortizas, Miguel A. Mateo
      Abstract: The Mediterranean seagrass Posidonia oceanica maintains a biodiverse ecosystem and it is a world-wide important carbon sink. It grows for millennia, accumulating organic-rich soils (mats) beneath the meadows. This marine habitat is protected by the European Union; however, it is declining rapidly due to coastal development. Understanding its response to disturbances could inform habitat restoration, but many environmental impacts predate monitoring programs (
      PubDate: 2017-02-20T05:25:32.651127-05:
      DOI: 10.1111/1365-2745.12741
       
  • The tortoise and the hare: reducing resource availability shifts
           competitive balance between plant species
    • Authors: Dean E. Pearson; Yvette K. Ortega, John L. Maron
      Abstract: Determining how changes in abiotic conditions influence community interactions is a fundamental challenge in ecology. Meeting this challenge is increasingly imperative in the Anthropocene where climate change and exotic species introductions alter abiotic context and biotic composition to reshuffle natural systems.We created plant assemblages consisting of monocultures or equal abundance of the native community dominant bluebunch wheatgrass (Pseudoroegneria spicata) and the exotic spotted knapweed (Centaurea stoebe), a co-occurring invasive forb that has overtaken grasslands across the western United States. We subjected these composition treatments to drought (20% of average precipitation vs. average) and herbivory on C. stoebe by its biocontrol agent Cyphocleonus achates to explore how reduced precipitation might influence the effects of competition and biocontrol herbivory on C. stoebe's abundance.At the end of 7 years, C. stoebe dominated mixed-species plots under normal precipitation conditions, with biomass 50% greater than that of the native P. spicata. However, under drought stress, P. spicata's biomass was>200% greater than C. stoebe's. Interestingly, both species were impervious to drought in monoculture, indicating the importance of the drought by competition interaction. The biocontrol herbivore reduced C. stoebe abundance and indirectly increased P. spicata biomass in mixed-species drought plots, but these effects were only marginally significant and relatively weak. Overall, C. stoebe abundance was primarily driven by the drought by competition interaction, with negatively additive but weak effects of the drought by herbivory interaction.The response of the exotic to the treatments was driven by rapid changes in population density linked to its fast life-history strategy, while the native's response was driven by changes in per capita plant biomass linked to its slower life-history strategy. Individual plant performance metrics did not predict overall population responses for the invader, indicating the importance of longer term population measures.Synthesis. These results demonstrate that reduced precipitation inputs linked to climate change can dramatically shift the balance of plant competition, even toggling the advantage from exotic to native dominance. They also illustrate the importance of biotic interactions in predicting species responses to abiotic change.The superinvader spotted knapweed loses to native dominant under drought. This study demonstrates that reduced precipitation inputs linked to climate change can dramatically shift the balance of plant competition, toggling the advantage from exotic to native dominance. Results also illustrate the importance of biotic interactions for predicting species responses to abiotic change, a finding with significant ramifications for assisted migration.
      PubDate: 2017-02-09T06:40:31.632682-05:
      DOI: 10.1111/1365-2745.12736
       
  • Testing the environmental filtering concept in global drylands
    • Authors: Yoann Le Bagousse-Pinguet; Nicolas Gross, Fernando T. Maestre, Vincent Maire, Francesco Bello, Carlos Roberto Fonseca, Jens Kattge, Enrique Valencia, Jan Leps, Pierre Liancourt
      Abstract: The environmental filtering hypothesis predicts that the abiotic environment selects species with similar trait values within communities. Testing this hypothesis along multiple – and interacting – gradients of climate and soil variables constitutes a great opportunity to better understand and predict the responses of plant communities to ongoing environmental changes.Based on two key plant traits, maximum plant height and specific leaf area (SLA), we assessed the filtering effects of climate (mean annual temperature and precipitation, precipitation seasonality), soil characteristics (soil pH, sand content and total phosphorus) and all potential interactions on the functional structure and diversity of 124 dryland communities spread over the globe. The functional structure and diversity of dryland communities were quantified using the mean, variance, skewness and kurtosis of plant trait distributions.The models accurately explained the observed variations in functional trait diversity across the 124 communities studied. All models included interactions among factors, i.e. climate–climate (9% of explanatory power), climate–soil (24% of explanatory power) and soil–soil interactions (5% of explanatory power). Precipitation seasonality was the main driver of maximum plant height, and interacted with mean annual temperature and precipitation. Soil pH mediated the filtering effects of climate and sand content on SLA. Our results also revealed that communities characterized by a low variance can also exhibit low kurtosis values, indicating that functionally contrasting species can co-occur even in communities with narrow ranges of trait values.Synthesis. We identified the particular set of conditions under which the environmental filtering hypothesis operates in drylands world-wide. Our findings also indicate that species with functionally contrasting strategies can still co-occur locally, even under prevailing environmental filtering. Interactions between sources of environmental stress should be therefore included in global trait-based studies, as this will help to further anticipate where the effects of environmental filtering will impact plant trait diversity under climate change.We identified the particular set of conditions under which the environmental filtering hypothesis operates in drylands world-wide. Our findings also indicate that species with functionally contrasting strategies can still co-occur locally, even under prevailing environmental filtering. Interactions between sources of environmental stress should be therefore included in global trait-based studies, as this will help to further anticipate where the effects of environmental filtering will impact plant trait diversity under climate change.
      PubDate: 2017-02-06T05:21:02.88362-05:0
      DOI: 10.1111/1365-2745.12735
       
  • Measuring and predicting the influence of traits on the assembly processes
           of wood-inhabiting fungi
    • Authors: Nerea Abrego; Anna Norberg, Otso Ovaskainen
      Abstract: The identification of traits that influence the responses of the species to environmental variation provides a mechanistic perspective on the assembly processes of ecological communities. While much research linking functional ecology with assembly processes has been conducted with animals and plants, the development of predictive or even conceptual frameworks for fungal functional community ecology remains poorly explored. Particularly, little is known about the contribution of traits to the occurrences of fungal species under different environmental conditions.Wood-inhabiting fungi are known to strongly respond to habitat disturbance, and thus provide an interesting case study for investigating to what extent variation in occurrence patterns of fungi can be related to traits. We apply a trait-based joint species distribution model to a data set consisting of fruit-body occurrence data on 321 wood-inhabiting fungal species collected in 22 460 dead wood units from managed and natural forest sites.Our results show that environmental filtering plays a big role on shaping wood-inhabiting fungal communities, as different environments held different communities in terms of species and trait compositions. Most importantly, forest management selected against species with large and long-lived fruit-bodies as well as late decayers, and promoted the occurrences of species with small fruit-bodies and early decayers. A strong phylogenetic signal in the data suggested the existence of also some other functionally important traits than the ones we considered.We found that those species groups that were more prevalent in natural conditions had more associations to other species than species groups that were tolerant to or benefitted from forest management. Therefore, the changes that forest management causes on wood-inhabiting fungal communities influence ecosystem functioning through simplification of interactive associations among the fungal species.Synthesis. Our results show that functional traits are linked to the responses of wood-inhabiting fungi to variation in their environment, and thus environmental changes alter ecosystem functions via promoting or reducing species with different fruit-body types. However, further research is needed to identify other functional traits and to provide conclusive evidence for the adaptive nature of the links from traits to occurrence patterns found here.Our results show that functional traits are linked to the responses of wood-inhabiting fungi to variation in their environment, and thus environmental changes alter ecosystem functions via promoting or reducing species with different fruit-body types. However, further research is needed to identify further functional traits and to provide conclusive evidence for the adaptive nature of the links from traits to occurrence patterns found here.
      PubDate: 2017-02-06T05:20:53.252615-05:
      DOI: 10.1111/1365-2745.12722
       
  • Towards a trait-based ecology of wetland vegetation
    • Authors: Helen Moor; Håkan Rydin, Kristoffer Hylander, Mats B. Nilsson, Regina Lindborg, Jon Norberg
      Abstract: Functional traits mechanistically capture plant responses to environmental gradients as well as plant effects on ecosystem functioning. Yet most trait-based theory stems from terrestrial systems and extension to other habitats can provide new insights.Wetlands differ from terrestrial systems in conditions (e.g. soil water saturation, anoxia, pH extremes), plant adaptations (e.g. aerenchyma, clonality, ubiquity of bryophytes) and important processes (e.g. denitrification, peat accumulation, methane emission). Wetland plant adaptations and trait (co-)variation can be situated along major plant trait trade-off axes (e.g. the resource economics spectrum), but soil saturation represents a complex stress gradient beyond a simple extension of commonly studied water availability gradients.Traits that affect ecosystem functioning overlap with patterns in terrestrial systems. But wetland-specific traits that mediate plant effects on soil redox conditions, microbial communities and on water flow, as well as trait spectra of mosses, vary among wetland types.Synthesis. With increasing availability of quantitative plant traits a trait-based ecology of wetlands is emerging, with the potential to advance process-based understanding and prediction. We provide an interactive cause-and-effect framework that may guide research efforts to disentangle the multiple interacting processes involved in scaling from environmental conditions to ecosystem functioning via plant communities.With the increasing availability of quantitative plant traits a trait-based ecology of wetlands is emerging, with the potential to advance process-based understanding and prediction. We provide an interactive cause-and-effect framework that may guide research efforts to disentangle the multiple interacting processes involved in scaling from environmental conditions to ecosystem functioning via plant communities.
      PubDate: 2017-02-02T05:30:56.016069-05:
      DOI: 10.1111/1365-2745.12734
       
