Community Functional Responses to Soil and Climate at Multiple Spatial Scales: When Does Intraspecific Variation Matter?

Despite increasing evidence of the importance of intraspecific trait variation in plant communities, its role in community trait responses to environmental variation, particularly along broad-scale climatic gradients, is poorly understood. We analyzed functional trait variation among early-successional herbaceous plant communities (old fields) across a 1200-km latitudinal extent in eastern North America, focusing on four traits: vegetative height, leaf area, specific leaf area (SLA), and leaf dry matter content (LDMC). We determined the contributions of species turnover and intraspecific variation to between-site functional dissimilarity at multiple spatial scales and community trait responses to edaphic and climatic factors. Among-site variation in community mean trait values and community trait responses to the environment were generated by a combination of species turnover and intraspecific variation, with species turnover making a greater contribution for all traits. The relative importance of intraspecific variation decreased with increasing geographic and environmental distance between sites for SLA and leaf area. Intraspecific variation was most important for responses of vegetative height and responses to edaphic compared to climatic factors. Individual species displayed strong trait responses to environmental factors in many cases, but these responses were highly variable among species and did not usually scale up to the community level. These findings provide new insights into the role of intraspecific trait variation in plant communities and the factors controlling its relative importance. The contribution of intraspecific variation to community trait responses was greatest at fine spatial scales and along edaphic gradients, while species turnover dominated at broad spatial scales and along climatic gradients.     

Using functional trait diversity to evaluate the contribution of multiple ecological processes to community assembly during succession

Successional chronosequences provide a unique opportunity to study the effects of multiple ecological processes on plant community assembly. Using a series of 0.5 × 0.5 m² plots (n = 30) from five successional sub‐alpine meadow plant communities (ages 3, 5, 9, 12, and undisturbed) in the Qinghai‐Tibetan Plateau, we investigated whether community assembly is stochastic or deterministic for species and functional traits. We tested directional change in species composition, functional trait composition, and then functional trait diversity measured by Rao's quadratic entropy for four traits – plant height, leaf dry matter content, specific leaf area, and seed mass – along two comparable successional chronosequences. We then evaluated the importance of species interactions, habitat filtering and stochasticity by comparing with random communities and partitioning the environmental and spatial components of Rao's quadratic entropy. We found no directional change in species composition, but clear directionality in functional trait composition. None of the abiotic environmental variables (except P) showed linear change with successional age, but soil moisture and nitrogen were positively related to functional diversity within meadows. Functional trait diversity increased significantly with the increase in successional age. Comparison with random communities showed a significant shift from trait divergence in early stages of succession (3‐ and 5‐yr) to convergence in the later stages of succession 9‐, 12‐yr and undisturbed). The relative importance of abiotic variables and spatial structure for functional trait diversity changed in a predictable manner with successional age. Stochasticity at the species level may indicate dispersal limitation, but deterministic effects on functional trait distributions show the role of both habitat effects and biotic interactions.     

Environmental associations of abundance-weighted functional traits in Australian plant communities

Predictions of how vegetation responds to spatial and temporal differences in climate rely on established links with plant functional traits and vegetation types that can be encoded into Dynamic Global Vegetation Models. Individual traits have been linked to climate at species level and at community level within regions. However, a recent global assessment of aggregated community level traits found unexpectedly weak links with macroclimate, bringing into question broadscale trait–climate associations and implicating local-scale environmental differences in the filtering of communities. To further evaluate patterns in light of these somewhat contradictory results, we quantified the power of macro-environmental variables to explain aggregated plant community traits, taking advantage of new trait data for leaf area, plant height and seed mass combined with a national survey that records cover-abundance using consistent methods for a large number of plots across Australia. In contrast to the global study, we found that abundance-weighted community mean and variance of leaf area and maximum height were correlated with macroclimate. Height and leaf area were highest in wet (especially warm, wet) environments, with actual evapotranspiration explaining 30% of variation in leaf area and 26% in maximum height. Seed mass was weakly related to environment, with no variable explaining more than 5% of variance. Considering all three traits together in a redundancy analysis, the complete set of environmental variables explained 43% of variation in site-mean traits and 29% of within-site trait variance. While significant trait variation remains unexplained, the trait–environment relationships reported here suggest climatically-driven filtering plays a strong role in assembling these vegetation communities. Regional assessments using standardised species abundances can therefore be used to predict aspects of vegetation function. Our quantification of plant community trait patterns along macroclimatic gradients at continental scale thereby contributes a much-needed functional basis for Australian vegetation.     

