Community-weighted Mean Trait Research Articles

Environmental controls override grazing effects on plant functional traits in Tibetan rangelands

AbstractPlant functional traits are key to predict community responses to abiotic and biotic disturbances. Grazing is the dominant land‐use form in drylands and alpine environments, especially in Central Asian rangelands. Here, we address grazing effects and their relative importance against environmental controls on plant traits.We sampled 14 plant functional traits, which are potentially sensitive to grazing, from 127 taxa distributed across three grassland types in Tibetan grasslands exposed to increasing levels of precipitation: steppe, steppe‐meadow and meadow. We performed principal components analysis and fourth‐corner analysis to explore the impacts of grazing and environment on multiple community‐weighted mean (CWM) traits. We also used generaliszed linear mixed models to test the effects of grazing and environment on each CWM trait, and on three dimensions of functional trait diversity, i.e. functional richness (FRic), evenness (FEve) and divergence (FDiv). In addition, we undertook a mini‐review of former studies on grazing effects on plant traits in Chinese grasslands.We found that CWM traits were mainly affected by climate and elevation rather than by grazing intensity. Only plant tissue C content was negatively affected by intensified grazing across grassland types. Plant growth form and life form were mainly influenced by elevation, while heights of canopy and inflorescence were controlled by temperature. Specific leaf area was positively correlated with precipitation and soil total N content in steppes, while plant tissue N content was only correlated to livestock dung cover. Regarding functional trait diversity, FDiv in steppe‐meadows and meadows, and FEve in meadows were reduced by grazing.Synthesis. Our results confirmed that environmental controls override grazing impact on CWM traits across Tibetan alpine grasslands. Most plants and their respective traits are adaptive to alpine climates as well as to grazing, and are thus hardly affected by locally intensified grazing intensity. In steppes, functional diversity is insensitive to grazing due to the combined stress of drought and grazing. However, in steppe‐meadows and meadows, grazing may affect ecosystem functioning, as shown by the reduced values of FDiv and FEve under more intense grazing.A freePlain Language Summarycan be found within the Supporting Information of this article.

Effects of tree functional diversity and environmental gradients on belowground biomass in a natural old-growth forest ecosystem

The positive effects of biodiversity on aboveground biomass in natural terrestrial ecosystems have been well documented, whereas the relationships between tree biodiversity and belowground biomass remain largely unexplored. Traditionally, two sets of hypotheses based on the functional trait approach, niche complementarity (NC) and mass ratio (MR), have been proposed to explain the positive effects of biodiversity. Whereas NC emphasizes that functional discrepancy enhances the collective functioning of a given ecosystem, MR states that ecosystem functioning is mainly regulated by the functional traits of dominant species. This study explored the relative importance of these two hypotheses and the effects of forest stand and environmental characteristics on belowground biomass in an old-growth broad-leaved evergreen forest. The mean coarse-root biomass, fine-root biomass, and fine-root necromass were 117.78 ± 54.000, 4.09 ± 0.85, and 0.60 ± 0.31 Mg·ha−1, respectively. We found positive effects of functional diversity on belowground biomass; however, the community-weighted mean trait values were more relevant, indicating that MR exhibited more explanatory power than NC. The combination of informative environmental factors explained 62.0%, 53.2%, and 37.8% of the variation of coarse-root biomass, fine-root biomass, and fine-root necromass, respectively. Our results suggest that the functional identity of dominant tree species exerts more influence than functional diversity on the belowground biomass in old-growth forest ecosystems and that forest stand characteristics and topographic and edaphic factors also play important roles in shaping belowground biomass patterns in old-growth forest ecosystems.

Multiple facets of diversity effects on plant productivity: Species richness, functional diversity, species identity and intraspecific competition