  • Responses of common and rare aliens and natives to nutrient availability
           and fluctuations
    • Authors: Yanjie Liu; Mark Kleunen
      Abstract: Global environmental change not only includes changes in mean environmental conditions but also in temporal environmental fluctuations. Because it is frequently suggested that common species, and particularly invasive alien species, are phenotypically highly plastic, they might benefit more from these fluctuations than rare native and rare alien species. Experimental tests, however, are still lacking.Here, we tested whether alien plant species take more advantage of increases in resource levels and fluctuations therein than native species, and whether common species do so more than rare species. Therefore, we grew seven common alien, seven rare alien, nine common native and six rare native herbaceous plants, in one treatment with constantly low nutrient availability and five treatments with high nutrient availability that differed in temporal availability of nutrients (constant, increasing, decreasing, single large pulse, multiple smaller pulses).We found that all species produced more biomass and longer roots, and had a lower root mass fraction under high nutrient conditions than under low nutrient conditions, irrespective of their origin and commonness. Among the high nutrient treatments, the temporal pattern of nutrient supply also influenced biomass production, root allocation and root thickness, but the magnitude and/or directions of these responses varied among the groups of species. Particularly, we found that alien plant species, irrespective of whether they are common or rare, produced more biomass, and had a higher root mass fraction when nutrients were supplied as a single pulse in the middle of the growth period instead of supplied at a constant rate, whereas the reverse was true for the native species.Synthesis. Our study suggests that species origin does not drive differences in plant biomass production, root morphology and allocation in response to changes in mean environmental nutrient availability. However in our study, alien plant species, in contrast to native plant species, benefited from a large nutrient pulse. This suggests that increased fluctuations in nutrient availability might promote alien plant invasions.Although the fluctuating-resource-availability hypothesis has been a key hypothesis in invasion biology, few experimental studies have explicitly tested it by using fluctuating nutrient levels. Our multi-species experiment corroborate it, and in addition provide evidence that both common and rare naturalized alien plant species could benefit from a large nutrient pulse.
      PubDate: 2017-02-02T05:30:49.040386-05:
      DOI: 10.1111/1365-2745.12733
       
  • Masting synchrony in northern hardwood forests: super-producers govern
           population fruit production
    • Authors: David M. Minor; Richard K. Kobe
      Abstract: Trees commonly reproduce via masting cycles, which involves synchronized inter-annual variability in fruit crop size. A few individuals in a population will commonly produce much more fruit than others. If these trees produce fruit more frequently, as indicated by a lower inter-annual variability in fruit production, they may dominate fruit production over time.By measuring fruit production of 1635 individuals of 10 temperate tree species across 4 years in northern lower Michigan, we estimated the inter-annual variability and synchrony in each species. We compared fruit production estimates with measurements of tree size, soil nutrient availability and neighbourhood crowding to investigate the source of inter-individual variation in number of fruit produced.We found that trees’ fruit production increased with tree size. The trees that accounted for the largest proportion of total fruit production had lower inter-annual variability and higher synchrony in fruit production. These ‘super-producer’ trees tended to have high nutrient availability and few neighbouring trees, but there were no effects of nutrient availability or neighbourhood crowding on fruit production in the population as a whole.Synthesis. Masting is a population-level phenomenon, and is typically studied at this level. However, when we apply individual tree observations of fruit production to this phenomenon, it reveals super-producers which produce fruit more consistently than the rest of the population. By reducing inter-annual variability in fruit production, but increasing synchrony and making large numbers of fruit, super-producers may be able to reap the benefits of masting while governing population fruit production over time.Masting is a population-level phenomenon, and is typically studied at this level. However, when we apply individual tree observations of fruit production to this phenomenon, it reveals super-producers which produce fruit more consistently than the rest of the population. By reducing inter-annual variability in fruit production, but increasing synchrony and making large numbers of fruit, super-producers may be able to reap the benefits of masting while governing population fruit production over time.
      PubDate: 2017-02-02T05:30:42.866692-05:
      DOI: 10.1111/1365-2745.12729
       
  • Stoichiometric N:P flexibility and mycorrhizal symbiosis favour plant
           resistance against drought
    • Authors: Pierre Mariotte; Alberto Canarini, Feike A. Dijkstra
      Abstract: Drought induces changes in the nitrogen (N) and phosphorus (P) cycle but most plant species have limited flexibility to take up nutrients under such variable or unbalanced N and P availability. Both the degree of flexibility in plant N:P ratio and of root symbiosis with arbuscular mycorrhizal fungi might control plant resistance to drought-induced changes in nutrient availability, but this has not been directly tested.Here, we examined the role of plant N:P stoichiometric status and mycorrhizal symbiosis in the drought-resistance of dominant and subordinate species in a semi-natural grassland.We reduced water availability using rainout shelters (control vs. drought) and measured how plant biomass responded for the dominant and subordinate species. We then selected a dominant (Paspalum dilatatum) and a subordinate species (Cynodon dactylon), for which we investigated the N:P stoichiometric status, mycorrhizal root colonization and water-use efficiency.The biomass of all dominant plant species, but not subordinate species, decreased under drought. Drought increased soil available nitrogen, and thus increased soil N:P ratio, due to decreasing plant N uptake. The dominant P. dilatatum showed a high degree of plant N:P homeostasis and a considerable reduction in biomass under drought. At the opposite, the more flexible subordinate species C. dactylon increased its N uptake and water-use efficiency, apparently due to stronger symbiosis with mycorrhizae, and maintained its biomass.Synthesis. We conclude that the maintenance of N:P homeostasis in dominant species, possibly because of a large root nutrient foraging capacity, becomes inefficient when water stress limits N mobility in the soil. By contrast, we demonstrate that higher stoichiometric N:P flexibility coupled with stronger mutualistic association with mycorrhizae allow subordinate species to better withstand drought perturbations. Using a stoichiometric approach in a field experiment, our study provides for the first time clear and novel understandings of the mechanisms involved in drought-resistance within the plant-mycorrhizae-soil system.Using a stoichiometric approach in a field experiment, our study provides for the first time clear and novel understandings of the mechanisms involved in drought-resistance within the plant-mycorrhizae-soil system. Specifically, we demonstrate that higher stoichiometric N:P flexibility coupled with stronger mutualistic association with mycorrhizae allow subordinate species to better withstand drought perturbations compared to homeostatic and low mycorrhized dominant species.
      PubDate: 2017-02-02T05:30:30.783485-05:
      DOI: 10.1111/1365-2745.12731
       
  • Invasive plants accelerate nitrogen cycling: evidence from experimental
           woody monocultures
    • Authors: Insu Jo; Jason D. Fridley, Douglas A. Frank
      Abstract: Although it is widely believed that non-native invasive species threaten the functional integrity of forest ecosystems, their impact on important ecosystem processes such as nitrogen (N) cycling is not well understood.To examine how invasive species alter ecosystem N dynamics, we established monocultures of five phylogenetic pairs of native and non-native invasive understory woody species common to Eastern U.S. forests.After 3 years, we found invaders increased N cycling by enhancing the flow of N to the soil through greater litter N production and litter N content, and increased the uptake of available soil N, via greater fine root production and specific root length.Synthesis. Our results highlight the importance of linking above- and below-ground processes to better understand invader impacts on ecosystem nutrient processes. The rapid shifts in soil N processes as a result of invader dominance observed in our study suggest that invaders may be an important driver of forest ecosystem functioning.Experimental evidence of how invaders alter ecosystem processes such as soil nitrogen (N) cycling is rare, particularly for woody invaders. Here, we present a 3-year monoculture study that examined above- and below-ground plant traits and soil properties to test how forest woody invaders alter soil N cycling. Our results suggest that invaders promote soil N cycling through greater litter input and faster soil N uptake than co-occurring native species, which may significantly impact the dynamics of a key limiting nutrient in forest ecosystems.
      PubDate: 2017-02-02T05:30:26.182601-05:
      DOI: 10.1111/1365-2745.12732
       
