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• Large intraspecific functional trait variation strongly impacts many aspects of communities and ecosystems, and is the medium upon which evolution works. Yet intraspecific trait variation is inconsistent and hard to predict across traits, species and locations. • We measured within-species variation in leaf mass per area (LMA), leaf dry matter content (LDMC), branch wood density (WD), and allocation to stem area vs leaf area in branches (branch Huber value (HV)) across the aridity range of seven Australian eucalypts and a co-occurring Acacia species to explore how traits and their variances change with aridity. • Within species, we found consistent increases in LMA, LDMC and WD and HV with increasing aridity, resulting in consistent trait coordination across leaves and branches. However, this coordination only emerged across sites with large climate differences. Unlike trait means, patterns of trait variance with aridity were mixed across populations and species. Only LDMC showed constrained trait variation in more xeric species and drier populations that could indicate limits to plasticity or heritable trait variation. • Our results highlight that climate can drive consistent within-species trait patterns, but that patterns might often be obscured by the complex nature of morphological traits, sampling incomplete species ranges or sampling confounded stress gradients

1. By comparing plant species under the same experimental field conditions, the direct effects of plant traits on ecosystem processes can be studied. We have analyzed the role of leaf traits (leaf lamina dry matter content, LDMC; leaf lamina N content, LNC and specific leaf lamina area, SLA) for the annual above-ground primary productivity (ANPP) and quality (pepsin-cellulase digestibility, crude protein content) for herbivores of 13 perennial C3 pasture grass species. 2. These relationships were investigated over 2 years with monocultures grown in a fully factorial block design crossing the plant species, the cutting frequency and the N supply factors. 3. The within species variation in leaf traits, ANPP, digestibility and protein content was less than between species variation. Species ranks for leaf traits were conserved among N supply and cutting frequency levels. Highly significant (P < 0-001) between species allometric relationships were found for LNC x SLA and SLA x LDMC, with common slopes but differences in intercept and shifts among factor levels. 4. The between species variation in ANPP was strongly (P < 0-001) and negatively correlated with the fresh-matter based leaf N content (i.e. LDMC x LNC) and was not affected by SLA, apparently because of a trade-off between SLA and leaf lamina fraction. Digestibility increased with SLA and declined with LDMC. Protein content increased with both fresh and dry-matter based LNC. 5. N supply increased LNC and SLA but reduced LDMC. Cutting frequency increased LDMC and reduced LNC. In response to cutting frequency, changes in digestibility and in fresh-matter based LNC were positively correlated. 6. We conclude that the between species variation in the annual production of digestible energy and of proteins by pasture grasses is controlled in an additive way by two leaf traits: LNC and LDMC.

• Understanding how plant communities respond to temporal patterns of precipitation in water-limited ecosystems is necessary to predict interannual variation and trends in ecosystem properties, including forage production, biogeochemical cycling, and biodiversity. • In North American shortgrass prairie, we measured plant abundance, functional traits related to growth rate and drought tolerance, and aboveground net primary productivity to identify: species-level responsiveness to precipitation (precipitation sensitivity S spp) across functional groups; S spp relationships to continuous plant traits; and whether continuous trait–S spp relationships scaled to the community level. • Across 32 plant species, we found strong bivariate relationships of both leaf dry matter content (LDMC) and leaf osmotic potential Ψosm with S spp. Yet, LDMC and specific leaf area were retained in the lowest Akaike information criterion multiple regression model, explaining 59% of S spp. Most relationships between continuous traits and S spp scaled to the community level but were often contingent on the presence/absence of particular species and/or land management at a site. • Thus, plant communities in shortgrass prairie may shift towards slower growing, more stress-resistant species in drought years and/or chronically drier climate. These findings highlight the importance of both leaf economic and drought tolerance traits in determining species and community responses to altered precipitation.

1. Understanding how environmental factors drive plant community assembly remains a major challenge in community ecology. The strength of different assembly processes along environmental gradients, such as environmental filtering and functional niche differentiation, can be quantified by analysing trait distributions in communities. While environmental filtering affects species occurrence among communities, functional divergence or convergence is strongly related to species abundances within communities, which few studies have taken into account. We examine the trait-mediated effect of these two processes along a stress-resource gradient. 2. We measured species abundances and the distributions of eight traits related to vegetative and regenerative phases in plant communities along a gradient of soil depth and resource availability in Mediterranean rangelands. We quantified environmental filtering, defined as a local restriction of trait range, and trait divergence, based on abundance-weighted trait variance, using a two-step approach with specifically designed null models. 3. Communities presented a clear functional response to the soil gradient, as evidenced by strong trends in community-weighted trait means. We detected environmental filtering of different traits at both ends of the gradient, suggesting that, contrary to widespread expectations, trait filtering may not necessarily be the result of abiotic filtering under harsh conditions but could likely also result from biotic interactions in productive habitats. 4. We found marked shifts in trait abundance distributions within communities along the gradient. Vegetative traits (e.g. leaf dry matter content) diverged on shallow soils, reflecting the coexistence of distinct water- and nutrient-use strategies in these constrained habitats and converged with increasing soil resource availability. By contrast, regenerative traits (e.g. seed mass) tended to diverge towards deeper soils, while plant reproductive heights diverged all along the gradient. 5. Synthesis: Our study highlights how the combination of abundance data with traits capturing different functional niches is critical to the detection of complex functional responses of plant communities to environmental gradients. We demonstrate that patterns of trait divergence and filtering are strongly contingent on both trait and environment such that there can be no expectation of a simple trend of increasing or decreasing functional divergence along a gradient of resource availability.