A functional trait-based approach to understand community assembly and diversity–productivity relationships over 7 years in experimental grasslands

Several multi-year biodiversity experiments have shown positive species richness–productivity relationships which strengthen over time, but the mechanisms which control productivity are not well understood. We used experimental grasslands (Jena Experiment) with mixtures containing different numbers of species (4, 8, 16 and 60) and plant functional groups (1–4; grasses, legumes, small herbs, tall herbs) to explore patterns of variation in functional trait composition as well as climatic variables as predictors for community biomass production across several years (from 2003 to 2009). Over this time span, high community mean trait values shifted from the dominance of trait values associated with fast growth to trait values suggesting a conservation of growth-related resources and successful reproduction. Increasing between-community convergence in means of several productivity-related traits indicated that environmental filtering and exclusion of competitively weaker species played a role during community assembly. A general trend for increasing functional trait diversity within and convergence among communities suggested niche differentiation through limiting similarity in the longer term and that similar mechanisms operated in communities sown with different diversity. Community biomass production was primarily explained by a few key mean traits (tall growth, large seed mass and leaf nitrogen concentration) and to a smaller extent by functional diversity in nitrogen acquisition strategies, functional richness in multiple traits and functional evenness in light-acquisition traits. Increasing species richness, presence of an exceptionally productive legume species (Onobrychis viciifolia) and climatic variables explained an additional proportion of variation in community biomass. In general, community biomass production decreased through time, but communities with higher functional richness in multiple traits had high productivities over several years. Our results suggest that assembly processes within communities with an artificially maintained species composition maximize functional diversity through niche differentiation and exclusion of weaker competitors, thereby maintaining their potential for high productivity.     

Functional traits composition predict macrophytes community productivity along a water depth gradient in a freshwater lake

Functional trait composition of plant communities has been proposed as a helpful key for understanding the mechanisms of biodiversity effects on ecosystem functioning. In this study, we applied a step‐wise modeling procedure to test the relative effects of taxonomic diversity, functional identity, and functional diversity on macrophytes community productivity along water depth gradient. We sampled 42 plots and 1513 individual plants and measured 16 functional traits and abundance of 17 macrophyte species. Results showed that there was a significant decrease in taxonomic diversity, functional identity (i.e., stem dry mass content, leaf [C] and leaf [N]), and functional diversity (i.e., floating leaf, mean Julian flowering date and rooting depth) with increasing water depth. For the multiple‐trait functional diversity (FD) indices, functional richness decreased, while functional divergence increased with water depth gradient. Macrophyte community productivity was strongly determined by functional trait composition within community, but not significantly affected by taxonomic diversity. Community‐weighted means (CWM) showed a two times higher explanatory power relative to FD indices in determining variations in community productivity. For nine of sixteen traits, CWM and FD showed significant correlations with community productivity, although the strength and direction of those relations depended on selected trait. Furthermore, functional composition in a community affected productivity through either additive or opposite effects of CWM and FD, depending on the particular traits being considered. Our results suggested both mechanisms of mass ratio and niche complementarity can operate simultaneously on variations in community productivity, and considering both CWM and FD would lead to a more profound understanding of traits–productivity relationships.     