  • Species interactions increase the temporal stability of community
           
    • Authors: Miren Río; Hans Pretzsch, Ricardo Ruíz-Peinado, Evy Ampoorter, Peter Annighöfer, Ignacio Barbeito, Kamil Bielak, Gediminas Brazaitis, Lluís Coll, Lars Drössler, Marek Fabrika, David I. Forrester, Michael Heym, Václav Hurt, Viktor Kurylyak, Magnus Löf, Fabio Lombardi, Ekaterina Madrickiene, Bratislav Matović, Frits Mohren, Renzo Motta, Jan Ouden, Maciej Pach, Quentin Ponette, Gerhard Schütze, Jerzy Skrzyszewski, Vit Sramek, Hubert Sterba, Dejan Stojanović, Miroslav Svoboda, Tzvetan M. Zlatanov, Andrés Bravo-Oviedo
      Abstract: There is increasing evidence that species diversity enhances the temporal stability (TS) of community productivity in different ecosystems, although its effect at the population and tree levels seems to be negative or neutral. Asynchrony in species responses to environmental conditions was found to be one of the main drivers of this stabilizing process. However, the effect of species mixing on the stability of productivity, and the relative importance of the associated mechanisms, remain poorly understood in forest communities.We investigated the way mixing species influenced the TS of productivity in Pinus sylvestris L. and Fagus sylvatica L. forests, and attempted to determine the main drivers among overyielding, asynchrony between species annual growth responses to environmental conditions, and temporal shifts in species interactions. We used a network of 93 experimental plots distributed across Europe to compare the TS of basal area growth over a 15-year period (1999–2013) in mixed and monospecific forest stands at different organizational levels, namely the community, population and individual tree levels.Mixed stands showed a higher TS of basal area growth than monospecific stands at the community level, but not at the population or individual tree levels. The TS at the community level was related to asynchrony between species growth in mixtures, but not to overyielding nor to asynchrony between species growth in monospecific stands. Temporal shifts in species interactions were also related to asynchrony and to the mixing effect on the TS.Synthesis. Our findings confirm that species mixing can stabilize productivity at the community level, whereas there is a neutral or negative effect on stability at the population and individual tree levels. The contrasting findings regarding the relationships between the temporal stability and asynchrony in species growth in mixed and monospecific stands suggest that the main driver in the stabilizing process may be the temporal niche complementarity between species rather than differences in species’ intrinsic responses to environmental conditions.Our findings confirm that species mixing can stabilize productivity at the community level but not at the population and tree levels. The different relationships between the mixing effect on the temporal stability and species asynchrony in mixed and monospecific stands suggests that temporal niche complementarity between species may be the main driver rather than differences in species’ intrinsic responses to environmental conditions.
      PubDate: 2017-02-01T04:52:33.379922-05:
      DOI: 10.1111/1365-2745.12727
       
  • Contrasting mass-ratio vs. niche complementarity effects on litter C and N
           loss during decomposition along a regional climatic gradient
    • Authors: Pablo García-Palacios; E. Ashley Shaw, Diana H. Wall, Stephan Hättenschwiler
      Abstract: The mass-ratio and niche complementarity mechanisms drive the influence of litter trait diversity on decomposition. However, the implications of these mechanisms remain poorly understood, as few studies have evaluated their importance relative to environmental conditions and soil decomposers when assessing different processes during decomposition (e.g. C dynamics and N transformations).We measured litter C and N losses during decomposition in 10 litter mixtures and calculated community-weighted means (CWM) and dissimilarity (Rao's Q) of 13 litter traits as metrics of the mass-ratio and niche complementarity mechanisms respectively. The 10 litter mixtures were incubated along a regional gradient (10 sites) in southern France over a year, where local environmental conditions (climate and soil parameters), and soil decomposers (microbes, nematodes, and macrofauna) were considered as drivers of decomposition.Sites and litter mixtures represented a wide range of environmental conditions, decomposers, and litter diversity. Litter mixture was the major factor affecting litter C and N loss. N was immobilized during the early decomposition stages (up to c. 40% mass loss), especially in mixtures of low N concentrations. Litter CWM traits were the key drivers of litter C and N loss, but litter trait dissimilarity emerged as a major driver of litter N loss. Macrofauna played a significant role on C and N loss, but environmental conditions exerted a minor influence.Our results highlight that distinct aspects of trait diversity in mixed species litter can play a more important role than environmental conditions and decomposers, which can affect the cycling of litter C and N at regional scales. Rather than opposing mass-ratio and niche complementarity mechanisms, our study shows that both can play a critical role simultaneously in litter decomposition.Synthesis. Our study emphasizes that, in the current context of global biodiversity decline, the mass-ratio and niche complementarity mechanisms should be considered to assess litter decomposition dynamics under global change. As litter diversity mechanisms distinctly affected the cycling of C and N, we recommend taking into account such element-specific effects to improve the prediction of the impacts of biodiversity change on biogeochemical cycles.Our study emphasizes that, in the current context of global biodiversity decline, the mass-ratio and niche complementarity mechanisms should be considered to assess litter decomposition dynamics under global change. As litter diversity mechanisms distinctly affected the cycling of C and N, we recommend taking into account such element-specific effects to improve the prediction of the impacts of biodiversity change on biogeochemical cycles.
      PubDate: 2017-01-31T04:56:23.601365-05:
      DOI: 10.1111/1365-2745.12730
       
  • ACC deaminase-producing rhizosphere bacteria modulate plant responses to
           flooding
    • Authors: Mohammadhossein Ravanbakhsh; Rashmi Sasidharan, Laurentius A. C. J. Voesenek, George A. Kowalchuk, Alexandre Jousset
      Abstract: Flooding events are predicted to increase over the coming decades, calling for a better understanding of plant responses to submergence. Specific root-associated microbes alter plant hormonal balance, affecting plant growth and stress tolerance. We hypothesized that the presence of such microbes may modulate plant responses to submergence.We tested whether root-associated bacteria producing the enzyme ACC (1-aminocyclopropane-1-carboxylate) deaminase affect submergence responses in Rumex palustris, a flood-tolerant riparian plant. Ethylene is a key plant hormone regulating flood-associated acclimations, and ACC deaminase activity of bacteria may decrease ethylene levels in the plant. Rumex palustris plants were inoculated with Pseudomonas putida UW4 or an isogenic mutant lacking ACC deaminase, and subsequently exposed to complete submergence.Submergence triggered ethylene-mediated responses, including an increase in leaf elongation and shoot fresh weight. Flood responses, including post-submergence ethylene production, were reduced in plants inoculated with ACC deaminase-producing wild type bacteria, as compared to plants inoculated with the ACC deaminase-negative mutant.Synthesis. We demonstrate that root-associated bacteria can alter plant response to environmental stress by altering plant hormonal balance. Plant–microbe interactions may thus be an overseen driver of plant life-history strategies that should be taken into account when assessing plant ecological adaptations such as abiotic stress resistance.We demonstrate that root-associated bacteria can alter plant response to environmental stress by altering plant hormonal balance. Plant–microbe interactions may thus be an overseen driver of plant life-history strategies that should be taken into account when assessing plant ecological adaptations such as abiotic stress resistance.
      PubDate: 2017-01-30T10:20:37.218178-05:
      DOI: 10.1111/1365-2745.12721
       
  • Above- and below-ground responses of four tundra plant functional types to
           deep soil heating and surface soil fertilization
    • Authors: Peng Wang; Juul Limpens, Liesje Mommer, Jasper Ruijven, Ake L. Nauta, Frank Berendse, Gabriela Schaepman-Strub, Daan Blok, Trofim C. Maximov, Monique M.P.D. Heijmans
      Abstract: Climate warming is faster in the Arctic than the global average. Nutrient availability in the tundra soil is expected to increase by climate warming through (i) accelerated nutrient mobilization in the surface soil layers, and (ii) increased thawing depths during the growing season which increases accessibility of nutrients in the deeper soil layers. Both processes may initiate shifts in tundra vegetation composition. It is important to understand the effects of these two processes on tundra plant functional types.We manipulated soil thawing depth and nutrient availability at a Northeast-Siberian tundra site to investigate their effects on above- and below-ground responses of four plant functional types (grasses, sedges, deciduous shrubs and evergreen shrubs). Seasonal thawing was accelerated with heating cables at c. 15 cm depth without warming the surface soil, whereas nutrient availability was increased in the surface soil by adding slow-release NPK fertilizer at c. 5 cm depth. A combination of these two treatments was also included. This is the first field experiment specifically investigating the effects of accelerated thawing in tundra ecosystems.Deep soil heating increased the above-ground biomass of sedges, the deepest rooted plant functional type in our study, but did not affect biomass of the other plant functional types. In contrast, fertilization increased above-ground biomass of the two dwarf shrub functional types, both of which had very shallow root systems. Grasses showed the strongest response to fertilization, both above- and below-ground. Grasses were deep-rooted, and they showed the highest plasticity in terms of vertical root distribution, as grass root distribution shifted to deep and surface soil in response to deep soil heating and surface soil fertilization respectively.Synthesis. Our results indicate that increased thawing depth can only benefit deep-rooted sedges, while the shallow-rooted dwarf shrubs, as well as flexible-rooted grasses, take advantage of increased nutrient availability in the upper soil layers. Our results suggest that grasses have the highest root plasticity, which enables them to be more competitive in rapidly changing environments. We conclude that root vertical distribution strategies are important for vegetation responses to climate-induced increases in soil nutrient availability in Arctic tundra, and that future shifts in vegetation composition will depend on the balance between changes in thawing depth and nutrient availability in the surface soil.Our results indicate that increased thawing depth can only benefit deep-rooted sedges, while the shallow-rooted dwarf shrubs as well as flexible-rooted grasses take advantage of increased nutrient availability in the upper soil layers. Our results suggest that grasses have the highest root plasticity, which enables them to be more competitive in rapidly changing environments. We conclude that root vertical distribution strategies are important for vegetation responses to climate-induced increases in soil nutrient availability in Arctic tundra, and that future shifts in vegetation composition will depend on the balance between changes in thawing depth and nutrient availability in the surface soil.
      PubDate: 2017-01-30T06:11:17.367339-05:
      DOI: 10.1111/1365-2745.12718
       