Abstract Deciphering the mechanisms that drive variation in biomass production across plant communities of contrasting species composition and diversity is a main challenge of biodiversity–ecosystem functioning research. Niche complementarity and selection effect have been widely investigated to address biodiversity–productivity relationships. However, the overlooking of the specific role played by key species has limited so far our capacity to comprehensively assess the relative importance of other potential drivers of biodiversity effects. Here, we conducted a grassland diversity–productivity experiment to test how four potential facets of biodiversity effects, namely species richness, functional diversity, species identity and the relaxation of intraspecific competition, account for variations in above and root biomass production. We grew six plant species in monoculture, as well as in every combination of two, three and six species. Plant density was kept constant across the richness gradient but we additionally grew each species in half‐density monoculture to estimate the strength of intraspecific competition for each studied species. We characterized eight functional traits, including root traits, related to nutrient and light acquisition and computed both the functional dissimilarity and the community‐weighted mean (CWM) of each trait. We further partitioned above‐ground biodiversity effect into complementarity and selection effects. We observed strong positive biodiversity effects on both above‐ground and root biomass as well as strong positive complementarity effect. These arose largely from the presence of a particular species (Plantago lanceolata) and from CWM trait values more than from a higher functional dissimilarity in plant mixtures. P. lanceolata displayed the highest intraspecific competition, which was strongly relaxed in species mixtures. By contrast, the presence of Sanguisorba minor negatively affected the productivity of plant mixtures, this species suffering more from interspecific than intraspecific competition. This study provides strong evidences that the search for key species is critical to understand the role of species diversity on ecosystem functioning and demonstrates the major role that the balance between intraspecific and interspecific competition plays in biodiversity–ecosystem functioning relationships. Developing more integrative approaches in community and ecosystem ecology can offer opportunities to better understand the role that species diversity plays on ecosystem functioning. A free Plain Language Summary can be found within the Supporting Information of this article.

Association of Community-level Traits with Soil Properties in a Tropical Coastal Sand Dune

There is limited information regarding plant functional traits for plant communities in tropical coastal sand dunes. This study investigated differences in species trait compositions and the relationship between community-weighted mean (CWM) traits and soil properties on the windward and leeward sides of the Bang Boet coastal sand dunes in southern Thailand. Ten sampling plots were randomly selected from each side of the dune. All woody plant species were collected and their functional traits were assessed. Soil samples were also collected. A redundancy analysis (RDA) was used to examine the relationship between CWM traits and soil properties. The results showed that species trait compositions and the CWMs of specific leaf area, leaf thickness, and leaf toughness were significantly different between windward and leeward sides. The RDA showed significant correlation between CWM traits and soil properties, particularly for specific leaf area, a functional trait that plays an important role in nutrient turnover on the leeward side. These results indicate that soil properties are predictable based on CWM traits and that leeward sand dune sides can support greater soil formation than windward sides. Hence, functional traits, as well as species, should be considered in coastal sand dune restoration and conservation programs.

From local to regional: Functional diversity in differently managed alpine grasslands

Increasing evidence suggests that ecosystem functions are strongly linked to morphological plant traits, like specific leaf area (SLA) and its variability, which serve as a proxy of functional diversity (FD). Functional diversity is rarely studied at regional scales, and its scale dependence is poorly understood. Capturing trait variations at distinct spatial scales and in differently managed grasslands remains challenging, mainly because a limited number of trait measurements are available and field campaigns are time-consuming. Here, we derived α- and β-FD indices based on SLA measured in the field and estimated from optical satellite data by using molecular absorption profiles of leaves in canopies. We inverted the 1-D columnar radiative transfer model PROSAIL using Sentinel-2 reflectance data at canopy level. From the inversion we were able to distinguish different alpine management types based on retrieved SLA. Model uncertainties were mainly related to the different local plant communities, here represented by functional diversity indices and community-weighted means of traits. Thus, successful PROSAIL application was affected by management type. Management categories displaying lower α-FD, like mowed and fertilized, delivered the most reliable results. Further, we compared FD (i.e., richness, evenness, divergence) from local to regional scales. Locally, management determines the magnitude of FD, whereas on a regional scale, parcel size and the uniformity of agricultural practices control trait diversity. Our results highlight the importance of quantifying β-FD from space as it delivers additional information on the impact of management types, differing from locally measured α-FD values.

Influence of tree functional diversity and stand environment on fine root biomass and necromass in four types of evergreen broad-leaved forests

Positive effects of tree diversity on above-ground biomass have been well documented, whereas the relationships between tree functional diversity and fine root biomass and necromass remain unclear. This study explored the variation in fine root biomass and necromass among different evergreen broad-leaved forest types, the relative importance of the niche complementarity and the mass ratio hypotheses in driving biodiversity effects, as well as forest stand attributes and environmental factors causing variation in fine root biomass and necromass. We detected no significant differences between most forest types, and the prominently lower amount of fine root biomass and necromass in monsoon evergreen broad-leaved forests may be ascribed to the accelerated turnover rate caused by the elevated temperature. Conversely, the functional divergence showed marginally positive effects on fine root necromass, hence the effects of functional diversity may be negligible; however, community-weighted mean trait values, i.e. specific leaf area and leaf phosphorus concentration, demonstrated significantly negative effects on them. Basal area and stem density showed significant influence in regulating fine root biomass. The optimal GAM models explained 79.5% and 54.4% of the variation of fine root biomass and necromass, respectively. Our results suggest that fine root biomass and necromass may be determined by the functional characteristics of dominant tree species rather than collective functional diversity and closely linked to forest stand, topographic and edaphic factors.

