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Bacterial and fungal root endophytes can impact the fitness of their host plants, but the relative importance of drivers for root endophyte communities is not well known. Host plant species, the composition and density of the surrounding plants, space, and abiotic drivers could significantly affect bacterial and fungal root endophyte communities. We investigated their influence in endophyte communities of alpine plants across a harsh high mountain landscape using high-throughput sequencing. There was less compositional overlap between fungal than bacterial root endophyte communities, with four ‘cosmopolitan’ bacterial OTUs found in every root sampled, but no fungal OTUs found across all samples. We found that host plant species, which included nine species from three families, explained the greatest variation in root endophyte composition for both bacterial and fungal communities. We detected similar levels of variation explained by plant neighborhood, space, and abiotic drivers on both communities, but the plant neighborhood explained less variation in fungal endophytes than expected. Overall, these findings suggest a more cosmopolitan distribution of bacterial OTUs compared to fungal OTUs, a structuring role of the plant host species for both communities, and largely similar effects of the plant neighborhood, abiotic drivers, and space on both communities.

Climate change is increasing the variability of precipitation, altering the frequency of soil drying-wetting events and the distribution of seasonal precipitation. These changes in precipitation can alter nitrogen (N) cycling and stimulate nitric oxide (NO) emissions (an air pollutant at high concentrations), which may vary according to legacies of past precipitation and represent a pathway for ecosystem N loss. To identify whether precipitation legacies affect NO emissions, we excluded or added precipitation during the winter growing season in a Pinyon-Juniper dryland and measured in-situ NO emissions following experimental wetting. We found that the legacy of both excluding and adding winter precipitation increased NO emissions early in the following summer; cumulative NO emissions from the winter precipitation exclusion plots (2750 ± 972 μg N-NO m

Plant species can show considerable morphological and functional variation along environmental gradients. This intraspecific trait variation (ITV) can have important consequences for community assembly, biotic interactions, ecosystem functions and responses to global change. However, directly measuring ITV across many species and wide geographic areas is often infeasible. Thus, a method to predict spatial variation in a species’ functional traits could be valuable. We measured specific leaf area (SLA), height and leaf area (LA) of grasses across California, covering 59 species at 230 sampling locations. We asked how these traits change along climate gradients within each species and used machine learning to predict local trait values for any species at any location based on phylogenetic position, local climate and that species’ mean traits. We then examined how much these local predictions alter patterns of assemblage-level trait variation across the state. Most species exhibited higher SLA and grew taller at higher temperatures and produced larger leaves in drier conditions. The random forests predicted spatial variation in functional traits very accurately, with correlations up to 0.97. Because trait records were spatially biased towards warmer areas, and these areas tend to have higher SLA individuals within each species, species means of SLA were upwardly biased. As a result, using species means over-estimates SLA in the cooler regions of the state. Our results also suggest that height may be substantially under-predicted in the warmest areas. Synthesis. Using only species mean traits to characterize the functional composition of communities risks introducing substantial error into trait-based estimates of ecosystem properties including decomposition rates or NPP. The high performance of random forests in predicting local trait values provides a way forward for estimating high-resolution patterns of ITV without a massive data collection effort.

Despite the importance of biodiversity-ecosystem functioning (BEF) relationships in ecology and conservation, relatively little is known about how BEF relationships change across spatial scales. Theory predicts that change in BEF relationships with increasing spatial scale will depend on variation in species composition across space (β-diversity), but empirical evidence for this is limited. Moreover, studies have not quantified the direct and indirect role the environment plays in costructuring ecosystem functioning across spatial scales. We used 14 temperate-forest plots 1.4 ha in size containing 18,323 trees to quantify scale-dependence between aboveground tree biomass and three components of tree-species diversity-α-diversity (average local diversity), γ-diversity (total diversity), and β-diversity. Using structural-equation models, we quantified the direct effects of each diversity component and the environment (soil nutrients and topography), as well as indirect effects of the environment, on tree biomass across 11 spatial extents ranging from 400 to 14,400 m

Author(s): Hulshof, CM; Spasojevic, MJ | Abstract: Background: The central thesis of plant ecology is that climate determines the global distribution of vegetation. Within a vegetation type, however, finer-scale environmental features, such as the physical and chemical properties of soil (edaphic variation), control patterns of plant diversity and distributions. Aims: Here, we review the literature to provide a mechanistic framework for the edaphic control of plant diversity. First, we review three examples where soils have known, prevalent effects on plant diversity: during soil formation, on unusual soils and in regions with high edaphic heterogeneity. Second, we synthesize how edaphic factors mediate the relative importance of the four key processes of community assembly (speciation, ecological drift, dispersal and niche selection). Third, we review the potential effects of climate change in edaphically heterogeneous regions. Finally, we outline key knowledge gaps for understanding the edaphic control of plant diversity. In our review, we emphasize floras of unusual edaphic areas (i.e., serpentine, limestone, granite), because these areas contribute disproportionately to the biodiversity hotspots of the world. Taxa: Terrestrial plants. Location: Global. Conclusion: Edaphic variation is a key driver of biodiversity patterns and influences the relative importance of speciation, dispersal, ecological drift, niche selection and interactions among these processes. Research is still needed to gain a better understanding of the underlying mechanisms by which edaphic variation influences these community assembly processes, and unusual soils provide excellent natural systems for such tests. Furthermore, the incorporation of edaphic variation into climate change research will help to increase the predictive power of species distribution models, identify potential climate refugia and identify species with adaptations that buffer them from climate change.

Climate strongly shapes plant diversity over large spatial scales, with relatively warm and wet (benign, productive) regions supporting greater numbers of species. Unresolved aspects of this relationship include what causes it, whether it permeates to community diversity at smaller spatial scales, whether it is accompanied by patterns in functional and phylogenetic diversity as some hypotheses predict, and whether it is paralleled by climate-driven changes in diversity over time. Here, studies of Californian plants are reviewed and new analyses are conducted to synthesize climate–diversity relationships in space and time. Across spatial scales and organizational levels, plant diversity is maximized in more productive (wetter) climates, and these consistent spatial relationships are mirrored in losses of taxonomic, functional, and phylogenetic diversity over time during a recent climatic drying trend. These results support the tolerance and climatic niche conservatism hypotheses for climate–diversity relationships, and suggest there is some predictability to future changes in diversity in water-limited climates.

Arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) are two fungal groups that colonize plant roots and can benefit plant growth, but little is known about their landscape distributions. We performed sequencing and microscopy on a variety of plants across a high-elevation landscape featuring plant density, snowpack, and nutrient gradients. Percent colonization by both AMF and DSE varied significantly among plant species, and DSE colonized forbs and grasses more than sedges. AMF were more abundant in roots at lower elevation areas with lower snowpack and lower phosphorus and nitrogen content, suggesting increased hyphal recruitment by plants to aid in nutrient uptake. DSE colonization was highest in areas with less snowpack and higher inorganic nitrogen levels, suggesting an important role for these fungi in mineralizing organic nitrogen. Both of these groups of fungi are likely to be important for plant fitness and establishment in areas limited by phosphorus and nitrogen.

Plant diversity varies immensely over large-scale gradients in temperature, precipitation, and seasonality at global and regional scales. This relationship may be driven in part by climatic variation in the relative importance of abiotic and biotic interactions to the diversity and composition of plant communities. In particular, biotic interactions may become stronger and more host specific with increasing precipitation and temperature, resulting in greater plant species richness in wetter and warmer environments. This hypothesis predicts that the many defensive compounds found in plants’ metabolomes should increase in richness and decrease in interspecific similarity with precipitation, temperature, and plant diversity. To test this prediction, we compared patterns of chemical and morphological trait diversity of 140 woody plant species among seven temperate forests in North America representing 16.2°C variation in mean annual temperature (MAT), 2,115 mm variation in mean annual precipitation (MAP), and from 10 to 68 co-occurring species. We used untargeted metabolomics methods based on data generated with liquid chromatography-tandem mass spectrometry to identify, classify, and compare 13,480 unique foliar metabolites and to quantify the metabolomic similarity of species in each community with respect to the whole metabolome and each of five broad classes of metabolites. In addition, we compiled morphological trait data from existing databases and field surveys for three commonly measured traits (specific leaf area [SLA], wood density, and seed mass) for comparison with foliar metabolomes. We found that chemical defense strategies and growth and allocation strategies reflected by these traits largely represented orthogonal axes of variation. In addition, functional dispersion of SLA increased with MAP, whereas functional richness of wood density and seed mass increased with MAT. In contrast, chemical similarity of co-occurring species decreased with both MAT and MAP, and metabolite richness increased with MAT. Variation in metabolite richness among communities was positively correlated with species richness, but variation in mean chemical similarity was not. Our results are consistent with the hypothesis that plant metabolomes play a more important role in community assembly in wetter and warmer climates, even at temperate latitudes, and suggest that metabolomic traits can provide unique insight to studies of trait-based community assembly.

Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation-funded Long-Term Ecological Research (LTER) network addressing the core research area of "populations and communities." The objective of this effort was to show the importance of long-term data collection and experiments for addressing the hardest questions in scientific ecology that have significant implications for environmental policy and management. Each LTER site developed at least one compelling case study about what their site could look like in 50-100 yr as human and environmental drivers influencing specific ecosystems change. As the case studies were prepared, five themes emerged, and the studies were grouped into papers in this LTER Futures Special Feature addressing state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the "connectivity" theme and has examples from the Phoenix (urban), Niwot Ridge (alpine tundra), McMurdo Dry Valleys (polar desert), Plum Island (coastal), Santa Barbara Coastal (coastal), and Jornada (arid grassland and shrubland) sites. Connectivity has multiple dimensions, ranging from multi-scalar interactions in space to complex interactions over time that govern the transport of materials and the distribution and movement of organisms. The case studies presented here range widely, showing how land-use legacies interact with climate to alter the structure and function of arid ecosystems and flows of resources and organisms in Antarctic polar desert, alpine, urban, and coastal marine ecosystems. Long-term ecological research demonstrates that connectivity can, in some circumstances, sustain valuable ecosystem functions, such as the persistence of foundation species and their associated biodiversity or, it can be an agent of state change, as when it increases wind and water erosion. Increased connectivity due to warming can also lead to species range expansions or contractions and the introduction of undesirable species. Continued long-term studies are essential for addressing the complexities of connectivity. The diversity of ecosystems within the LTER network is a strong platform for these studies. National Science Foundation Long-Term Ecological Research programNational Science Foundation (NSF) [DEB-1637590, 1832016, DEB-0213767, 0816963, 1354494, 1902712, NSF OCE-0423565, 1058747, 1637630, OPP-1637708, OCE-1232779, DEB-1832194, DEB-1637686] Published version This research was supported by the National Science Foundation Long-Term Ecological Research program grants to the Central Arizona-Phoenix (DEB-1637590, 1832016), Plum Island (DEB-0213767, 0816963, 1354494, 1902712, NSF OCE-0423565, 1058747, 1637630), McMurdo (OPP-1637708), Santa Barbara (OCE-1232779), Jornada (DEB-1832194), and Niwot (DEB-1637686) LTER sites.

Background With 9730 protein-coding genes and a nearly complete gene knockout strain collection, Neurospora crassa is a major model organism for filamentous fungi. Despite this abundance of information, the phenotypes of these gene knockout mutants have not been categorized to determine whether there are broad correlations between phenotype and any genetic features. Results Here, we analyze data for 10 different growth or developmental phenotypes that have been obtained for 1168 N. crassa knockout mutants. Of these mutants, 265 (23%) are in the normal range, while 903 (77%) possess at least one mutant phenotype. With the exception of unclassified functions, the distribution of functional categories for genes in the mutant dataset mirrors that of the N. crassa genome. In contrast, most genes do not possess a yeast ortholog, suggesting that our analysis will reveal functions that are not conserved in Saccharomyces cerevisiae. To leverage the phenotypic data to identify pathways, we used weighted Partitioning Around Medoids (PAM) approach with 40 clusters. We found that genes encoding metabolic, transmembrane and protein phosphorylation-related genes are concentrated in subsets of clusters. Results from K-Means clustering of transcriptomic datasets showed that most phenotypic clusters contain multiple expression profiles, suggesting that co-expression is not generally observed for genes with shared phenotypes. Analysis of yeast orthologs of genes that co-clustered in MAPK signaling cascades revealed potential networks of interacting proteins in N. crassa. Conclusions Our results demonstrate that clustering analysis of phenotypes is a promising tool for generating new hypotheses regarding involvement of genes in cellular pathways in N. crassa. Furthermore, information about gene clusters identified in N. crassa should be applicable to other filamentous fungi, including saprobes and pathogens.