  • Intraspecific variability in growth response to environmental fluctuations
           modulates the stabilizing effect of species diversity on forest growth
    • Authors: Raphaël Aussenac; Yves Bergeron, Claudele Ghotsa Mekontchou, Dominique Gravel, Kamil Pilch, Igor Drobyshev
      Abstract: Differences between species in their response to environmental fluctuations cause asynchronized growth series, suggesting that species diversity may help communities buffer the effects of environmental fluctuations. However, within-species variability of responses may impact the stabilizing effect of growth asynchrony.We used tree ring data to investigate the diversity–stability relationship and its underlying mechanisms within the temperate and boreal mixed woods of Eastern Canada. We worked at the individual tree level to take into account the intraspecific variability of responses to environmental fluctuations.We found that species diversity stabilized growth in forest ecosystems. The asynchrony of species’ response to climatic fluctuations and to insect outbreaks explained this effect. We also found that the intraspecific variability of responses to environmental fluctuations was high, making the stabilizing effect of diversity highly variable.Synthesis. Our results are consistent with previous studies suggesting that the asynchrony of species’ response to environmental fluctuations drives the stabilizing effect of diversity. The intraspecific variability of these responses modulates the stabilizing effect of species diversity. Interactions between individuals, variation in tree size and spatial heterogeneity of environmental conditions could play a critical role in the stabilizing effect of diversity.Species diversity may help tree communities buffer the effects of environmental fluctuations. This stabilizing effect stems from the asynchrony of species growth due to species differences in their response to environmental fluctuations. However, within-species variability of responses may modulate the stabilizing effect of diversity. Mechanisms at the origin of this variability, therefore, play a crucial role in the diversity–stability relationship.
      PubDate: 2017-01-30T06:11:13.306378-05:
      DOI: 10.1111/1365-2745.12728
       
  • Predicting the global incidence of seed desiccation sensitivity
    • Authors: Sarah V. Wyse; John B. Dickie
      Abstract: The ability of seeds to tolerate desiccation plays an important role in plant regeneration ecology. Globally, the majority of species produce desiccation-tolerant (orthodox) seeds, while comparatively few produce desiccation-sensitive (recalcitrant) seeds that are unable to survive dehydration. The trait has important implications for species conservation, as desiccation-sensitive species cannot be conserved using traditional seed banking techniques. In addition, these species may be less resilient to the increases in droughts predicted for some regions under climate change scenarios.The best available resource on seed desiccation tolerance is the Royal Botanic Gardens, Kew's Seed Information Database. This database contains seed desiccation-sensitivity data for over 18 000 taxa, approximately 3% of which have desiccation-sensitive seeds. However, this database is likely biased towards desiccation-tolerant species. Previous attempts to estimate the proportion of seed plants with desiccation-sensitive seeds have ranged from 7% to 50%. Here, we aimed to overcome sampling bias to derive a best estimate for the proportion of seed plants with desiccation-sensitive seeds, based on current data.We used a recently developed method, based on taxonomic relatedness, to account for sampling bias and estimate the proportion of seed plants with desiccation-sensitive seeds. As a comparison, given that seed desiccation sensitivity is strongly related to habitat, we repeated our analyses using habitat as a basis.The predictions from our taxonomy-based models ranged between estimates of 7·5% and 19·6% of the world's seed-plant species with desiccation-sensitive seeds, depending on model type, while the habitat-based models suggested a value of approximately 8%. Our evidence suggests that, based on current data, the best estimate of the proportion of species with desiccation-sensitive seeds is likely to be approximately 8%. Tropical and subtropical moist broadleaf forests had the highest incidence of seed desiccation sensitivity, where an estimated 18·5% of the seed-plant flora possessed the trait.Synthesis. Alongside our estimation of the numbers of species with desiccation-sensitive seeds, we provide data on taxa and habitats where this trait may be most prevalent. These findings can be used to support conservation planning, particularly with respect to providing decision support for in and ex situ conservation techniques.We aimed to overcome sampling bias to derive a best estimate for the proportion of seed plants with desiccation-sensitive seeds, based on current data. Model results suggest that this figure is likely to be approximately 8% of seed plants globally. Alongside our estimates of the global incidence of this seed trait, we provide data on taxa and habitats where the trait may be most prevalent. Our findings can be used to support conservation planning, particularly with respect to providing decision support for in and ex situ conservation techniques.
      PubDate: 2017-01-30T06:11:09.017435-05:
      DOI: 10.1111/1365-2745.12725
       
  • Moving forward: insights and applications of moving-habitat models for
           climate change ecology
    • Authors: Melanie A. Harsch; Austin Phillips, Ying Zhou, Margaret-Rose Leung, D. Scott Rinnan, Mark Kot
      Abstract: Predicting and managing species’ responses to climate change is one of the most significant challenges of our time. Tools are needed to address problems associated with novel climatic conditions, biotic interactions and greater climate velocities.We present a spatially explicit moving-habitat model (MHM) and demonstrate its versatility in tackling critical questions in climate change research, including dispersal in multiple spatial dimensions, population stage structure, interspecific interactions, asymmetric range shifts, Allee effects and the presence of infectious diseases. The model utilizes integrodifference equations to track changes in population density over time in a habitat that is moving. The model is quite flexible and can accommodate variation in demography, dispersal patterns, biotic interaction and stochasticity in the velocity of climate change.The methods provide a general mechanistic understanding of the underlying ecological processes that drive a system. Field data can be readily incorporated into the model to give insight into specific populations of interest and inform management decisions.Synthesis. Moving-habitat models unite ecological theory, data-centred modelling and conservation decision support under a single framework. Their ability to generate testable hypotheses, incorporate data and inform best management practices proves that these models provide a valuable framework for climate change biologists.Moving habitat models utilize integrodifference equations to track changes in population density over time in a habitat that is moving. They unite ecological theory, data-centered modelling and conservation decision support under a single framework. Their ability to generate testable hypotheses, incorporate data and inform best management practices proves that these models provide a valuable framework for climate change biologists. URLs for interactive web applications to explore the models and code for one model are provided.
      PubDate: 2017-01-30T06:11:04.518411-05:
      DOI: 10.1111/1365-2745.12724
       
  • General allometric scaling of net primary production agrees with plant
           adaptive strategy theory and has tipping points
    • Authors: David G. Jenkins; Simon Pierce
      Abstract: Allometric scaling of net primary production (NPP) with plant biomass (B) is important to ecological carbon dynamics and energetics. Metabolic theory predicts a nonlinear power law for NPP scaling, based on fractal vascular systems, resulting in a linear model when using log NPP/log B axes that are standard in allometry. Alternatively, two other hypotheses predict nonlinear models for log-transformed data, with potential tipping points. Size-based competition may cause a quadratic curve as larger plants limit NPP by smaller plants. More inclusively, the plant adaptive strategies hypothesis predicts a sigmoidal curve to represent those same competitive effects, plus stress and ruderal adaptations that maintain relatively low NPP in habitats that are abiotically limiting or disturbed.We evaluated all three hypotheses for terrestrial vascular plants, using information theoretic model selection based on the Akaike Information Criterion (AICc). Published data (N = 709) were organised in subsets according to reported organisational level and plant growth form. Alternative curves were compared for a general model (using all data) and per subset. Potential tipping points were estimated using segmented regression.The plant adaptive strategies hypothesis was supported in general (AICc weight = 1·00) and via internal consistency for five of six subsets (86% of data). Competition was supported as affecting NPP at greater B, where quadratic and sigmoidal models often coincided. Only non-woody assemblages most plausibly fit a power law model, perhaps related to sparse data at lowest B.Synthesis. Adaptive strategies and corresponding environmental conditions appear to constrain terrestrial net primary production scaling relative to metabolic theory's ideal. Moreover, tipping points in general nonlinear net primary production scaling (at c. 38 and 360 g m−2 B) indicate thresholds for rapid changes in net primary production given changing B that occurs via changing climate, human appropriation and land use.Adaptive strategies and corresponding environmental conditions appear to constrain terrestrial NPP scaling relative to metabolic theory's ideal. Moreover, tipping points in general nonlinear NPP scaling (at c. 38 and 360 g m−2 B) indicate thresholds for rapid changes in NPP given changing B that occurs via changing climate, human appropriation and land use.
      PubDate: 2017-01-30T06:10:47.856949-05:
      DOI: 10.1111/1365-2745.12726
       
  • 28-year temporal sequence of epidemic dynamics in a natural
           rust–host plant metapopulation
    • Authors: Lars Ericson; Warren J. Müller, Jeremy J. Burdon
      Abstract: A long-term study of disease dynamics caused by the rust Uromyces valerianae in 31 discrete populations of Valeriana salina provides a rare opportunity to explore extended temporal patterns in the epidemiology of a natural host–pathogen metapopulation.Over a 28-year period, pathogen population dynamics varied across the metapopulation with disease incidence (presence/absence), prevalence (% plants infected) and severity (% leaf area covered by lesions) all showing strong population and year effects, indicative of heterogeneity among years and host populations in the suitability of conditions for the pathogen.Disease incidence within individual host populations was significantly affected by host population size, disease prevalence the previous year and the proximity of neighbouring populations infected in the current year. After accounting for these variables there was still a marked temporal component with winter sea level having a significant effect; as did summer rainfall in the second part of the study period (1997–2011).Disease prevalence was also effected by host population size and disease prevalence in the previous year. However, it was less affected by spatial aspects of disease spread than was disease incidence. Winter sea level and June rainfall significantly affected disease prevalence.Assessment of disease impact on plant performance found strong variation in disease severity associated with the aspect and positioning of host populations. Plants growing in lower disease environments produced significantly more seeds than those growing in high disease sites.Significant variation in reaction to infection by U. valerianae was detected among plants within four populations and between these different populations.Synthesis. The epidemiology of Uromyces valerianae was highly influenced by host population size, previous disease and distance. After accounting for these factors, there was a clear temporal signal of change in disease incidence linked to winter sea level and summer rainfall. These patterns reinforce the importance of considering interactions in multiple populations over long periods of time in order to obtain a clear picture of the variability in disease-induced selection pressures across time and space. The behaviour of the pathogen fitted that predicted for a metapopulation with considerable asynchrony in epidemiological patterns among demes.The epidemiology of Uromyces valerianae was highly influenced by host population size, previous disease and distance. After accounting for these factors, there was a clear temporal signal of change in disease incidence linked to winter sea level and summer rainfall. These patterns reinforce the importance of considering interactions in multiple populations over long periods of time in order to obtain a clear picture of the variability in disease-induced selection pressures across time and space. The behaviour of the pathogen fitted that predicted for a metapopulation with considerable asynchrony in epidemiological patterns among demes.
      PubDate: 2017-01-18T04:52:14.401184-05:
      DOI: 10.1111/1365-2745.12720
       