Differential effects of functional traits on aboveground biomass in semi-natural grasslands

Despite increasing evidence on the importance of species functional characteristics for ecosystem processes, two major hypotheses suggest different mechanisms: the ‘mass ratio hypothesis’ assumes that functional traits of the dominant species determine ecosystem processes, while the ‘complementarity hypothesis’ predicts that resource niches may be used more completely when a community is functionally more diverse. Here, we present a method which uses two different groups of biotic predictor variables being (1) abundance‐weighted mean (=aggregated) trait values and (2) functional trait diversity based on Rao's quadratic diversity (FD_Q) to test the competing hypotheses on biodiversity–ecosystem functioning relationships after accounting for co‐varying abiotic factors. We applied this method to data recorded on biodiversity–biomass relationships and environmental variables in 35 semi‐natural temperate grasslands and used a literature‐based matrix of fourteen plant functional traits to assess the explanatory power of models including different sets of predictor variables. Aboveground community biomass did not correlate with species richness. Abiotic factors, in particular soil nitrogen concentration, explained about 50% of variability in aboveground biomass. The best model incorporating functional trait diversity explained only about 30%, while the best model based on aggregated trait values explained about 54% of variability in aboveground biomass. The inclusion of all predictor variable groups in a combined model increased the predictive power to about 75%. This model comprised soil nitrogen concentration as abiotic factor, aggregated traits being indicative for species competitive dominance (rooting depth, leaf distribution, specific leaf area, perennial life cycle) and functional trait diversity in vegetative plant height, leaf area and life cycle. Our study strongly suggests that abiotic factors, trait values of the dominant species and functional trait diversity in combination may best explain differences in aboveground community biomass in natural ecosystems and that their isolated consideration may be misleading.     

外来物种刺槐对黄土丘陵区植物群落功能结构的影响

在黄土丘陵区草原带、森林草原带和森林带3个植被带选取成对的刺槐群落和乡土植物群落功能性状值,研究不同植被带刺槐群落、乡土植物群落功能结构的变化,以及同一植被带下刺槐的引入对群落功能结构的影响.结果表明: 刺槐群落和乡土植物群落的叶碳、叶氮、叶磷、比叶面积、叶组织密度等功能性状随植被带的变化规律一致.刺槐群落叶碳、叶氮、比叶面积显著高于乡土植物群落,且2种群落功能多样性指数(FR_ic、FE_ve、FD_iv、FD_is、Rao)随植被带的变化趋势并不完全一致,在森林带刺槐的引入提高了植物群落功能多样性,在草原带降低了植物群落功能多样性.     

Shifts in plant functional community composition under hydrological stress strongly decelerate litter decomposition

Litter decomposition is a key process of nutrient and carbon cycling in terrestrial ecosystems. The decomposition process will likely be altered under ongoing climate change, both through direct effects on decomposer activity and through indirect effects caused by changes in litter quality. We studied how hydrological change indirectly affects decomposition via plant functional community restructuring caused by changes in plant species’ relative abundances (community‐weighted mean (CWM) traits and functional diversity). We further assessed how those indirect litter quality effects compare to direct effects. We set up a mesocosm experiment, in which sown grassland communities and natural turf pieces were subjected to different hydrological conditions (dryness and waterlogging) for two growing seasons. Species‐level mean traits were obtained from trait databases and combined with species’ relative abundances to assess functional community restructuring. We studied decomposition of mixed litter from these communities in a common “litterbed.” These indirect effects were compared to effects of different hydrological conditions on soil respiration and on decomposition of standard litter (direct effects). Dryness reduced biomass production in sown communities and natural turf pieces, while waterlogging only reduced biomass in sown communities. Hydrological stress caused profound shifts in species’ abundances and consequently in plant functional community composition. Hydrologically stressed communities had higher CMW leaf dry matter content, lower CMW leaf nitrogen content, and lower functional diversity. Lower CWM leaf N content and functional diversity were strongly related to slower decomposition. These indirect effects paralleled direct effects, but were larger and longer‐lasting. Species mean traits from trait databases had therefore considerable predictive power for decomposition. Our results show that stressful soil moisture conditions, that are likely to occur more frequently in the future, quickly shift species’ abundances. The resulting functional community restructuring will decelerate decomposition under hydrological stress.     