Synthesizing trait observations and knowledge across the Tree of Life remains a grand challenge for biodiversity science. Species traits are widely used in ecological and evolutionary science, and new data and methods have proliferated rapidly. Yet accessing and integrating disparate data sources remains a considerable challenge, slowing progress toward a global synthesis to integrate trait data across organisms. Trait science needs a vision for achieving global integration across all organisms. Here, we outline how the adoption of key Open Science principles—open data, open source and open methods—is transforming trait science, increasing transparency, democratizing access and accelerating global synthesis. To enhance widespread adoption of these principles, we introduce the Open Traits Network (OTN), a global, decentralized community welcoming all researchers and institutions pursuing the collaborative goal of standardizing and integrating trait data across organisms. We demonstrate how adherence to Open Science principles is key to the OTN community and outline five activities that can accelerate the synthesis of trait data across the Tree of Life, thereby facilitating rapid advances to address scientific inquiries and environmental issues. Lessons learned along the path to a global synthesis of trait data will provide a framework for addressing similarly complex data science and informatics challenges.

The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait relationships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world., It is unclear whether plant trait relationships found at the global scale extend to climatic extremes. Here the authors analyse six major aboveground traits to show that known plant trait relationships extend to the tundra biomes and exhibit the same two dimensions of variation detected at the global scale.

International audience; Global climate and land use change are causing woody plant encroachment in arctic, alpine, and arid/semi-arid ecosystems around the world, yet our understanding of the belowground impacts of this phenomenon is limited. We conducted a globally distributed field study of 13 alpine sites across four continents undergoing woody plant encroachment and sampled soils from both woody encroached and nearby herbaceous plant community types. We found that woody plant encroachment influenced soil microbial richness and community composition across sites based on multiple factors including woody plant traits, site level climate, and abiotic soil conditions. In particular, root symbiont type was a key determinant of belowground effects, as Nitrogen-fixing woody plants had higher soil fungal richness, while Ecto/Ericoid mycorrhizal species had higher soil bacterial richness and symbiont types had distinct soil microbial community composition. Woody plant leaf traits indirectly influenced soil microbes through their impact on soil abiotic conditions, primarily soil pH and C:N ratios. Finally, site-level climate affected the overall magnitude and direction of woody plant influence, as soil fungal and bacterial richness were either higher or lower in woody encroached versus herbaceous soils depending on mean annual temperature and precipitation. All together, these results document global impacts of woody plant encroachment on soil microbial communities, but highlight that multiple biotic and abiotic pathways must be considered to scale up globally from site- and species-level patterns. Considering both the aboveground and belowground effects of woody encroachment will be critical to predict future changes in alpine ecosystem structure and function and subsequent feedbacks to the global climate system. © 2020 John Wiley & Sons Ltd

Despite decades of interest, few studies have provided evidence supporting theoretical expectations for coupled relationships between aboveground and belowground diversity and ecosystem functioning in non-manipulated natural ecosystems. We characterized plant species richness and density, soil bacterial, fungal and eukaryotic species richness and phylogenetic diversity (using 16S, ITS, and 18S gene sequencing), and ecosystem function (levels of soil C and N, and rates of microbial enzyme activities) along a natural gradient in plant richness and density in high-elevation, C-deficient soils to examine the coupling between above- and belowground systems. Overall, we observed a strong positive relationship between aboveground (plant richness and density) and belowground (bacteria, fungi, and non-fungal eukaryotes) richness. In addition to the correlations between plants and soil communities, C and N pools, and rates of enzyme activities increased as plant and soil communities became richer and more diverse. Our results suggest that the theoretically expected positive correlation between above- and belowground communities does exist in natural systems, but may be undetectable in late successional ecosystems due to the buildup of legacy organic matter that results in extremely complex belowground communities. In contrast, microbial communities in early successional systems, such as the system described here, are more directly dependent on contemporary inputs from plants and therefore are strongly correlated with plant diversity and density.

Climate warming is a key factor driving species range shifts. While previous work has focused on shifts of aboveground plant communities, changes in climate and vegetation should affect soil communities and hence ecosystem-level nutrient cycling and ecosystem functioning. High alpine ecosystems are particularly sensitive to climate warming because snow is among the main drivers of ecosystem structure and function. Climate-warming snow cover changes at Niwot Ridge in the Colorado Rocky Mountains have resulted in a consistent plant colonization of previously unvegetated soils generating a natural gradient of soil habitats ranging from unvegetated to increasingly vegetated. We used this gradient of plant communities at different successional stages to determine if nematodes respond to climate-driven changes in this high-alpine landscape and if they play a role in changes in soil C and N. We hypothesized that: 1) there would be clear shifts in nematode communities along the gradient as a function of snow cover, plant richness and density, and water holding capacity but that these shifts would be dependent on nematode feeding habits and their positioning in the soil foodweb and 2) the shifts would be associated with accumulating soil C and N. To test these hypotheses, we measured nematodes, plants, and soil microbes, snow cover, pH, soil water holding capacity, and different forms of soil C and N in 98 plots across the plant successional gradient. As predicted, nematode communities exhibited extensive shifts from a few individuals of a single species in unvegetated soils to hundreds of individuals and tens of species within every feeding group under complex plant communities. Representatives of omnivorous and bacterivorous K-strategists preceded plants and plant parasites and root associates depended on plants most. Linear regression models indicated that plants, microbial communities and soil water holding capacity, but not snow cover, were the most predictive factors of nematode diversity and density across all trophic levels and that all nematode groups were positively related to all measures of soil C and N. Structural equation models confirmed these results, but also indicated that effects of climate warming on nematodes were indirect primarily through shifts in plant and microbial communities and changes of soil water holding capacity. Moreover, nematode trophic group densities, but not their diversity, played a potential role in the accumulation of soil N, and to a lesser degree of soil C. Because nematode communities at Niwot Ridge are largely at their early phases of assembly, with continuing climate warming, we predict their increasing abundance and diversity will likely continue, as will their impact on soil C and N processes.