  • Crop-associated virus infection in a native perennial grass: reduction in
           plant fitness and dynamic patterns of virus detection
    • Authors: Helen M. Alexander; Emily Bruns, Hayley Schebor, Carolyn M. Malmstrom
      Abstract: To understand the eco-evolutionary significance of plant viruses in nature, we must (i) quantify the effects of infection on plant fitness and (ii) recognize that native plants are increasingly exposed to crop-associated viruses. Studies of perennials are particularly needed: most of our knowledge of plant-virus interactions is from annuals, yet long-lived species dominate landscapes. Here we used aster models for life-history analysis and longitudinal measures of plant virus status to evaluate multi-year consequences of crop virus infection in a native perennial.We used Barley yellow dwarf virus acquired from wheat to inoculate seedlings of Panicum virgatum L. (switchgrass), a North American prairie grass. We grew inoculated and mock-inoculated individuals of two ecotypes for 3 years in the field. We measured plant size, infection status and fitness components. Aster modelling provided integrated multi-year measures of fitness.Crop virus inoculation reduced multi-year native plant fitness by 30% over 2 years despite generally asymptomatic infection and evidence of resistance. This reduction was greater than predicted from individual fitness components or most size measures. Ecotypes differed in response, with the lowland ecotype experiencing higher apparent recovery from infection. Virus treatment in the upland ecotype delayed flowering phenology and reduced seed filling.Synthesis. Our use of field experimentation, surveys of plant infection status and aster modelling demonstrates a rigorous and broadly applicable approach for quantifying the effects of viruses and other microbes on multi-year plant fitness. We found that a crop virus had negative multi-year effects on native plant fitness even after infection was no longer detected. Viruses may have substantial effects on native vegetation with domestication of landscapes and agricultural expansion.Field experimentation, surveys of plant infection status and aster modelling provide a rigorous and broadly applicable approach for quantifying the effects of microbes on multi-year plant fitness. We found that a crop virus had negative multi-year effects on native plant fitness even after infection was no longer detected. Viruses may have substantial effects on native vegetation with agricultural expansion.
      PubDate: 2017-01-16T19:00:02.386818-05:
      DOI: 10.1111/1365-2745.12723
       
  • Disruption of plant–soil–microbial relationships influences
           plant growth
    • Authors: Daniel P. Keymer; Richard A. Lankau
      Abstract: Differential dispersal of plant and microbial propagules may result in the geographical disassociation of plant populations from their local abiotic conditions and microbial communities, especially in the face of species introductions and changing climates.To assess the potential consequences of disrupting historical relationships between plant populations, microbial communities and soil conditions, we grew Carpinus caroliniana seedlings from populations across the species range in combinations of sterilized soils and soil microbial communities, in soils collected from sites with or without conspecific trees. This controlled environment study simulated the consequences for seedling growth of independently or jointly disrupting the historical plant population–soil match, plant population–microbial community match and microbial community–soil match.Seedlings grown in soils from areas without conspecifics had lower biomass, but benefited from inoculation with their historical microbial communities. For conspecific-cultured soils, growth was optimized when seedlings grew with novel microbial communities, but only when microbial communities were local with respect to abiotic soil conditions. Correlative evidence suggests that this may stem from alignment of ectomycorrhizal fungal communities to abiotic soil conditions.Synthesis. Maintaining historical plant–microbial community relationships may benefit plant species spreading into new areas; however, for movement within current ranges, maintaining the historical relationship between microbial communities and the abiotic aspects of soils may have more important consequences for early growth.Maintaining historical plant–microbial community relationships may benefit plant species spreading into new areas; however, for movement within current ranges, maintaining the historical relationship between microbial communities and the abiotic aspects of soils may have more important consequences for early growth.
      PubDate: 2017-01-16T10:50:27.159884-05:
      DOI: 10.1111/1365-2745.12716
       
  • Genotypic diversity mitigates negative effects of density on plant
           performance: a field experiment and life cycle analysis of common evening
           primrose Oenothera biennis
    • Authors: Susan C. Cook-Patton; Amy P. Hastings, Anurag A. Agrawal
      Abstract: Genotypic diversity in plant populations is known to enhance plant performance and ecosystem function. Nonetheless, the effect of genotypic diversity has rarely been examined across a population's lifecycle despite the expectation that changing conditions, such as population density, will alter the benefits of diversity.We simultaneously manipulated a component of genotypic diversity (richness, the number of genotypes) and density of common evening primrose Oenothera biennis to address the consequences for herbivory and lifetime fitness in a 2-year field experiment that spanned seed germination to lifetime fruit production. We genotyped>1100 seedlings with microsatellite DNA markers to determine realized diversity and density in plots sown with O. biennis seeds. Our design achieved quantitative variation in plant density and diversity, with one to 44 individuals established in field plots and two to eight genotypes per polyculture plot (based on microsatellite analysis of reproductive plants).We found a strong interaction between seed density and genetic diversity, with germination and establishment being 24% higher in genetic polycultures than monocultures, but only at low seed density. At high seed density, the opposite pattern emerged, with polycultures having 12% fewer individuals established than monocultures. Initial effects of emergence on plot density persisted through to the fruiting stage.Higher plant densities resulted in increased mortality, decreased probability of reproduction, decreased plant height and lower levels of lifetime fruit production per plant. Increasing genotypic diversity increased the probability of reproduction overall and showed a significant interaction with plant density mitigating the negative effects of high density on individual height and lifetime fruit production.Synthesis. Plant density and genotypic diversity interacted from the very early stages of seed germination and establishment of Oenothera biennis. This effect persisted over the 2-year life cycle of plants, and genotypic diversity buffered against the negative fitness consequences of high plant density. These results imply a dynamic interplay between the long-held paradigm of density effects in plant ecology and the genetic structure of populations.Plant density and genotypic diversity interacted from the very early stages of seed germination and establishment of Oenothera biennis. This effect persisted over the 2-year life cycle of plants, and genotypic diversity buffered against the negative fitness consequences of high plant density. These results imply a dynamic interplay between the long-held paradigm of density effects in plant ecology and the genetic structure of populations.
      PubDate: 2017-01-16T08:25:34.85315-05:0
      DOI: 10.1111/1365-2745.12717
       
  • Phylogenetic relatedness, phenotypic similarity and plant–soil
           feedbacks
    • Authors: Connor R. Fitzpatrick; Laura Gehant, Peter M. Kotanen, Marc T. J. Johnson
      Abstract: Plant–soil feedbacks contribute to species invasions, the maintenance of biodiversity and climate change impacts on terrestrial ecosystems. Despite their far-reaching importance, we lack a general understanding of the ecological and evolutionary determinants of plant–soil feedbacks.We conducted a large-scale plant–soil feedback experiment using 49 co-occurring plant species from southern Ontario, Canada, representing a wide phylogenetic range. We tested whether the effects of soil conditioning vary among these species and whether different focal species respond similarly to the same soil conditioning. Next, we investigated whether plant traits and soil feedbacks depend on phylogenetic similarity and which plant traits affect plant–soil feedbacks between pairs of plant species. Finally, we used our experimental results to test whether soil feedbacks affect co-occurrence of species in the field.We found evidence of both strong positive and negative soil feedbacks between pairs of plant species. Our soil-conditioning treatment explained nearly 20% of the variation in focal species performance.Phylogenetic relatedness and phenotypic similarity between plant species were unrelated to the strength of their soil feedback. However, numerous plant traits of the conditioning species influenced the strength of soil feedbacks on focal species, including specific leaf area and total above-ground productivity. Trait differences between species were also predictive of plant–soil feedbacks, though for some pairs of species, increased trait differences were associated with positive plant–soil feedbacks and for others, trait differences were associated with negative plant–soil feedbacks.Plant species co-occurrence in the field was related to their experimentally determined soil feedbacks but only for particular plant species.Synthesis. Our results illustrate how evolutionary history and phenotypic variation shape plant–soil feedbacks and highlight the need for trait-based studies. Due to the unique evolutionary history of individual traits and the variability in their importance across all possible interacting species, we show that indices of overall phenotypic and phylogenetic relatedness are poor predictors of plant–soil feedbacks at large phylogenetic scales. We conclude that a detailed trait-based approach can be used to predict plant–soil feedbacks, and laboratory measures of soil feedbacks can explain patterns of co-occurrence in nature.Our results illustrate how evolutionary history and phenotypic variation shape plant–soil feedbacks and highlight the need for trait-based studies. Due to the unique evolutionary history of individual traits and the variability in their importance across all possible interacting species, we show that indices of overall phenotypic and phylogenetic relatedness are poor predictors of plant–soil feedbacks at large phylogenetic scales. We conclude that a detailed trait-based approach can be used to predict plant–soil feedbacks, and laboratory measures of soil feedbacks can explain patterns of co-occurrence in nature.
      PubDate: 2017-01-13T05:40:45.293044-05:
      DOI: 10.1111/1365-2745.12709
       