Linking Aboveground Traits to Root Traits and Local Environment: Implications of the Plant Economics Spectrum.

The plant economics spectrum proposes that ecological traits are functionally coordinated and adapt along environmental gradients. However, empirical evidence is mixed about whether aboveground and root traits are consistently linked and which environmental factors drive functional responses. Here we measure the strength of relationships between aboveground and root traits, and examine whether community-weighted mean trait values are adapted along gradients of light and soil fertility, based on the seedling censuses of 57 species in a subtropical forest. We found that aboveground traits were good predictors of root traits; specific leaf area, dry matter, nitrogen and phosphorus content were strongly correlated with root tissue density and specific root length. Traits showed patterns of adaptation along the gradients of soil fertility and light; species with fast resource-acquisitive strategies were more strongly associated with high soil phosphorus, potassium, openness, and with low nitrogen, organic matter conditions. This demonstrates the potential to estimate belowground traits from known aboveground traits in seedling communities, and suggests that soil fertility is one of the main factors driving functional responses. Our results extend our understanding of how ecological strategies shape potential responses of plant communities to environmental change.

Applying continuous functional traits to large brown macroalgae: variation across tidal emersion and wave exposure gradients

Ecologists use a functional trait-based approach to seek a general understanding of organism—environment interactions, but, among primary producers, the empirical basis rests on vascular plants. We hypothesised that with increasing intertidal elevation, traits of large brown macroalgae would reflect a resource acquisition vs. conservation (stress tolerance) trade-off at species and community levels. Across the elevation gradient at four UK sites of varying wave exposure, we: (1) screened species’ relevant morphological traits, using principal component analysis to reduce dimensionality; and (2) up-scaled species’ traits using community weighted trait means (CWMs). The first principal component (PC1) strongly related to specific thallus area and thallus dry matter content, representing an acquisition–conservation trade-off. Although species generally shifted to the conservative end of this axis as elevation increased, mid-shore Ascophyllum nodosum sat at the extreme conservative end. PC2 related to holdfast ratio, thickness and length, with A. nodosum scoring higher than other mid-shore species. CWMs of PC1 decreased with elevation at two sites indicating a shift from ‘fast’ to ‘slow’ ecosystem functioning, but this relationship was disrupted by A. nodosum at the sheltered site, and by the up-shore extent of Laminaria digitata at the most exposed site. The anomalous traits of A. nodosum reflect its unique competitive strategy (slow, persistent growth) in the relatively stressful mid-shore. Seaweed functional traits show promise in linking species’ identities to their strategies and ecosystem contributions. However, because resource conservation traits can be related to competitive as well as stress-tolerance strategies, predicting seaweed trait responses to environmental stress gradients is challenging.

Effects of climate, soil, forest structure and land use on the functional composition of the understorey in Italian forests

AbstractQuestionIn functional biogeography studies, generalizable patterns in the relationship between plant traits and the environment have yet to emerge. Local drivers (i.e., soil, land use, vegetation structure) can increase our understanding of the trait–environment relationship. What is the role of climate and local drivers in shaping abundance‐weighted trait patterns of forest understories at biogeographic scales?LocationItalian forests.MethodsWe selected 201 sites that are statistically representative for the heterogeneity of Italian forests across three biogeographic regions (alpine, continental, and mediterranean). Understorey vegetation was recorded for each site on an area of 400 m2, together with 25 environmental variables related to climate, soil, land use and forest structure. Specific leaf area (SLA), plant height (H) and seed mass (SM) were obtained from databases. Community‐weighted mean (CWM) values were calculated. Variance partitioning was used to identify the relative role of groups of environmental variables on the CWM of traits. Generalized Additive Models were used to assess the relationship between traits and single variables.ResultsClimate alone and climate–soil interactions explained the largest proportion of the variation of all the traits (13.7% to 22.8%). Temperature‐related factors as well as soil N and P availability were the climatic and edaphic explanatory variables most correlated to trait variation. Forest structure and land use accounted for a smaller percentage of the variation in traits. Land‐use factors alone were important in explaining only SLA variation.ConclusionsWhile climate plays a major role in trait–environment relationships in forest understories, our results highlighted the need to integrate at least soil properties as local drivers of trait variation in broad scale functional biogeography studies of these systems.