Whether global change will drive changing forests from net carbon (C) sinks to sources relates to how quickly deadwood decomposes. Because complete wood mineralization takes years, most experiments focus on how traits, environments and decomposer communities interact as wood decay begins. Few experiments last long enough to test whether drivers change with decay rates through time, with unknown consequences for scaling short-term results up to long-term forest ecosystem projections. Using a 7 year experiment that captured complete mineralization among 21 temperate tree species, we demonstrate that trait effects fade with advancing decay. However, wood density and vessel diameter, which may influence permeability, control how decay rates change through time. Denser wood loses mass more slowly at first but more quickly with advancing decay, which resolves ambiguity about the after-life consequences of this key plant functional trait by demonstrating that its effect on decay depends on experiment duration and sampling frequency. Only long-term data and a time-varying model yielded accurate predictions of both mass loss in a concurrent experiment and naturally recruited deadwood structure in a 32-year-old forest plot. Given the importance of forests in the carbon cycle, and the pivotal role for wood decay, accurate ecosystem projections are critical and they require experiments that go beyond enumerating potential mechanisms by identifying the temporal scale for their effects.

Aims: It has been well demonstrated that several interacting endogenous and exogenous factors influence decomposition. However, teasing apart the direct and indirect effects of these factors to predict decomposition patterns in heterogenous landscapes remains a key challenge. Methods: At 157 locations in a temperate forest, we measured decomposition of a standard substrate (filter paper) over two years, the landscape context in which decomposition took place, and the functional composition of the woody species that contributed leaf litter to the forest floor where litter bags were placed. We tested for direct and indirect effects of landscape context and direct effects of forest functional composition on decay using structural equation modelling. Results: We found that landscape context had direct effects on decay and indirect effects on decay via its influence on the functional composition of the surrounding forest. Forest functional composition also had direct effects on decay, but these effects decreased or disappeared completely over time. Moreover, community weighted mean trait values were better predictors of decay than functional dispersion of leaf traits, and leaf nitrogen content and carbon content were better predictors of decay than leaf dry matter content or leaf toughness. Conclusions: Our results highlight the importance of an integrative approach that examines the direct and indirect effects of multiple factors for understanding and predicting decomposition patterns across heterogenous landscapes.

Synthesising trait observations and knowledge across the Tree of Life remains a grand challenge for biodiversity science. Despite the well-recognised importance of traits for addressing ecological and evolutionary questions, trait-based approaches still struggle with several basic data requirements to deliver openly accessible, reproducible, and transparent science. Here, we introduce the Open Traits Network (OTN) – a decentralised alliance of international researchers and institutions focused on collaborative integration and standardisation of the exponentially increasing availability of trait data across all organisms. The OTN embraces the use of Open Science principles in trait research, particularly open data, open source, and open methodology protocols and workflows, to accelerate the synthesis of trait data across the Tree of Life. Increased efforts at all levels – from individual scientists, research networks, scientific societies, funding agencies, to publishers – are necessary to fully exploit the opportunities offered by Open Science in trait research. Democratising access to data, tools and resources will facilitate rapid advances in the biological sciences and our ability to address pressing environmental and societal demands.

1.Large mammalian herbivores are well known to shape the structure and function of ecosystems worldwide and these effects can in turn cascade through systems to indirectly influence other animal species. A wealth of studies have explored the effects of large mammals on arthropods, but to date they have reported such widely varying results that generalizations have been elusive. Three factors are likely drivers of this variability: the widely varying life-history characteristics of different arthropod groups, the highly variable landscapes that mammalian herbivores commonly inhabit, and temporal variation in environmental conditions. 2. Here, we use an 18-year-old exclosure experiment stratified across three distinct coastal prairie habitats in northern California to address the effects of a reintroduced mammalian herbivore, tule elk (Cervus canadensis nannodes) on the composition, richness, and abundance of ground-dwelling arthropods over two years with very different precipitation regimes. 3. We found that elk shifted the composition of arthropod communities, increasing the abundance of ants, beetles, spiders and mites, decreasing the abundance of woodlice and bristletails in some but not all habitats types, and having no effect on the abundance of bugs, crickets and springtails. Elk also increased richness and changed the composition of ant-genera and beetle morpho-species. Interestingly, the effects of elk on arthropod composition, richness and abundance varied little between years, despite very different precipitation levels, biomass accumulation, and thatch height. 4. Elk reduced shrub cover, aboveground herbaceous biomass, and thatch height and increased soil compaction, and these changes predicted the abundance and richness of arthropods, although taxonomic groups varied in their responses, presumably due to differences in environmental requirements. 5. Synthesis. Our research highlights the importance of using long-term experiments to assess the cascading effects of large herbivores on the composition of ground-dwelling arthropod communities and to identify the mechanisms that indirectly shape arthropod responses to herbivores among variable habitats and years in order to develop a greater understanding of the variable responses of arthropods to large mammalian herbivores. This article is protected by copyright. All rights reserved.

© 2016, Springer-Verlag Berlin Heidelberg. Understanding the role of biodiversity (B) in maintaining ecosystem function (EF) is a foundational scientific goal with applications for resource management and conservation. Two main hypotheses have emerged that address B–EF relationships: niche complementarity (NC) and the mass-ratio (MR) effect. We tested the relative importance of these hypotheses in a subtropical old-growth forest on the island nation of Taiwan for two EFs: aboveground biomass (ABG) and coarse woody productivity (CWP). Functional dispersion (FDis) of eight plant functional traits was used to evaluate complementarity of resource use. Under the NC hypothesis, EF will be positively correlated with FDis. Under the MR hypothesis, EF will be negatively correlated with FDis and will be significantly influenced by community-weighted mean (CWM) trait values. We used path analysis to assess how these two processes (NC and MR) directly influence EF and may contribute indirectly to EF via their influence on canopy packing (stem density). Our results indicate that decreasing functional diversity and a significant influence of CWM traits were linked to increasing AGB for all eight traits in this forest supporting the MR hypothesis. Interestingly, CWP was primarily influenced by NC and MR indirectly via their influence on canopy packing. Maximum height explained more of the variation in both AGB and CWP than any of the other plant functional traits. Together, our results suggest that multiple mechanisms operate simultaneously to influence EF, and understanding their relative importance will help to elucidate the role of biodiversity in maintaining ecosystem function.