  • Small-scale and regional spatial dynamics of an annual plant with
           contrasting sexual systems
    • Authors: Marcel E. Dorken; Robert P. Freckleton, John R. Pannell
      Abstract: Plant demography is known to depend on both spatial dynamics and life history, but how these two factors interact is poorly understood. We conducted a longitudinal study of the wind-pollinated annual plant Mercurialis annua that varies geographically in its sexual system to investigate this interaction.Metapopulation demographic models predict that regular population turnover should be a more common feature of monomorphic than dimorphic populations because males and females cannot found new populations by selfing but hermaphrodites can. We tested the prediction that rates of population turnover would be higher in monomorphic compared to dimorphic regions.We surveyed 356 populations of M. annua along five regional transects in Morocco and the Iberian Peninsula over a 3-year period to examine their demography and persistence. Each transect crossed a transition in the sexual system, from a monomorphic region where almost all populations were hermaphroditic to a dimorphic one in which most populations had separate sexes (males with females or hermaphrodites).As predicted, rates of local apparent extinctions (i.e., the disappearance of adult plants) were nearly 50% higher in monomorphic compared to dimorphic regions. Local extinctions appeared to be driven by changes in vegetation cover, with extinctions tending to occur in sites in which perennial cover also declined. This suggests that disturbance is a primary agent of local extinctions.We further examined the influence of regional dynamics on local demographic properties by investigating patterns of spatial autocorrelation in population density across years. We found positive spatial autocorrelations in plant densities within regions for both sexual systems. However, these positive autocorrelations extended over shorter distances in monomorphic regions, perhaps as a result of greater population flux in these regions.Synthesis. Our study shows that population dynamics may be influenced by processes acting at a range of spatial scales: within patches, across patches within sites, and across sites within regions, as well as by life-history variation. In Mercurialis annua, regional variation in apparent extinction rates is affected by life history and implicated in regulating the geographical distribution of populations with different sexual systems.Our study shows that population dynamics may be influenced by processes acting at a range of spatial scales: within patches, across patches within sites, and across sites within regions, as well as by life-history variation. In Mercurialis annua, regional variation in apparent extinction rates is affected by life history and implicated in regulating the geographical distribution of populations with different sexual systems.
      PubDate: 2017-01-09T09:00:36.295307-05:
      DOI: 10.1111/1365-2745.12719
       
  • Herbivore size matters for productivity–richness relationships in
           African savannas
    • Authors: Deron E. Burkepile; Richard W. S. Fynn, Dave I. Thompson, Nathan P. Lemoine, Sally E. Koerner, Stephanie Eby, Nicole Hagenah, Kevin R. Wilcox, Scott L. Collins, Kevin P. Kirkman, Alan K. Knapp, Melinda D. Smith
      Abstract: Productivity and herbivory often interact to shape plant community composition and species richness with levels of production mediating the impact of herbivory. However, differences in herbivore traits such as size, feeding guild and dietary requirements may result in different impacts of diverse herbivore guilds across productivity gradients.We used size-selective herbivore exclosures to separate the effects of herbivory by larger herbivores, such as elephant, Burchell's zebra and blue wildebeest from those of medium/smaller herbivores, such as impala and warthog, on herbaceous plant communities. These exclosures were established along a 10-fold productivity gradient, ranging from 90 to 950 g m−2 of standing plant biomass in the Kruger National Park, South Africa.Exclusion of all herbivores generally increased plant species richness at low productivity, but decreased richness at high productivity. Exclusion of medium/smaller herbivores (e.g. impala, warthog) showed stronger effects on plant richness, particularly loss of forbs, at higher productivity rather than at lower productivity. In contrast, exclusion of larger herbivores had stronger effects on plant richness, typically with increasing forb richness, at low rather than high productivity.The change in species richness appeared linked to changes in light availability following herbivore exclusion. Strong increases in shading led to declines in species richness while more moderate increases in shading led to increases in species richness, possibly due to amelioration of heat and water stress by modest increases in shading.Increasing plant dominance, which likely alters multiple mechanisms of plant interactions, was correlated with declines in plant richness following herbivore exclusion. The impact of increasing dominance on plant richness operated independent of productivity, with the exclusion of impala appearing particularly important in driving this relationship.Synthesis. We show that the impact of herbivore losses on plant diversity will be strongly situation dependent and will vary with the herbivores lost (e.g. larger vs. smaller, grazers vs. browsers), plant functional type (e.g. grasses vs. forbs) and environmental context (e.g. productivity). Although larger herbivores are often emphasized for their strong impacts on community dynamics and ecosystem processes, we show that smaller, abundant herbivores can exert strong top-down control on plant communities.In an African savanna, we show that the impact of herbivore losses on plant diversity depends on herbivore type (e.g. larger vs. smaller, grazers vs. browsers), plant functional group (e.g. grasses vs. forbs) and productivity. Although larger herbivores such as elephant, buffalo and zebra often have strong impacts on community dynamics, we show that smaller, abundant herbivores such as impala can exert strong top-down control on plant communities.
      PubDate: 2017-01-09T08:56:00.462166-05:
      DOI: 10.1111/1365-2745.12714
       
  • Precipitation mediates the effect of human disturbance on the Brazilian
           Caatinga vegetation
    • Authors: Kátia F. Rito; Víctor Arroyo-Rodríguez, Rubens T. Queiroz, Inara R. Leal, Marcelo Tabarelli
      Abstract: Seasonally dry tropical forests (SDTFs) are one of the most threatened forests world-wide. These species-rich forests not only cope with several acute (e.g. forest loss) and chronic (e.g. overgrazing and firewood extraction) human disturbances but also with climate change (e.g. longer and more severe droughts); yet, the isolated and combined effects of climate and acute and chronic human disturbances on SDTF vegetation are poorly known.Given the environmental filter imposed by drought in SDTFs, the composition and structure of vegetation is expected to be strongly associated with annual precipitation, and thus the effects of human disturbances on vegetation may also depend on precipitation (i.e. interacting effect).We tested these hypotheses in the Brazilian Caatinga – a SDTF threatened by climate change and human disturbances. We evaluated the isolated and combined (both additive and multiplicative) effect of precipitation, a chronic disturbance index and acute disturbance (landscape forest cover) on the diversity, stem density, evenness, taxonomic composition and above-ground biomass of adult trees and shrubs across 19 0·1-ha plots distributed along a disturbance and precipitation gradients.We recorded 5541 stems from 129 species. Precipitation showed a stronger (positive) effect on species diversity than acute and chronic disturbances and, as expected, the effect of disturbance depended on precipitation (interacting effect): that is, species diversity (especially the number of rare species) was negatively related to forest loss but positively related to chronic disturbance in wetter sites, whereas in drier sites, species diversity was weakly related to forest cover, but strongly and negatively related to chronic disturbance. Contrary to species diversity, community evenness, stem density and biomass were weakly related to all predictors.Synthesis. Precipitation appears to be a strong environmental filter determining the distribution of water-demanding plant species. Chronic disturbance in wetter (high-productive) forests may favour species diversity by increasing ecosystem heterogeneity (intermediate disturbance hypothesis). Yet, the biodiversity costs of chronic disturbance are higher in drier (low-productive) forests; that is, there is a co-limitation imposed by drought and disturbance in drier forests. Overall, our findings indicate that rapid climatic changes in the region will probably have strong negative effects on this seasonally dry tropical forest.Precipitation appears to be a strong environmental filter determining the distribution of water-demanding plant species. Chronic disturbance in wetter (high-productive) forests may favour species diversity by increasing ecosystem heterogeneity (intermediate disturbance hypothesis). Yet, the biodiversity costs of chronic disturbance are higher in drier (low-productive) forests; that is, there is a co-limitation imposed by drought and disturbance in drier forests. Overall, our findings indicate that rapid climatic changes in the region will probably have strong negative effects on this SDTF.
      PubDate: 2017-01-05T04:51:07.288582-05:
      DOI: 10.1111/1365-2745.12712
       