Trait‐mediated community assembly: distinguishing the signatures of biotic and abiotic filters

Conflicting hypotheses predict how traits mediate species establishment and community assembly. Traits of newly establishing individuals are predicted to converge, or be more similar to the resident, preexisting community, when the biotic or abiotic environment favors a single best phenotype, but are predicted to diverge when trait differences reduce competitive interactions. We tested these competing hypotheses using transplant seedlings in an old‐field environment, and assessed the contribution of inter‐ and intra‐specific transplant trait variation to community‐level patterns. Using a soil moisture gradient and resident plant removals, we determined when traits of newly‐establishing plants converge or diverge from the resident community by calculating community weighted mean traits for transplant and resident communities. We saw evidence of environmentally‐ and competitively‐driven trait shifts that resulted in both trait convergence and divergence from the resident community, whose traits reflect the combined effects of both drivers. Leaf dry matter content (LDMC) of transplants diverged in the presence of competition, whereas plant height and stem‐specific density (SSD) showed the opposite pattern, converging with the resident community in their presence. Specific leaf area (SLA) shifted with competition but did not reflect resident community SLA. All transplant traits were influenced by soil moisture, often in an interaction with competition, indicating that the strength of convergence or divergence is contingent on the abiotic environment. Intraspecific differences in transplant traits among treatments were evident in three of four traits; intraspecific height and SLA trends mirrored transplant community‐level trends, whereas intraspecific shifts in SSD were distinct from community‐level trends. Our study shows competition between plant species may cause traits of newly establishing plants to converge with the resident community, as frequently as it selects for trait divergence. These opposing effects of competition suggest that it plays a pervasive role in both intraspecific and species‐level trait differences among communities.     

Plant functional traits capture species richness variations along a flooding gradient

Local species coexistence is the outcome of abiotic and biotic filtering processes which sort species according to their trait values. However, the capacity of trait‐based approaches to predict the variation in realized species richness remains to be investigated. In this study, we asked whether a limited number of plant functional traits, related to the leaf‐height‐seed strategy scheme and averaged at the community level, is able to predict the variation in species richness over a flooding disturbance gradient. We further investigated how these mean community traits are able to quantify the strength of abiotic and biotic processes involved in the disturbance–productivity–diversity relationship. We thus tested the proposal that the deviation between the fundamental species richness, assessed from ecological niche‐based models, and realized species richness, i.e. field‐observed richness, is controlled by species interactions. Flooding regime was determined using a detailed hydrological model. A precise vegetation sampling was performed across 222 quadrats located throughout the flooding gradient. Three core functional traits were considered: specific leaf area (SLA), plant height and seed mass. Species richness showed a hump‐shaped response to disturbance and productivity, but was better predicted by only two mean community traits: SLA and height. On the one hand, community SLA that increased with flooding, controlled the disturbance‐diversity relationship through habitat filtering. On the other hand, species interactions, the strength of which was captured by community height values, played a strong consistent role throughout the disturbance gradient by reducing the local species richness. Our study highlights that a limited number of simple, quantitative, easily measurable functional traits can capture the variation in plant species richness at a local scale and provides a promising quantification of key community assembly mechanisms.     

Partitioning of functional diversity reveals the scale and extent of trait convergence and divergence

Questions: Trait differentiation among species occurs at different spatial scales within a region. How does the partitioning of functional diversity help to identify different community assembly mechanisms? Location: Northeastern Spain. Methods: Functional diversity can be partitioned into within‐community (α) and among‐communities (β) components, in analogy to Whittaker's classical α and β species diversity concept. In light of ecological null models, we test and discuss two algorithms as a framework to measure α and β functional diversity (the Rao quadratic entropy index and the variance of trait values). Species and trait (specific leaf area) data from pastures under different climatic conditions in NE Spain are used as a case study. Results: The proposed indices show different mathematical properties but similarly account for the spatial components of functional diversity. For all vegetation types along the climatic gradient, the observed α functional diversity was lower than expected at random, an observation consistent with the hypothesis of trait convergence resulting from habitat filtering. On the other hand, our data exhibited a remarkably higher functional diversity within communities compared to among communities (α?β). In contrast to the high species turnover, there was a limited functional diversity turnover among communities, and a large part of the trait divergence occurred among coexisting species. Conclusions: Partitioning functional diversity within and among communities revealed that both trait convergence and divergence occur in the formation of assemblages from the local species pool. A considerable trait convergence exists at the regional scale in spite of changes in species composition, suggesting the existence of ecological redundancy among communities.     