Environmental structure affects taxonomic diversity but not functional structure of understory birds in the southwestern Brazilian Amazon

ABSTRACT Changes in environmental characteristics can affect habitat use by birds, impacting the number of individuals, number of species, and changing species composition and functional structure of assemblages. Metrics that evaluate the functional structure of biological assemblages constitute a complementary tool to the traditional taxonomic approach, because they quantify the differences between species by means of functional traits. We assessed the effect of environmental characteristics on the taxonomic diversity (species richness, species composition and number of individuals) and functional structure (functional richness, functional evenness, Rao’s functional diversity, and community-weighted mean traits) of bird assemblages in northern Mato Grosso state, in the southwestern Brazilian Amazon. We sampled birds in 32 plots. At each plot birds were captured using mist nets, and eight environmental variables were measured: canopy openness, leaf litter, elevation, number of trees in three classes of DBH, soil clay content, and distance to nearest stream. To evaluate functional structure, we measured seven morphological traits from individuals of each bird species. Habitat variables had a significant effect on taxonomic diversity. However, the general functional structure was not affected. Elevation and distance to nearest stream were the main variables driving changes in taxonomic diversity and had a minor effect on functional richness. The other metrics of functional structure were not significantly affected by the set of environmental variables. Our results suggest that the sampled bird assemblages exhibit some functional tolerance (redundancy) to small-scale environmental variation, implying certain resilience to ecosystem modification.

Shifts in plant functional composition following long‐term drought in grasslands

AbstractPlant traits can provide unique insights into plant performance at the community scale. Functional composition, defined by both functional diversity and community‐weighted trait means (CWMs), can affect the stability of above‐ground net primary production (ANPP) in response to climate extremes. Further complexity arises, however, when functional composition itself responds to environmental change. The duration of climate extremes, such as drought, is expected to increase with rising global temperatures; thus, understanding the impacts of long‐term drought on functional composition and the corresponding effect that has on ecosystem function could improve predictions of ecosystem sensitivity to climate change.We experimentally reduced growing season precipitation by 66% across six temperate grasslands for 4 years and measured changes in three indices of functional diversity (functional dispersion, richness and evenness), community‐weighted trait means and phylogenetic diversity (PD). Specific leaf area (SLA), leaf nitrogen content (LNC) and (at most sites) leaf turgor loss point (πTLP) were measured for species cumulatively representing ~90% plant cover at each site.Long‐term drought led to increased community functional dispersion in three sites, with negligible effects on the remaining sites. Species re‐ordering following the mortality/senescence of dominant species was the main driver of increased functional dispersion. The response of functional diversity was not consistently matched by changes in phylogenetic diversity. Community‐level drought strategies (assessed as CWMs) largely shifted from drought tolerance to drought avoidance and/or escape strategies, as evidenced by higher community‐weightedπTLP, SLA and LNC. Lastly, ecosystem drought sensitivity (i.e. relative reduction in ANPP in drought plots) was positively correlated with community‐weighted SLA and negatively correlated with functional diversity.Synthesis.Increased functional diversity following long‐term drought may stabilize ecosystem functioning in response to future drought. However, shifts in community‐scale drought strategies may increase ecosystem drought sensitivity, depending on the nature and timing of drought. Thus, our results highlight the importance of considering both functional diversity and abundance‐weighted traits means of plant communities as their collective effect may either stabilize or enhance ecosystem sensitivity to drought.