  • Decade-long time delays in nutrient and plant species dynamics during
           eutrophication and re-oligotrophication of Lake Fure 1900–2015
    • Authors: Kaj Sand-Jensen; Hans Henrik Bruun, Lars Baastrup-Spohr
      Abstract: A central topic in nature conservation and ecological restoration is the potential of ecosystems to recover after the reduction of negative anthropogenic impacts. Often, protracted delays in biotic response to abiotic change have been observed.We analysed a unique long-term data series in Lake Fure, Denmark, spanning the transformation from pristine environmental conditions in the early 1900s through a period (1920–1970) of eutrophication – from accelerating sewage input of phosphorus (P) – and subsequent re-oligotrophication after sewage cleaning (1970–2015). We examine time delays between P inputs, in-lake P concentrations and the richness and composition of submerged macrophyte communities.Lake P concentration exhibited decade-long delays in response to periods of increasing or decreasing P inputs. It took 40 years and a 25-fold increase in P input before P concentrations suddenly took off in the 1960s, reflecting profound sediment accumulation. Following reduced P input from c. 1970, it took 5 years before P concentrations showed the first signs of a decline. In 2014, water P concentration was still markedly higher than in 1931, despite much lower P inputs, because of elevated sediment release.Fifty years of eutrophication led to a reduction in aquatic macrophyte richness from 36 species to 12. Species’ responses were closely related to their growth strategy and depth distribution. Deep-growing mosses, charophytes and short angiosperms disappeared, while tall angiosperms survived and pollution-tolerant macroalgae colonized and spread. Subsequently, 45 years of oligotrophication led to clearer waters, macrophyte richness recovering to 28 species and some charophytes and short angiosperms reappearing. Dominance of pollution-tolerant macroalgae persisted, however. Change in species dominance takes longer than colonization by new species.Synthesis. Time delays of P concentrations, water clarity and macrophyte richness and composition were long and complex. Neglecting growth strategies of species makes application of extinction debt and colonization credit concepts dubious, because numbers of oligotrophic species decrease and eutrophic species increase concomitantly during eutrophication and vice versa during oligotrophication. Although the original high species richness may be attained, it is unlikely that the original species composition is restored because many oligotrophic species have vanished from the regional species pool.Time delays of P concentrations, water clarity and macrophyte richness and composition were long and complex. Neglecting growth strategies of species makes application of extinction debt and colonization credit concepts dubious, because numbers of oligotrophic species decrease and eutrophic species increase concomitantly during eutrophication and vice versa during oligotrophication. Although the original high species richness may be attained, it is unlikely that the original species composition is restored because many oligotrophic species have vanished from the regional species pool.
      PubDate: 2017-01-04T08:20:24.4736-05:00
      DOI: 10.1111/1365-2745.12715
       
  • Plant litter mixture partly mitigates the negative effects of extended
           drought on soil biota and litter decomposition in a Mediterranean oak
           forest
    • Authors: Mathieu Santonja; Catherine Fernandez, Magali Proffit, Charles Gers, Thierry Gauquelin, Ilja M. Reiter, Wolfgang Cramer, Virginie Baldy
      Abstract: A major challenge of current ecological research is to determine the responses of plant and animal communities and ecosystem processes to future environmental conditions. Ecosystems respond to climate change in complex ways, and the outcome may significantly depend on biodiversity.We studied the relative effects of enhanced drought and of plant species mixture on soil biota and on litter decomposition in a Mediterranean oak forest. We experimentally reduced precipitation, accounting for seasonal precipitation variability, and created a single-species litter (Quercus pubescens), a two-species litter mixture (Q. pubescens + Acer monspessulanum) and a three-species litter mixture (Q. pubescens + A. monspessulanum + Cotinus coggygria).In general, drier conditions affected decomposers negatively, directly by reducing fungal biomass and detritivorous mesofauna, and also indirectly by increasing the predation pressure on detritivorous mesofauna by predatory mesofauna. This is reflected under drier conditions in that Collembola abundance decreased more strongly than Acari abundance. One Collembola group (i.e. Neelipleona) even disappeared completely.Increased drought strongly decreased litter decomposition rates. Mixed litter with two and three plant species positively affected soil biota communities and led to a more efficient litter decomposition process, probably through a greater litter quality. Faster decomposition in mixed litter can thus compensate slower decomposition rates under drier condition.Synthesis. Our results highlight that, within our study system, drier climate strongly impacts on soil biodiversity and hence litter decomposition. Species-rich litter may mitigate such a decline in decomposition rates. Diverse plant communities should hence be maintained to reduce shifts in ecosystem functioning under climate change.We studied the relative effects of aggravated drought and of plant species mixture on soil biota and on litter decomposition in a Mediterranean oak forest. Drier climate strongly reduced soil biodiversity and litter decomposition rates. However, species-rich litter partly mitigated such a decline. Diverse plant communities should hence be maintained to reduce shifts in ecosystem functioning under climate change.
      PubDate: 2017-01-04T06:05:33.657481-05:
      DOI: 10.1111/1365-2745.12711
       
  • Community transcriptomics, genomics and the problem of species
           co-occurrence
    • Authors: Nathan G. Swenson; F. Andrew Jones
      Pages: 563 - 568
      Abstract: Genomic and transcriptomic information has been largely leveraged in ecological investigations of primarily model species and their relatives. The amount of infrastructure and financing necessary for such investigations has meant that analyses of assemblages full of non-model species were impossible. These barriers have rapidly eroded over the past few years to the point where community ecology will soon see a large influx of genomic and transcriptomic investigations. The hope is that such studies will greatly refine or even transform our inferences regarding the distribution and co-occurrence of plant species.This special feature presents five studies that use cutting-edge ‘omic concepts and approaches in assemblages of non-model species. All studies focus on the drivers of species co-occurrence. The work blends functional phylogenomic, differential gene expression and metagenomic approaches in observational and experimental frameworks.Two studies demonstrate of functional phylogenomic approaches that can be used in conjunction with neighbourhood demographic models to understand the role of neighbouring heterospecific species on focal tree demography. Two additional papers demonstrate how genes are differentially expressed in different competitive contexts and how this is related to species coexistence. The final study uses a metabarcoding approach to document whether the incredible levels of soil fungal and tree biodiversity in the tropics are linked.Synthesis. The articles presented in this special feature clearly demonstrate that ‘omic toolkits can now be readily integrated into community ecology. While there are still many obstacles facing this integration, it seems clear that the amounts and types of data provided by such approaches will lead to a rapid transformation in how we study plant communities.
      PubDate: 2017-04-16T23:03:22.359064-05:
      DOI: 10.1111/1365-2745.12771
       
  • The role of soil chemistry and plant neighbourhoods in structuring fungal
           communities in three Panamanian rainforests
    • Authors: Tyler Schappe; Felipe E. Albornoz, Benjamin L. Turner, Abigail Neat, Richard Condit, F. Andrew Jones
      Pages: 569 - 579
      Abstract: Fungi play critical roles in ecosystem processes and interact with plant communities in mutualistic, pathogenic, and commensal ways. Fungal communities are thought to depend on both associated tree communities and soil properties. However, the relative importance of the biotic and abiotic drivers of soil fungal community structure and diversity in lowland tropical forests remains poorly understood.We examined the community structure of trees and fungi at different levels of phosphorus (0·17–16·3 mg kg−1) in moist tropical forests in Panama. We predicted that arbuscular mycorrhizal (AM) fungal composition would be more strongly associated with soil properties than with local tree communities while the composition of other fungal clades would be more strongly correlated with local tree communities than soil properties. We also predicted that fungal operational taxonomic unit (OTU) richness would be negatively correlated with soil fertility and positively correlated with tree species diversity within and among forests.We characterized soil chemistry, fine root biomass, and sequenced the ITS1 barcode region to describe fungal community composition from 70 soil cores across three 1-ha tropical rainforest sites in Panama. The sites vary in soil chemistry, including P, and in tree species community composition, but experience similar annual rainfall.AM fungal community composition was partially correlated with soil chemistry (r = 0·32, P ≤ 0·001), but not with local tree communities, while non-AM fungal communities were nearly equally correlated with soil chemistry (Partial Mantel test, r = 0·38, P ≤ 0·001) as with tree communities (r = 0·36, P ≤ 0·001). Linear models showed that AM OTU richness was not explained by any independent variable. For non-AM fungi, phosphorus, pH, and soil moisture better predicted OTU richness across all cores than other biotic and abiotic factors.Synthesis. Our results show that AM fungal structure is driven primarily by soil chemistry. For non-AM fungi, soil properties and the local tree community can play a joint role in structuring communities. Furthermore, we found that more diverse local tree communities did not harbour more fungal species. Our results suggest that soil properties act as an environmental filter for both trees and fungi, setting the stage for interactions between the two.Our results show that AM fungal structure is driven primarily by soil chemistry. For non-AM fungi, soil properties and the local tree community can play a joint role in structuring communities. Furthermore, we found that more diverse local tree communities did not harbour more fungal species. Our results suggest that soil properties act as an environmental filter for both trees and 4 fungi, setting the stage for interactions between the two.
      PubDate: 2017-04-16T23:03:17.176908-05:
      DOI: 10.1111/1365-2745.12752
       