Filling the gap in functional trait databases: use of ecological hypotheses to replace missing data

Functional trait databases are powerful tools in ecology, though most of them contain large amounts of missing values. The goal of this study was to test the effect of imputation methods on the evaluation of trait values at species level and on the subsequent calculation of functional diversity indices at community level using functional trait databases. Two simple imputation methods (average and median), two methods based on ecological hypotheses, and one multiple imputation method were tested using a large plant trait database, together with the influence of the percentage of missing data and differences between functional traits. At community level, the complete‐case approach and three functional diversity indices calculated from grassland plant communities were included. At the species level, one of the methods based on ecological hypothesis was for all traits more accurate than imputation with average or median values, but the multiple imputation method was superior for most of the traits. The method based on functional proximity between species was the best method for traits with an unbalanced distribution, while the method based on the existence of relationships between traits was the best for traits with a balanced distribution. The ranking of the grassland communities for their functional diversity indices was not robust with the complete‐case approach, even for low percentages of missing data. With the imputation methods based on ecological hypotheses, functional diversity indices could be computed with a maximum of 30% of missing data, without affecting the ranking between grassland communities. The multiple imputation method performed well, but not better than single imputation based on ecological hypothesis and adapted to the distribution of the trait values for the functional identity and range of the communities. Ecological studies using functional trait databases have to deal with missing data using imputation methods corresponding to their specific needs and making the most out of the information available in the databases. Within this framework, this study indicates the possibilities and limits of single imputation methods based on ecological hypothesis and concludes that they could be useful when studying the ranking of communities for their functional diversity indices.     

Leaf trait integration mediates species richness variation in a species-rich neotropical forest domain

Environmental gradients are known to drive changes in mean trait values, but changes in the trait integration strength across local communities are less well understood, particularly with regard to possible links with species richness variation. Here, we tested if climate, soil, and topography gradients drive species richness indirectly via constraints on trait integration in the Atlantic Forest of South America. We evaluated seven traits (from leaf, wood, seed, and plant size) of 1456 species occurring across 84 local communities. Generalized least square models and a path model were applied to test direct and indirect relationships. Correlations were higher between leaf traits (average r?=?0.28) and lower when other traits were included (average r?=?0.16). In line with this result, species richness was related to a multivariate index of interspecific trait integration (ITI) computed for leaf traits, but not to the ITI for all the seven traits. Abiotic gradients influenced species richness both directly and indirectly through the leaf trait integration. A total of 33% and 26% of the variation in species richness and ITI, respectively, were explained by the models, with climatic conditions showing higher contribution than topographic and edaphic factors. These results support a significant but reduced environmental selection role behind the trait-based community assembly and may suggest that other processes are involved in the constrain of trait integration at larger spatial scales. In addition, different directional trends in trait–trait relationships across local communities suggest that global trait relationships may not necessarily hold at local contexts.

     

中国东部海岛黑松群落功能多样性的纬度变异及其影响因素

黑松(Pinus thunbergii)群落在中国东海和黄海海域的海岛广泛分布, 研究其功能多样性的纬度变化特征及其影响因素, 有助于揭示是否在高度隔离的片断化景观中, 同一植物群落类型的生物多样性也具有显著的纬度地带性特征。该研究调查和测定了中国东部海域跨越13个纬度的27个海岛60个黑松群落的物种组成和植物功能性状, 分析了生物因素(黑松优势度和物种多样性)与非生物因素(年平均气温、总太阳辐射和干旱指数)与黑松群落功能多样性的关系, 并利用广义线性回归和方差分解揭示了各影响因素对黑松群落功能多样性的相对影响。主要结果: 随纬度升高, 群落的黑松优势度和物种丰富度, 以及枝干性状和枝叶性状总体的功能丰富度、功能分散度、Rao二次熵均显著降低, 但叶片功能多样性无显著变化趋势。黑松优势度、物种多样性和气候综合解释了枝叶性状总体功能丰富度、分散度和Rao二次熵变异的63%、47%和39%, 枝干性状功能丰富度、分散度和Rao二次熵变异的56%、67%和53%, 对叶片性状功能多样性的综合解释度较低(21%-30%)。物种丰富度和辛普森多样性显著增加叶功能多样性, 香农-维纳多样性显著降低叶功能丰富度。干旱度显著增加枝叶性状总体和枝干功能多样性, 年平均气温显著降低枝干功能分散度和Rao二次熵。该结果表明, 中国东部海岛黑松群落的功能多样性具有明显的纬度格局, 气候因素和物种丰富度是决定黑松群落功能多样性纬度变异的重要因素。     