Understanding the consequences of extreme climatic events is a growing challenge in ecology. Climatic extremes may differentially affect varying elements of biodiversity, and may not always produce ecological effects exceeding those of “normal” climatic variation in space and time. We asked how the extreme drought years of 2013–2014 affected the cover, species richness, functional trait means, functional diversity, and phylogenetic diversity of herbaceous plant communities across the California Floristic Province. We compared the directions and magnitudes of these drought effects with expectations from four “pre-drought” studies of variation in water availability: (1) a watering experiment, (2) a long-term (15-yr) monitoring of interannual variability, (3) a resampling of historic (57-yr-old) plots within a warming and drying region, and (4) natural variation in communities over a broad geographic gradient in precipitation. We found that the drought was associated with consistent reductions in species richness and cover, especially for annual forbs and exotic annual grasses, but not with changes in functional or phylogenetic diversity. Except for total cover and cover of exotic annual grasses, most drought effects did not exceed quantitative expectations based on the four pre-drought studies. Qualitatively, plant community responses to the drought were most concordant with responses to pre-drought interannual rainfall variability in the 15-yr monitoring study, and least concordant with responses to the geographic gradient in precipitation. Our results suggest that, at least in the short term, extreme drought may cause only a subset of community metrics to respond in ways that exceed normal background variability.

Journal of Ecology 2016, 104, 1326–1334 doi: 10.1111/1365-2745.12592 Herbivory mediates the long-term shift in the relative importance of microsite and propagule limitation Anu Eskelinen 1,2,3 *, Patrick Saccone 1 , Marko J. Spasojevic 4 and Risto Virtanen 1,2,3 Department of Ecology, University of Oulu, P.O Box 3000, FI-90014 Oulu, Finland; 2 Department of Physiological Diversity, Helmholtz Center for Environmental Research-UFZ, Permoserstr. 15, 04318 Leipzig, Germany; 3 German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, D-04103 Leipzig, Germany; and 4 Institute for Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309, USA Summary 1. Microsite and propagule limitation are predicted to jointly influence plant community assembly and diversity, with shifts in their relative contributions under different ecological conditions. Mam- malian herbivory can also exhibit strong impact on community assembly and diversity. However, to date few studies have considered how herbivory might interact with propagule and microsite limita- tion and how herbivory might alter their relative importance. Even fewer studies have examined how these processes manifest over time to influence community assembly. 2. In fenced and grazed tundra communities that varied in soil moisture, we manipulated propagule limitation by adding seeds of 14 species and manipulated microsite limitation through a one-time disturbance treatment which reduced resident community biomass. We then followed these commu- nities for 11 years to assess the long-term impacts of these processes on community assembly and richness. 3. Herbivory interacted with soil moisture to promote long-term establishment of seeded species: seed addition increased species richness and this effect persisted over 11 years but only in grazed plots, and in drier conditions. Seed addition and herbivory also interacted to drive community com- position. Disturbance initially resulted in greater richness and community divergence, but the effect weakened over time, whereas the effects of herbivory in general strengthened. 4. Synthesis. Our results show that herbivory interacts with environmental conditions to mediate the relative importance of microsite and propagule limitation on community assembly; however, its impacts may only become detectable over longer time-scales. Moreover, our results suggest that her- bivory may be a key biotic modulator of community assembly in low-productivity ecosystems and that incorporating trophic interactions (such as herbivory) into hypotheses about community assem- bly may provide a better understanding of the relative importance of different assembly mecha- nisms. Key-words: assemblage structure and diversity, biotic filtering, determinants of plant community diversity and structure, herbivory, long-term experiment, plant recruitment, seed limitation, species immigration Introduction Recruitment is a key process driving plant community assembly (Grubb 1977; Harper 1977; Tilman & Pacala 1993). Propagule and microsite limitation are two key drivers of plant recruitment and are therefore fundamental to understanding local commu- nity structure and diversity (Eriksson & Ehrl en 1992; Tilman 1997; Zobel et al. 2000; Myers & Harms 2009). Propagule lim- itation occurs when successful recruitment is constrained by *Correspondence author: E-mail: anu.eskelinen@idiv.de limited seed production or dispersal of species in a landscape (Nathan & Muller-Landau 2000; Levine & Murrell 2004). Microsite limitation, on the other hand, occurs when successful recruitment is constrained by the availability of microsites suit- able for germination and establishment, and is jointly influ- enced by both biotic and abiotic environmental factors. For example, microsite limitation can result from competitive sup- pression of immigrants by the resident vegetation or a lack of disturbances that create competition-free safe sites for germina- tion (Stevens et al. 2004; Tilman 2004; Maron et al. 2012), as well as unfavourable soil moisture or nutrient levels (Xiong © 2016 The Authors. Journal of Ecology © 2016 British Ecological Society

In the version of this Perspective originally published, the first author of reference 39 was incorrectly listed as W. Cornwell and the publication year was incorrect. The reference should have read as follows: “Flores-Moreno, H. et al. fungaltraits aka funfun: a dynamic functional trait database for the world's fungi (GitHub, 2019); https://doi.org/10.5281/zenodo.1216257”. This has now been corrected.