  • Ecological interactions and coexistence are predicted by gene expression
           similarity in freshwater green algae
    • Authors: Anita Narwani; Bastian Bentlage, Markos A. Alexandrou, Keith J. Fritschie, Charles Delwiche, Todd H. Oakley, Bradley J. Cardinale
      Pages: 580 - 591
      Abstract: Phenotypic variation controls the species interactions which determine whether or not species coexist. Long-standing hypotheses in ecology and evolution posit that phenotypic differentiation enables coexistence by increasing the size of niche differentiation. This hypothesis has only been tested using macroscopic traits to date, but niche differentiation, particularly of microscopic organisms, also occurs at the molecular and metabolic level.We examined how phenotypic variation that arises at the level of gene expression over evolutionary time affects phytoplankton species interactions and coexistence.We predicted that similarity in gene expression among species would decline with phylogenetic distance, and that reduced similarity in gene expression would weaken competition, increase facilitation and promote coexistence.To test this, we grew eight species of freshwater green algae in monocultures and bicultures for 46 days in a laboratory microcosm experiment. We quantified the strength of species interactions by: (i) fitting Lotka–Volterra models to time-series densities and estimating interaction coefficients, and (ii) calculating relative densities that compare species’ steady-state densities in biculture to those in monoculture. We used Illumina high throughput sequencing to quantify the expression of 1253 families of homologous genes, including a set of 17 candidate genes that we hypothesized a priori to be involved in competition or facilitation.Synthesis. We found that closely related species had greater similarity in gene expression than did distantly related species, but as gene expression became more similar, species experienced weaker competition or greater facilitation, and were more likely to coexist. We identified gene functional categories that were uniquely differentially regulated in association with particular species interaction types. Contrary to common thinking in ecology and evolution, similarity in gene expression, and not differentiation, was associated with weaker competition, facilitation and coexistence.We found that closely related species had greater similarity in gene expression than did distantly related species, but as gene expression became more similar, species experienced weaker competition or greater facilitation, and were more likely to coexist. We identified gene functional categories that were uniquely differentially regulated in association with particular species interaction types. Contrary to common thinking in ecology and evolution, similarity in gene expression, and not differentiation, was associated with weaker competition, facilitation and coexistence.
      PubDate: 2017-04-16T23:03:10.136834-05:
      DOI: 10.1111/1365-2745.12759
       
  • The role of transcriptomes linked with responses to light environment on
           seedling mortality in a subtropical forest, China
    • Authors: Baocai Han; María Natalia Umaña, Xiangcheng Mi, Xiaojuan Liu, Lei Chen, Yunquan Wang, Yu Liang, Wei Wei, Keping Ma
      Pages: 592 - 601
      Abstract: Differences in seedling survival in trees have a lasting imprint on seedling, juvenile and adult community structure. Identifying the drivers of these differences, therefore, is a critical research objective that ultimately requires knowledge regarding how organismal function interacts with the local environment to influence survival rates.In tree communities, differences in light use strategies are frequently invoked to explain differences in seedling demographic performance through growth and survival trade-offs. For example, shade-tolerant species grow slowly and have higher survival rates, whereas shade-intolerant species grow quickly but have lower survival rates. Thus, functional traits related to photosynthesis should be strong predictors of demographic rates, but results in the literature are mixed indicating that additional or alternative information regarding organismal function should be considered.Here, we provide a community-wide inventory of transcriptomes in a subtropical tree community. This information is utilized to determine the degree to which species share homologous genes related to gene ontologies for light use and harvesting. These species similarities are used in neighbourhood generalized linear mixed-effects models of seedling survival that evaluated seedling survival as a function of the transcriptomic, functional trait and phylogenetic composition of the local neighbourhood. The results show neighbourhood similarity in three of the 15 gene ontologies evaluated are significantly related to survival rates based on neighbourhood composition. For two of these ontologies, survival rates increase when neighbours are similar in their gene tree composition indicating the importance of abiotic filtering and performance hierarchies.Synthesis. The present work takes a novel approach by sequencing the transcriptomes of naturally co-occurring tree species in a subtropical forest in China. The results show that the transcriptomic similarity of species is a significant predictor of differential survival. The study demonstrates that exploring the functional genomic similarity of non-model species in nature has the potential to increase the breadth and depth of our understanding of how gene function influences species co-occurrence and population dynamics in communities.The present work takes a novel approach by sequencing the transcriptomes of naturally co-occurring tree species in a subtropical forest in China. The results show that the transcriptomic similarity of species is a significant predictor of differential survival. The study demonstrates that exploring the functional genomic similarity of non-model species in nature has the potential to increase the breadth and depth of our understanding of how gene function influences species co-occurrence and population dynamics in communities.
      PubDate: 2017-04-16T23:03:23.114679-05:
      DOI: 10.1111/1365-2745.12760
       
  • Transcriptomic responses to conspecific and congeneric competition in
           co-occurring Trifolium
    • Authors: Alan W. Bowsher; Prateek Shetty, Brian L. Anacker, Andrew Siefert, Sharon Y. Strauss, Maren L. Friesen
      Pages: 602 - 615
      Abstract: Species coexistence requires differential response to inter- and intraspecific competition, typically conceptualized as niche differentiation. Coexistence of close relatives therefore poses an interesting scenario with regards to niche differentiation since these species generally have many traits in common due to shared ancestry. Native Californian Trifolium assemblages are locally diverse and represent a unique system for understanding competitive interactions among close relatives.We conducted two similar greenhouse studies in which Trifolium fucatum was grown alone, with a conspecific competitor, and with a congeneric competitor (Trifolium macraei). In the first study, we assessed biomass production in T. fucatum, and in the second study we conducted an RNAseq analysis of T. fucatum roots to test for differentially expressed genes that may mediate competitive interactions and potentially coexistence.Compared to plants grown alone, competition (i.e. growth in the same pot) with a conspecific resulted in a greater reduction in biomass than competition with a congener, as predicted by theory. However, competition with a congener resulted in twice as many differentially expressed genes as competition with a conspecific.Annotations of identified genes differentiating congeneric from conspecific competition suggest several functions attributed to interactions with third-party organisms, including nodulation with rhizobial mutualists, and defence responses against pathogens and herbivores. In addition, salt-responsive genes and an iron transporter were differentially expressed in congeneric competition, and comparisons of sodium and iron concentrations in field soils where these species are found showed that T. fucatum occurs in higher sodium and iron microsites than T. macraei. Thus, the transcriptome highlighted abiotic niche axes worth pursuing in future ecological experiments as potential mediators of coexistence.We also found a subset of genes that responded similarly to both congeneric and conspecific competition in both direction and magnitude, indicating some conserved responses to competition, regardless of neighbour identity.Synthesis. Transcriptomic analyses represent novel tools for identifying the molecular mechanisms underlying interactions among species. Working iteratively with ecological experimentation and observation, transcriptomes may allow us to identify novel dimensions of the n-dimensional niche that determine species’ distributions and their ability to coexist.Trifolium fucatum plants showed differential root gene expression that was greater when grown under competition with Trifolium macraei than under conspecific competition, despite conspecifics having a greater impact on growth. Genes with contrasting expression patterns suggest important niche differences include ‘third-party’ interactions, salinity, and iron, matching field data that species prefer contrasting sodium and iron microsites.
      PubDate: 2017-04-16T23:03:20.855193-05:
      DOI: 10.1111/1365-2745.12761
       
  • Neighbourhood defence gene similarity effects on tree performance: a
           community transcriptomic approach
    • Authors: Jenny Zambrano; Yoshiko Iida, Robert Howe, Luxiang Lin, Maria Natalia Umana, Amy Wolf, Samantha J. Worthy, Nathan G. Swenson
      Pages: 616 - 626
      Abstract: The structure and dynamics of ecological communities are ultimately the outcome of the differential demographic rates of individuals. Individual growth and mortality rates largely result from the interaction between an organism's phenotype and the abiotic and biotic environment. Functional traits have been used extensively over the past decade to elucidate links among phenotypes, demography and community dynamics.A fundamental weakness of most functional trait approaches is the use of ‘soft’ traits associated with resource acquisition to examine how neighbourhood similarity affects tree survival and growth. However, these ‘soft’ traits are unlikely to be good predictors of similarities among co-occurring species. Less easily measured aspects of organismal function – such as those related to defence – have frequently gone unmeasured. This is particularly problematic for testing important hypotheses in forest ecology, such as the Janzen–Connell hypothesis where focal trees are expected to be at a disadvantage if their neighbours share the same natural enemies.A potential alternative to functional trait approaches is to quantify the transcriptomic or functional genomic similarity of species. Such analyses are now possible in natural systems where de novo transciptome assemblies can be used to conduct functional phylogenomic analyses where homologous gene trees are produced. Using demographic plot data for 21 species from a North American forest dynamic plot, we conduct a community functional phylogenomic analysis of a plant community to elucidate the similarity in defence response genes across species. This similarity was then used to ask whether the similarity in defence genes of heterospecific species in the local neighbourhood of a focal individual tree influences its growth and mortality rates.The results show that individual growth rates are higher when surrounded by dissimilar heterospecific species for 16 of 27 defence genes analysed. Additionally, survival rates are increased when an individual is in a neighbourhood with dissimilar species for 4 of the 27 defence genes studied. Lastly, strong conspecific effects were found in all analyses, underscoring that future analyses investigating the genetic variation and differential expression of defence-related genes in neighbourhoods may prove important.Synthesis. In summary, this research leverages recent advances in RNA sequencing and bioinformatics to conduct community-wide transcriptomic analyses and analyses of defence-related gene similarity across a tree community. The results demonstrate that defence gene similarity in neighbourhoods often does have negative effects on individual demographic performance as predicted by the Janzen–Connell hypothesis.In summary, this research leverages recent advances in RNA sequencing and bioinformatics to conduct community-wide transcriptomic analyses and analyses of defence-related gene similarity across a tree community. The results demonstrate that defence gene similarity in neighbourhoods often does have negative effects on individual demographic performance as predicted by the Janzen-Connell hypothesis.
      PubDate: 2017-04-16T23:03:21.464184-05:
      DOI: 10.1111/1365-2745.12765
       
  • Herbivore size matters for productivity-richness relationships in African
           savannas: Commentary on Burkepile et al. (2017)
    • Authors: Elisabeth S. Bakker
      Pages: 687 - 689
      PubDate: 2017-04-16T23:03:13.196286-05:
      DOI: 10.1111/1365-2745.12745
       
 
 
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