Processes of community assembly in an environmentally heterogeneous,high biodiversity region

Despite decades of study, the relative importance of niche‐based versus neutral processes in community assembly remains largely ambiguous. Recent work suggests niche‐based processes are more easily detectable at coarser spatial scales, while neutrality dominates at finer scales. Analyses of functional traits with multi‐year multi‐site biodiversity inventories may provide deeper insights into assembly processes and the effects of spatial scale. We examined associations between community composition, species functional traits, and environmental conditions for plant communities in the Kouga‐Baviaanskloof region, an area within South Africa's Cape Floristic Region (CFR) containing high α and β diversity. This region contains strong climatic gradients and topographic heterogeneity, and is comprised of distinct vegetation classes with varying fire histories, making it an ideal location to assess the role of niche‐based environmental filtering on community composition by examining how traits vary with environment. We combined functional trait measurements for over 300 species with observations from vegetation surveys carried out in 1991/1992 and repeated in 2011/2012. We applied redundancy analysis, quantile regression, and null model tests to examine trends in species turnover and functional traits along environmental gradients in space and through time. Functional trait values were weakly associated with most spatial environmental gradients and only showed trends with respect to vegetation class and time since fire. However, survey plots showed greater compositional and functional stability through time than expected based on null models. Taken together, we found clear evidence for functional distinctions between vegetation classes, suggesting strong environmental filtering at this scale, most likely driven by fire dynamics. In contrast, there was little evidence of filtering effects along environmental gradients within vegetation classes, suggesting that assembly processes are largely neutral at this scale, likely the result of very high functional redundancy among species in the regional species pool.     

Community mean traits as additional indicators to monitor effects of land-use intensity on grassland plant diversity

Semi-natural grasslands, biodiversity hotspots in Central-Europe, suffer from the cessation of traditional land-use. Amount and intensity of these changes challenge current monitoring frameworks typically based on classic indicators such as selected target species or diversity indices. Indicators based on plant functional traits provide an interesting extension since they reflect ecological strategies at individual and ecological processes at community levels. They typically show convergent responses to gradients of land-use intensity over scales and regions, are more directly related to environmental drivers than diversity components themselves and enable detecting directional changes in whole community dynamics. However, probably due to their labor- and cost intensive assessment in the field, they have been rarely applied as indicators so far.Here we suggest overcoming these limitations by calculating indicators with plant traits derived from online accessible databases. Aiming to provide a minimal trait set to monitor effects of land-use intensification on plant diversity we investigated relationships between 12 community mean traits, 2 diversity indices and 6 predictors of land-use intensity within grassland communities of 3 different regions in Germany (part of the German ‘Biodiversity Exploratory’ research network). By standardization of traits and diversity measures, use of null models and linear mixed models we confirmed (i) strong links between functional community composition and plant diversity, (ii) that traits are closely related to land-use intensity, and (iii) that functional indicators are equally, or even more sensitive to land-use intensity than traditional diversity indices. The deduced trait set consisted of 5 traits, i.e., specific leaf area (SLA), leaf dry matter content (LDMC), seed release height, leaf distribution, and onset of flowering. These database derived traits enable the early detection of changes in community structure indicative for future diversity loss. As an addition to current monitoring measures they allow to better link environmental drivers to processes controlling community dynamics.     