Leaf traits of macrophytes in lakes: Interspecific, plant group and community patterns

In freshwater systems the differentiation between macrophyte groups and growth forms is evident. The plant functional approach was used to understand the patterns of traits seen in the macrophytes of lakes at three levels: interspecific, functional groups and communities. Leaf area (LA), leaf dry weight (LDW) and specific leaf area (SLA) were measured for 31 macrophyte species in 30 lakes in Poland. To investigate the community structure, aquatic macrophyte species were sampled in 30 lakes 100 along 145 sections at the bottoms of the lakes (depth zones at 1.0 m). In total, we collected 14 500 cover-plant samples (quadrat, area = 0.1 m2). For each sample, we estimated the coverage (%) of species by SCUBA diving. Leaf trait variation was examined via mean or community-weighted mean (CWM) comparisons at three levels: interspecific, species grouped into plant functional groups (FGs) and communities. Shifts in leaf trait values were found at the interspecific and FG levels. LA, LDW and SLA varied widely across the 31 macrophyte species and among functional groups. Our results show that there are differences between CWM trait values (LDW, LA) among communities. In summary, we found that SLA decreased with increased water pH and calcium content interspecifically and among communities. Our findings show that different functional patterns predict the functioning of plant communities and FGs in lakes. Furthermore, the diversity in functional traits appears to be part of community assembly for macrophytes. At the functional group level, there are shifts in leaf traits. In contrast, among communities, there are low variations in leaf traits.

Leaf Nutrients and Macroinvertebrates Control Litter Mixing Effects on Decomposition in Temperate Streams

Plant litter decomposition is an essential ecosystem function in temperate streams. Both riparian vegetation and decomposer communities are major determinants of the decomposition efficiency and the interactions occurring within litter mixtures. However, the extent to which such litter mixture interactions are affected by combined shifts in litter traits and decomposer community is not well understood. We used leaf litter from 10 European tree species in order to study litter decomposition and litter mixture effects occurring in two-species litter mixtures in a temperate forested stream of northwestern France. The study distinguished between (1) decomposition involving microorganisms alone or together with invertebrates, and (2) decomposition involving litter mixtures of similar or dissimilar nutrient content. Increasing mean litter nutrient concentration favored both microbial activity and litter decomposition rate. Surprisingly, the highest litter mixture effects occurred in mixtures containing two nutrient-rich litters and occurred mainly in macroinvertebrate presence. Both the “mass ratio hypothesis,” expressed as the community-weighted mean traits (TraitCWM), and the “niche complementarity hypothesis,” expressed as the functional dissimilarity of litter traits (TraitFD), contributed to explain litter mixture effects. However, TraitCWM was found to be a better predictor than TraitFD. Finally, when evaluating the individual contributions of litter nutrients, calcium and magnesium appeared as important drivers of litter mixture effects. Our findings suggest that the mass ratio hypothesis overrules the niche complementarity hypothesis as a driver of litter diversity effects. Our study highlights the key importance of macroinvertebrates and of leaf nutrients, such as Ca and Mg, which are often neglected in decomposition studies in streams.

Plant functional diversity drives carbon storage following vegetation restoration in Loess Plateau, China

Ongoing climatic changes induced by human activities increases in atmospheric carbon dioxide (CO2), which have considerable effects on the structure and function of ecosystems, including carbon (C) storage, plant functional traits and therefore on a wide set of ecosystem services. Plant functional diversity is benefit to improve plant photosynthesis and enhance C efficiency and therefore decrease CO2. Here, the focus of this article is on integrating of plant functional diversity and C storage, which aims to contribute to C sequestration for climate change mitigation following vegetation restoration in Loess Plateau, China. Firstly, the CWM (plant community-weighted mean) traits of the most abundant plant species can account for C storage in AGBC (above-ground biomass C), ALC (above-ground litter C), STC (soil total carbon) and TEC (total ecosystem carbon). Secondly, the CWM of plant height and LCC (leaf carbon concentration) had a positive effect C storage in different part (AGBC, ALC, STC and TEC), while the CWM of LNC (leaf nitrogen concentration) and SLA (specific leaf area) had a negative effect on C storage in different part. Further, the CWM of plant height, LCC, SLA and plant functional dispersion (FDis) can be used to predict C storage by multiple linear regression analysis. Finally, the positive association between FDis and C storage was found in SEM, shedding light on the key role of plant functional diversity driving C storage following vegetation restoration. The findings presented here highlight the importance of both plant traits of dominant species and plant functional diversity in regulating C storage, and show that favorable climate conditions, particularly vegetation restoration, tend to increase C storage and plant functional diversity, which have important implications for improving global C cycling and ecosystem services.