The lone star tick, Amblyomma americanum Linnaeus (Ixodida: Ixodidae), is emerging as an important human disease vector in the United States. While some recent studies have modeled broad-scale (regional or county-level) distribution patterns of A. americanum, less is known about how local-scale habitat characteristics drive A. americanum abundance. Such local-scale information is vital to identify targets for tick population control measures within land management units. We investigated how habitat features predict host-seeking A. americanum adult and nymph abundance within a 12-ha oak-hickory forest plot in the Missouri Ozarks. We trapped ticks using CO2-baited traps at 40 evenly spaced locations for three 24-h periods during the summer of 2015, and we measured biotic and abiotic variables surrounding each location. Of 2,008 A. americanum captured, 1,009 were nymphs, and 999 were adults. We observed spatial heterogeneity in local tick abundance (min = 0 ticks, max = 112 ticks, mean = 16.7 ticks per trap night). Using generalized linear mixed models, we found that both nymphs and adults had greater abundance in valleys as well as on northern-facing aspects. Moreover, nymph abundance was negatively related to temperature variance, while adult abundance had a negative relationship with elevation. These results demonstrate that managers in this region may be able to predict local tick abundance through simple physiognomic factors and use these parameters for targeted management action.

Despite decades of research on the species-pool concept and the recent explosion of interest in trait-based frameworks in ecology and biogeography, surprisingly little is known about how spatial and temporal changes in species-pool functional diversity (SPFD) influence biodiversity and the processes underlying community assembly. Current trait-based frameworks focus primarily on community assembly from a static regional species pool, without considering how spatial or temporal variation in SPFD alters the relative importance of deterministic and stochastic assembly processes. Likewise, species-pool concepts primarily focus on how the number of species in the species pool influences local biodiversity. However, species pools with similar richness can vary substantially in functional-trait diversity, which can strongly influence community assembly and biodiversity responses to environmental change. Here, we integrate recent advances in community ecology, trait-based ecology, and biogeography to provide a more comprehensive framework that explicitly considers how variation in SPFD, among regions and within regions through time, influences the relative importance of community assembly processes and patterns of biodiversity. First, we provide a brief overview of the primary ecological and evolutionary processes that create differences in SPFD among regions and within regions through time. We then illustrate how SPFD may influence fundamental processes of local community assembly (dispersal, ecological drift, niche selection). Higher SPFD may increase the relative importance of deterministic community assembly when greater functional diversity in the species pool increases niche selection across environmental gradients. In contrast, lower SPFD may increase the relative importance of stochastic community assembly when high functional redundancy in the species pool increases the influence of dispersal history or ecological drift. Next, we outline experimental and observational approaches for testing the influence of SPFD on assembly processes and biodiversity. Finally, we highlight applications of this framework for restoration and conservation. This species-pool functional diversity framework has the potential to advance our understanding of how local- and regional-scale processes jointly influence patterns of biodiversity across biogeographic regions, changes in biodiversity within regions over time, and restoration outcomes and conservation efforts in ecosystems altered by environmental change.

Author(s): Wang, X; Wiegand, T; Anderson-Teixeira, KJ; Bourg, NA; Hao, Z; Howe, R; Jin, G; Orwig, DA; Spasojevic, MJ; Wang, S; Wolf, A; Myers, JA | Abstract: Aims: Patterns of spatial community dissimilarity have inspired a large body of theory in ecology and biogeography. Yet key gaps remain in our understanding of the local-scale ecological processes underlying species replacement and species nestedness, the two fundamental components of spatial community dissimilarity. Here, we examined the relative influence of dispersal limitation, habitat filtering and interspecific species interactions on local-scale patterns of the replacement and nestedness components in eight stem-mapped temperate forest mega-plots at different ontogenetic stages (large versus small trees). Location: Eight large (20–35 ha), fully mapped temperate forest plots in northern China and northern U.S.A. Time period: 2004–2016. Major taxa studied: Woody plants. Methods: We combined decomposition of community dissimilarity (based on the Ružicka index) and spatial point-pattern analysis to compare the spatial (i.e., distance-dependent) replacement and nestedness components of each plot with that expected under five spatiallynexplicit null models representing different hypotheses on community-assembly mechanisms. Results: Our analyses revealed complex results. In all eight forests, spatial community dissimilarity was best explained by species replacement among local tree assemblages and by a null model based on dispersal limitation. In contrast, spatial nestedness for large and small trees was best explained by random placement and habitat filtering, respectively, in addition to dispersal limitation. However, interspecific interactions did not contribute to local replacement and nestedness. Main conclusions: Species replacement is the predominant process accounting for spatial community dissimilarity in these temperate forests and caused largely by local-scale species clustering associated with dispersal limitation. Nestedness, in contrast, is less prevalent and primarily associated with larger variation in local species richness as caused by spatial richness gradients or ‘hotspots’ of local species richness. The novel use of replacement and nestedness measures in point pattern analysis is a promising approach to assess local-scale biodiversity patterns and to explore their causes.

© 2018 by the Ecological Society of America Extreme droughts such as the one that affected California in 2012–2015 have been linked to severe ecological consequences in perennial-dominated communities such as forests. In annual communities, drought impacts are difficult to assess because many species persist through facultative multiyear seed dormancy, which leads to the development of seed banks. Impacts of extreme drought on the abundance and composition of the seed banks of whole communities are little known. In 80 heterogeneous grassland plots where cover is dominated by ~15 species of exotic annual grasses and diversity is dominated by ~70 species of native annual forbs, we grew out seeds from soil cores collected early in the California drought (2012) and later in the multiyear drought (2014), and analyzed drought-associated changes in the seed bank. Over the course of the study we identified more than 22,000 seedlings to species. We found that seeds of exotic annual grasses declined sharply in abundance during the drought while seeds of native annual forbs increased, a pattern that resembled but was even stronger than the changes in aboveground cover of these groups. Consistent with the expectation that low specific leaf area (SLA) is an indicator of drought tolerance, we found that the community-weighted mean SLA of annual forbs declined both in the seed bank and in the aboveground community, as low-SLA forbs increased disproportionately. In this system, seed dormancy reinforces the indirect benefits of extreme drought to the native forb community.