A global meta‐analysis of the relative extent of intraspecific trait variation in plant communities

Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta‐analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole‐plant (e.g. plant height) vs. organ‐level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait‐based community and ecosystem studies.     

Abiotic drivers and plant traits explain landscape‐scale patterns in soil microbial communities

The controls on aboveground community composition and diversity have been extensively studied, but our understanding of the drivers of belowground microbial communities is relatively lacking, despite their importance for ecosystem functioning. In this study, we fitted statistical models to explain landscape‐scale variation in soil microbial community composition using data from 180 sites covering a broad range of grassland types, soil and climatic conditions in England. We found that variation in soil microbial communities was explained by abiotic factors like climate, pH and soil properties. Biotic factors, namely community‐weighted means (CWM) of plant functional traits, also explained variation in soil microbial communities. In particular, more bacterial‐dominated microbial communities were associated with exploitative plant traits versus fungal‐dominated communities with resource‐conservative traits, showing that plant functional traits and soil microbial communities are closely related at the landscape scale.     

吉林蛟河针阔混交林功能性状分布格局及其对地形因素的响应

森林群落的构建过程及其内在机制是生态学研究的热点问题。植物功能性状是指能够代表植物的生活史策略,反映植物对环境变化响应的一系列植物属性。通过植物功能性状的分布格局及其对环境因素的响应有助于推测群落的构建过程及其内在作用机制。以吉林蛟河21.12hm²温带针阔混交林样地为研究对象,采集并测量了样地内34种木本植物的6种不同的功能性状。以20m×20m的样方为研究单元,通过计算平均成对性状距离指数（mean pairwise trait distance;PW）和平均最近邻体性状距离指数（mean nearest neighbor trait distance;NN）来探讨群落中单个性状和综合性状的分布格局。同时结合地形因子采用回归分析探讨功能性状的分布格局对局域生境变化的响应。基于PW的结果显示：单个性状中除叶面积外,其余性状的分布格局均为聚集分布多于离散分布;基于NN的结果显示：除叶面积和最大树高外,其余性状的分布格局为聚集分布多于离散分布。此外,由6种单个性状组成的综合性状的分布格局同样为聚集分布多于离散分布。基于回归分析的结果显示：森林群落中功能性状的分布格局受到海拔、坡度和坡向等因素的显著影响,而凹凸度的影响则不显著。研究结果表明包括环境过滤和生物相互作用的非随机过程能够影响温带针阔混交林的群落构建过程,中性过程对该区域群落构建过程的影响不显著。     

Hierarchical effects of environmental filters on the functional structure of plant communities: a case study in the French Alps

Understanding the influence of the environment on the functional structure of ecological communities is essential to predict the response of biodiversity to global change drivers. Ecological theory suggests that multiple environmental factors shape local species assemblages by progressively filtering species from the regional species pool to local communities. These successive filters should influence the various components of community functional structure in different ways. In this paper, we tested the relative influence of multiple environmental filters on various metrics of plant functional trait structure (i.e. ‘community weighted mean trait’ and components of functional trait diversity, i.e. functional richness, evenness and divergence) in 82 vegetation plots in the Guisane Valley, French Alps. For the 211 sampled species we measured traits known to capture key aspects of ecological strategies amongst vascular plant species, i.e. leaf traits, plant height and seed mass (LHS). A comprehensive information theory framework, together with null model based resampling techniques, was used to test the various environmental effects. Particular community components of functional structure responded differently to various environmental gradients, especially concerning the spatial scale at which the environmental factors seem to operate. Environmental factors acting at a large spatial scale (e.g. temperature) were found to predominantly shape community weighted mean trait values, while fine‐scale factors (topography and soil characteristics) mostly influenced functional diversity and the distribution of trait values among the dominant species. Our results emphasize the hierarchical nature of ecological forces shaping local species assemblage: large‐scale environmental filters having a primary effect, i.e. selecting the pool of species adapted to a site, and then filters at finer scales determining species abundances and local species coexistence. This suggests that different components of functional community structure will respond differently to environmental change, so that predicting plant community responses will require a hierarchical multi‐facet approach.