Functional diversity overrides community-weighted mean traits in linking land-use intensity to hydrological ecosystem services

Land-use intensification can importantly influence terrestrial ecosystem services by altering plant functional traits. Although we know that functional traits influence both ecosystem properties and services, we do not fully understand the mechanistic pathways governing these relationships nor how they will respond to global climate change. To identify the impact pathways of land-use intensity on hydrological services under changing precipitation regimes, we monitored hydrological services in 15 plots of different land-use types during 25 precipitation events (6 light, 8 moderate, and 11 heavy rains). Bayesian structural equation modeling was used to quantify the direct and indirect effects between land-use intensity, functional trait components (community weighted mean [CWM] and functional diversity [FD]), ecosystem properties (canopy density, litter fall and fine-root density), and hydrological services under different rainfall intensities. The impact of land-use intensity on hydrological service provisioning was regulated by plant functional traits regardless of intensity rainfall. Under light and moderate rain, FD significantly influenced hydrological services by altering canopy density and fine-root density, but we found no significant effect of CWMs. Under heavy rain, FD had significant, and greater, impacts on hydrological services than CWM of traits, although CWM of traits influenced hydrological services provision indirectly by altering canopy density and fine-root density. Land-use intensity indirectly affected hydrological services mainly by altering FD regardless of rainfall intensification, suggesting that the reduction of niche differentiation caused by land-use intensity is the main mechanism of hydrological services degradation. Our results suggested that the effect of land-use intensity on hydrological services are likely to change with increasing frequency of extreme precipitation events because of the different underlying mechanism at play and emphasize the importance of FD in maintaining hydrological services in respond to global environmental changes.

Plant Traits Rather than Species Richness Explain Ecological Processes in Subtropical Forests

Functional traits and species richness have been used to assess variation in ecological functions in multiple ecosystems. However, biodiversity effects on ecosystem functioning could differ between ecosystem types and evaluating these associations could help assess ecosystem recovery in restoration sites. The objective of this study was to analyze the effect of species richness and plant functional traits on ecological processes related to nutrient cycling, productivity and regeneration in subtropical forest ecosystems. The study was performed in three sites (each site containing a reference forest and a forest undergoing restoration) located in the south of Brazil. We collected data on understory abundance, aboveground biomass, litter stock, decomposition, soil feeding activity, litter and soil quality and evaluated the association with tree species richness and plant traits (both community-weighted mean trait values—CWM, and functional diversity measures). Variables related to plant functional traits, especially CWM measures, were associated with most of the ecological processes analyzed. Leaf traits showed the strongest effect on the processes, especially for aboveground biomass, litter stock and understory abundance. Most relationships did not differ between reference and restoration sites. Our results support the mass-ratio theory, suggesting that dominant species traits are the ones that strongly affect ecosystem functioning, and suggest a secondary role of species number on the ecological processes analyzed. Our study provides evidence for the usefulness of functional traits to assess changes in ecological processes in forest ecosystems, with similar patterns in reference forests and forests undergoing restoration.

Effect of monospecific and mixed Mediterranean tree plantations on soil microbial community and biochemical functioning

Soil microbial communities (SMCs) are important drivers of forest ecosystem functions and services. To optimize afforestation practices, it is important to understand how pure and mixed plantations can affect SMCs and their functioning. Therefore, the objective of this work was to investigate the SMC structure and function of six Mediterranean woody species grown as monocultures, and of six selected 1:1 combinations. SMC structure was assessed through the abundance estimation of different culturable heterotrophic microbial populations (i.e. bacteria, fungi, actinomycetes, Pseudomoas spp. and aerobic spore-forming bacteria) and the Biolog community level physiological profile, while soil biochemical functioning was estimated by quantifying soil dehydrogenase (DHG) activity.Species richness (SR) did not increase the abundance of culturable heterotrophic microbial populations, nor the number of carbon sources metabolized by the microbial communities (Biolog richness) or DHG activity. However, SR significantly decreased the potential metabolic activity (Biolog AWCD) of soil microbial populations. Leaf type significantly affected soil microbial and biochemical features, particularly for monocultures where conifer plots were characterized by a significantly higher fungal/bacterial ratio, reduced AWCD and richness as well as reduced DHG values. Significant interactions between tree species in mixed plots were noticed as well as significant correlations between plant community weighted mean (CWM) traits and soil microbial and biochemical features. Both SMC structure and function were clearly influenced by tree plantations and, importantly, microbial populations of monocultures and mixed plantations, and their functioning, were governed by different CWM traits.