Altres ajuts europeus: P.A.W. was additionally supported by the European Union Fourth Environment and Climate Framework Programme (Project Number ENV4-CT970586)P.A.W. was additionally supported by the European Union Fourth Environment and Climate Framework Programme (Project Number ENV4-CT970586). The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; 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

Our ability to understand and predict the response of ecosystems to a changing environment depends on quantifying vegetation functional diversity. However, representing this diversity at the global scale is challenging. Typically, in Earth system models, characterization of plant diversity has been limited to grouping related species into plant functional types (PFTs), with all trait variation in a PFT collapsed into a single mean value that is applied globally. Using the largest global plant trait database and state of the art Bayesian modeling, we created fine-grained global maps of plant trait distributions that can be applied to Earth system models. Focusing on a set of plant traits closely coupled to photosynthesis and foliar respiration—specific leaf area (SLA) and dry mass-based concentrations of leaf nitrogen (Nm) and phosphorus (Pm), we characterize how traits vary within and among over 50,000 ∼50×50-km cells across the entire vegetated land surface. We do this in several ways—without defining the PFT of each grid cell and using 4 or 14 PFTs; each model’s predictions are evaluated against out-of-sample data. This endeavor advances prior trait mapping by generating global maps that preserve variability across scales by using modern Bayesian spatial statistical modeling in combination with a database over three times larger than that in previous analyses. Our maps reveal that the most diverse grid cells possess trait variability close to the range of global PFT means., This research was supported as part of the Energy Exascale Earth System Model (E3SM) project, funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research (Grant DE-SC0012677 to P.B.R. and A.B.). O.K.A. acknowledges the support of the Australian Research Council (CE140100008). This research was also funded by programs from the NSF Long-Term Ecological Research (Grant DEB-1234162) and Long-Term Research in Environmental Biology (Grant DEB-1242531). A.B., F.F., and P.B.R. acknowledge funding from NSF Grant IIS-1563950. P.B.R. also acknowledges support from two University of Minnesota Institute on the Environment discovery grants. This study has been supported by the TRY initiative on plant traits (www.try-db.org). The TRY database is hosted at the Max Planck Institute for Biogeochemistry (Jena, Germany) and supported by DIVERSITAS/Future Earth, the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, and the EU H2020 project BACI (Grant 640176). B.B. acknowledges a Natural Environment Research Council (NERC) independent research fellowship NE/M019160/1. J.P. acknowledges the financial support from the European Research Council Synergy Grant ERC-SyG-2013-610028 IMBALANCE-P, the Spanish Government Grant CGL2013-48074-P, and the Catalan Government Grant SGR 2014-274. B.B.-L. was supported by the Earth System Modeling program of the US Department of Energy, Office of Science, Office of Biological and Environmental Research. K.K. acknowledges the contribution of the Wageningen University and Research Investment theme Resilience for the project Resilient Forest (KB-29-009-003). P.M. acknowledges support from ARC Grant FT110100457 and NERC Grant NE/F002149/1. W.H. acknowledges support from the National Natural Science Foundation of China (Grant 41473068) and the “Light of West China” Program of the Chinese Academy of Sciences.

One primary goal at the intersection of community ecology and global change biology is to identify functional traits that are useful for predicting plant community response to global change. We used observations of community composition from a long‐term field experiment in two adjacent plant communities (grassland and coastal sage shrub) to investigate how nine key plant functional traits were related to altered water and nitrogen availability following fire. We asked whether the functional responses of species found in more than one community type were context dependent and whether community‐weighted mean and functional diversity were significantly altered by water and nitrogen input. Our results suggest varying degrees of context dependency. We found that plants with high leaf nitrogen concentration (specifically nitrogen fixers), shallow roots, and low leaf mass per unit area and plant‐level transpiration were similarly negatively influenced by added nitrogen across community types. In contrast, responses to water manipulations exhibited greater context dependency; plants with high water‐use efficiency, lower plant‐level transpiration rates, and shallower roots were negatively impacted by simulated drought in the shrub‐dominated community, but there was no significant relationship between these traits and changes in water inputs in the grassland community. Similarly, we found context dependency in community‐wide trait responses to global change. Functional diversity tended to be higher in plots with reduced water as compared to those with added water in grassland, while the opposite trend was observed in coastal sage scrub. Our results indicate that some traits are strong predictors of species and community response to altered water and nitrogen availability, but the magnitude and direction of the response may be modulated by the abiotic and biotic context.

Questions Are patterns of intra- and inter-specific functional trait variation consistent with greater abiotic filtering on community assembly at high latitudes and elevations, and greater biotic filtering at low latitudes and elevations? Locations Area de Conservacion Guanacaste, Costa Rica; Santa Catalina Mountains, Arizona; Siskiyou Mountains, Oregon. Methods We measured woody plant species abundance and a key functional trait associated with competition for resources and environmental tolerance (specific leaf area, SLA) along elevational gradients in low-latitude tropical (Costa Rica), mid-latitude desert (Arizona) and high latitude mediterranean (southern Oregon) biomes. We explored patterns of abiotic and biotic filtering by comparing observed patterns of community-weighted means and variances along elevational and latitudinal gradients to those expected under random assembly. In addition, we related trait variability to niches and explored how total trait space and breadth vary across broad spatial gradients by quantifying the ratio of intra- to inter-specific variation. Results Both the community-wide mean and variance of SLA decreased with increasing latitude, consistent with greater abiotic filtering at higher latitudes. Further, low-elevation communities had higher trait variation than expected by chance, consistent with greater biotic filtering at low elevations. Finally, in the tropics and across latitude the ratio of intra- to inter-specific variation was negatively correlated to species richness, which further suggests that biotic interactions influence plant assembly at low latitudes. Conclusions Intra- and inter-specific patterns of SLA variation appeared broadly consistent with the idea that the relative strength of biotic and abiotic drivers on community assembly changes along elevational and latitudinal gradients; evidence for biotic drivers appeared more prominent at low latitudes and elevations and evidence for abiotic drivers appeared more prominent at high latitudes and elevations.

Journal of Ecology 2016, 104, 487–496 doi: 10.1111/1365-2745.12518 When does intraspecific trait variation contribute to functional beta-diversity? Marko J. Spasojevic 1 *, Benjamin L. Turner 2 and Jonathan A. Myers 1 Department of Biology and Tyson Research Center, Washington University in St. Louis, St. Louis, MO 63130, USA; and 2 Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Panama Summary 1. Intraspecific trait variation (ITV) is hypothesized to play an important role in community assem- bly and the maintenance of biodiversity. However, fundamental gaps remain in our understanding of how ITV contributes to mechanisms that create spatial variation in the functional-trait composition of communities (functional b-diversity). Importantly, ITV may influence the perceived importance of environmental filtering across spatial scales. 2. We examined how ITV contributes to functional b-diversity and environmental filtering in woody plant communities in a temperate forest in the Ozark ecoregion, Missouri, USA. To test the hypothe- sis that ITV contributes to changes in the perceived importance of environmental filtering across scales, we compared patterns of functional b-diversity across soil-resource and topographic gradients at three spatial grains and three spatial extents. To quantify the contribution of ITV to functional b-diversity, we compared patterns that included ITV in five traits (leaf area, specific leaf area, leaf water content, leaf toughness and chlorophyll content) to patterns based on species-mean trait values. 3. Functional b-diversity that included ITV increased with spatial extent and decreased with spatial grain, suggesting stronger environmental filtering within spatially extensive landscapes that contain populations locally adapted to different habitats. In contrast, functional b-diversity based on species- mean trait values increased with spatial extent but did not change with spatial grain, suggesting weaker environmental filtering among larger communities which each contain a variety of habitats and locally adapted populations. 4. Synthesis. Although studies typically infer community assembly mechanisms from species-mean trait values, our study suggests that mean trait values may mask the strength of assembly mecha- nisms such as environmental filtering, especially in landscape-scale studies that encompass strong environmental gradients and locally adapted populations. Our study highlights the utility of integrat- ing ITV into studies of functional b-diversity to better understand the ecological conditions under which trait variation within and among species contributes most strongly to patterns of biodiversity across spatial scales. Key-words: community assembly, determinants of plant community diversity and structure, envi- ronmental filtering, functional diversity, Ozark oak-hickory forest, plant functional traits, spatial scale, species sorting, Tyson Research Center Plot Introduction Community assembly represents the outcome of multiple pro- cesses operating over multiple scales (Diamond 1975; Vellend 2010; Weiher et al. 2011; HilleRisLambers et al. 2012). To better understand the interplay of processes across scales, ecologists often examine patterns and causes of variation in community composition, known as b-diversity, a metric that *Correspondence author: E-mail: mspaso@gmail.com links local (a) and regional (c) patterns of biodiversity (Whit- taker, Willis & Field 2001; Anderson et al. 2011). Recently, there has been a surge of interest in quantifying trait variation among communities (functional b-diversity) to infer the rela- tive importance of dispersal, ecological drift and niche selec- tion as drivers of community assembly (e.g., Swenson, Anglada-Cordero & Barone 2011; Siefert et al. 2013; Spaso- jevic, Copeland & Suding 2014). Concurrently, a growing number of theoretical and observational studies suggest that conceptual frameworks in trait-based community ecology © 2015 The Authors. Journal of Ecology © 2015 British Ecological Society

Temperature is increasing at unprecedented rates across most of the tundra biome. Remote-sensing data indicate that contemporary climate warming has already resulted in increased productivity over much of the Arctic, but plot-based evidence for vegetation transformation is not widespread. We analysed change in tundra vegetation surveyed between 1980 and 2010 in 158 plant communities spread across 46 locations. We found biome-wide trends of increased height of the plant canopy and maximum observed plant height for most vascular growth forms; increased abundance of litter; increased abundance of evergreen, low-growing and tall shrubs; and decreased abundance of bare ground. Intersite comparisons indicated an association between the degree of summer warming and change in vascular plant abundance, with shrubs, forbs and rushes increasing with warming. However, the association was dependent on the climate zone, the moisture regime and the presence of permafrost. Our data provide plot-scale evidence linking changes in vascular plant abundance to local summer warming in widely dispersed tundra locations across the globe. © 2012 Macmillan Publishers Limited. All rights reserved.

Modified environmental conditions are driving phenological changes in ecosystems around the world. Many plants have already responded to warmer temperatures by flowering earlier and sustaining longer periods of growth. Changes in other environmental factors, like precipitation and atmospheric nitrogen (N) deposition, may also influence phenology but have been less studied. Alpine plants may be good predictors of phenological response patterns because environmental changes are amplified in mountain ecosystems and extreme conditions may make alpine plants particularly sensitive to changes in limiting factors like precipitation, temperature, and N. We tested the effects of increased snowpack, temperature, and N on alpine tundra plant phenology, using snow fence, open-top warming chamber, and N fertilization treatments at the Niwot Ridge Long Term Ecological Research (LTER) site. Flowering phenology of three abundant species was recorded during two growing seasons. Treatment responses varied among sp...

Summary 1. Many studies of community assembly focus on two mechanisms: environmental filtering and competitive interactions. This focus ignores the importance of other assembly processes such as equalizing fitness processes and facilitation. The contribution of different processes to community assembly can be elucidated by examining functional diversity patterns of traits that differ in their contribution to different assembly processes. 2. In alpine tundra, we explored trait patterns along a stress–resource gradient that varied in productivity, nitrogen availability and soil moisture. We explore whether functional diversity is low in abiotic stressful environments and increases in more benign environments as competition becomes more important, and if equalizing fitness processes and facilitation affect functional diversity. We calculated community-weighted mean trait values and functional diversity for specific leaf area (SLA), leaf area, stomatal conductance, plant height and chlorophyll content as well as multivariate functional diversity and phylogenetic diversity. 3. At the community level, functional diversity increased at both ends of the gradient: high resource availability was associated with greater functional diversity in height and leaf area, and lower resource availability was associated with greater functional diversity in SLA, stomatal conductance, and chlorophyll content. As a result of this trade-off in functional diversity among traits, multivariate functional diversity did not change across the gradient. Phylogenetic diversity increased with increasing resource availability. 4. We find evidence for at least three assembly processes along the gradient. Abiotic filtering by wind and cold exposure may reduce functional diversity in height and leaf area at the low resource end of the gradient. Also at low resource availability, increasing functional diversity in the other three traits suggests competition for below-ground resources. At the resource-rich end of the gradient, increased functional diversity in height and leaf area suggests increased competition for light or facilitation. 5.Synthesis: Our results suggest that multiple assembly processes (abiotic filtering, above-ground competition, and below-ground competition) operate simultaneously to structure plant communities along a stress–resource gradient. These processes would be obscured by a single multivariate trait index or phylogenetic diversity and are only evident by analysing functional diversity patterns of individual traits.