Responses of plant leaf economic and hydraulic traits mediate the effects of early- and late-season drought on grassland productivity.

Drought can occur at different times during the grassland growing season, likely having contrasting effects on forage production when happening early or later in the season. However, knowledge about the interacting effects of the timing of drought and the development stage of the vegetation during the growing season is still scarce, thus limiting our ability to accurately predict forage quantity losses. To investigate plant community responses to drought seasonality (early- vs. late-season), we established a drought experiment in two permanent grasslands of the Swiss Jura Mountains that are used for forage production. We measured three plant functional traits, including two leaf traits related to plant economics (specific leaf area, SLA; leaf dry matter content, LDMC) and one hydraulic trait related to physiological function (predicted percentage loss of hydraulic conductance, PLCp), of the most abundant species, and plant above-ground biomass production. Plant species composition was also determined to calculate community-weighted mean (CWM) traits. First, we observed that CWM trait values strongly varied during the growing season. Second, we found that late-season drought had stronger effects on CWM trait values than early-season drought and that the plant hydraulic trait was the most variable functional trait. Using a structural equation model, we also showed that reduction in soil moisture had no direct impacts on above-ground biomass production. Instead, we observed that the drought-induced decrease in above-ground biomass production was mediated by a higher CWM PLCp (i.e. higher risk of hydraulic failure) and lower CWM SLA under drought. Change in CWM SLA in response to drought was the best predictor of community above-ground biomass production. Our findings reveal the importance of drought timing together with the plant trait responses to assess drought impacts on grassland biomass production and suggest that incorporating these factors into mechanistic models could considerably improve predictions of climate change impacts.

A height-wood-seed axis which is preserved across climatic regions explains tree dominance in European forest communities

Environmental constraints on both functional traits and trait–trait correlation patterns are extremely relevant research questions to understand assembling mechanisms and scaling processes in ecology. In fact, community weighted mean (CWM) and functional diversity (FD) metrics assimilate meaningful complementary information from species to community level. Relating species abundance data from national forest inventories (France, Italy and Spain) with species trait values from published sources, we explored CWM and FD variations along climatic gradients for traits related to leaf, hydraulic and live history strategies, and how the CWM or the FD of single traits co-vary. Results show how the combined effects of water availability and temperature modulate CWM, and to a lower extent FD, of Western European forests. PCA on CWM traits data showed that main axis accounts for 46.6% of the variability and is represented by wood density, seed dry weight (SDW) and maximum height. This axis is similarly preserved in humid and dry areas and potentially related to competition ability, growth rates and successional status of tree species dominants. Furthermore, the second axis is associated with leaf wilting and cavitation resistance (P50), but not consistent in dry areas. Correlation patterns of FD data, which were partially preserved across climatic regions, showed one main axis involving the joint variability of all traits. However, between humid and dry areas determinants of SDW and P50 differ from all other traits. Results showed that at least a part of the co-variation patterns among traits change with climate conditions, suggesting scale-dependent effects which should be taken into account when scaling assembly mechanisms.

Functional diversity along elevational gradients in the high altitude vegetation of the western Himalaya

The analysis of species distribution and functional diversity (FD) in natural gradients of aridity and temperature at high altitudes could provide indication of future changes in plant communities as both are responsive to environment and strongly influence ecosystem functioning and stability. We established eleven altitudinal transects in high altitude region of western Himalaya, six of which represented north aspect and the rest represented south aspect. In each transect, vegetation was sampled randomly at every 200 m elevation to estimate species rarity, niche width and different FD indices [community-weighted mean traits (CWM), functional richness (FRic), functional divergence (FDiv), functional dispersion (FDis) and functional specificity (FSpe)]. These indices indicate resource utilization, competition for resources, optimal plant strategies, and presence of functionally specialist species. We found a total of 418 plant species, most of which were having narrow niche and distribution. Proportion of species with narrow niche was high at higher elevations, 36.5% species were rare with 17% of them being endemic to Himalaya. At south aspect, lower values of CWM plant height along with lower FRic, FDiv, FDis, and FSpe were recorded. Further, CWM plant height, FRic, FDiv, FDis and FSpe significantly decreased with increasing elevation. Influence of gradients of aridity (aspect) and decreasing temperature (elevation) on species distribution and FD suggest that functioning of high altitude communities is very likely to be affected in future. Our findings therefore emphasize that the plant communities present at higher elevations are more vulnerable under climate change.