Soil pH varies by several units among ecosystems. While soil pH is known to be a key driver of plant species composition, we still have a poor understanding of how it affects carbon cycling processes. For instance, soil pH, or its associated chemistry in terms of base cations and organic acids, may affect decomposition rates of dead matter directly, by controlling decomposer composition and activity and, indirectly, by controlling the traits of the plant species and thereby the afterlife effects of those traits on litter decomposition. Leaf and litter pH may play a role in this control. Based on the very limited empirical data available, we hypothesized that variation in species traits including leaf (litter) pH, within and between ecosystems contrasting in soil pH, would have stronger effects on leaf litter decomposition rates than variation in soil chemistry would. We tested this hypothesis by carrying out a ‘common garden’ litterbed experiment in subtropical SW China, in which leaf litters of the 30 predominant plant species from mid‐successional forest on acidic sandstone (soil pH around 4.0) and calcareous soil (pH around 7.5), respectively, were incubated and their decomposition rates measured over two harvests in 14 months, both in soil plus litter matrix from their ‘home’ forest and in those from the ‘away’ forest. We found that leaf (litter) trait variation among species and plant functional types, headed by species' dry matter content but also including tissue pH, was the strongest driver of variation in leaf litter decomposition rates. Surprisingly, however, while these effects of interspecific trait variation were very strong among species from the same site, there was no overall difference in litter decomposability between the species from the acidic versus calcareous site. Equally surprising was that this strong difference in pH of soil substrate plus litter matrix from an acidic sandstone site versus a calcareous karst site did not directly affect leaf litter decomposition rates across a given species set. This first attempt to disentangle the multiple potential direct and indirect ways in which soil and leaf (litter) acidity might be related to litter decomposition rates has important implications for our understanding of soil–plant feedbacks. Based on our forest‐based study, we predict that soil–plant feedbacks via acidity are unlikely to be strong in ecosystems with wide‐ranging species in terms of their leaf functional traits, including leaf pH. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

1.Quantifying the variation in community-level fine root (<2mm) traits along ecological gradients or in response to disturbances is essential to unravel the mechanisms of plant community assembly, but available surveys are scarce. Whether fine root traits covary along a one-dimensional economic spectrum, as previously shown for leaves, is highly debated.2.We measured six fine root traits at the community-level along a 69-year succession, with or without annual mowing, offering a unique design of two nested disturbances. We examined whether (i) there is variation and covariation in community-level fine root traits along the succession and in response to mowing and (ii) morphological root traits mirrored analogous leaf traits (using previously acquired data).3.Early-successional communities were herbaceous-dominated (48±6% in <10 year old plots) and possessed fine roots with high specific root length (SRL), low root dry matter content (RDMC) and low root carbon concentration (RCC), while later-successional communities were dominated by woody species (56±9% in >40 year old plots) and possessed opposite trait values. Root nitrogen concentration (RNC) did not vary across communities along the succession. The trait values at community-level were not affected by mowing, except for a reduction in root mass density.4.We found covariation of fine root traits across communities along two dimensions: the first dimension (60% of total variation) represented changes in root foraging capacity (related to SRL) and resource conservation (related to RDMC, RCC, mean root diameter) whereas the second dimension (17 to 20% of the variation) represented variations in RNC, potentially related to root respiration and metabolism.5.SRL and SLA (specific leaf area) were correlated regardless of the mowing regime, but there was no analogous relationship between LDMC (leaf dry matter content) and RDMC in mown communities, showing a decoupling in the investment in tissue density above and belowground.6.Synthesis. Our study demonstrates coordinated variations of community-level fine root traits along a succession gradient and provides evidence that fine root traits covaried along two-dimensions, regardless of mowing regime. The relationship between LDMC and RDMC observed in unmown communities was modified by mowing, reflecting an uncoupled response to mowing.

Invertebrate herbivory can shape plant communities when impacting growth and fitness of some plant species more than other species. Previous studies showed that herbivory varies among plant species and that species-specific herbivory is affected by the diversity of the surrounding plant community. However, mechanisms underlying this variation are still poorly understood. In this study, we investigate how plant traits and plant apparency explain differences in herbivory among plant species and we explore the effect of plant community diversity on these species-specific relationships. We found that species differed in the herbivory they experienced. Forbs were three times more damaged by herbivores than grasses. Variability within grasses was caused by differences in leaf dry matter content (LDMC). Furthermore, higher plant diversity increased herbivory on 15 plant species and decreased herbivory on nine species. Variation within forb and grass species in their response to changing plant diversity was best explained by species’ physical resistance (LDMC, forbs) and biomass (grasses). Overall, our results show that herbivory and diversity effects on herbivory differ among species, and that, depending on the plant functional group, either species-specific traits or apparency are driving those differences. Thus, herbivores might selectively consume palatable forbs or abundant grasses with contrasting consequences for plant community composition in grasslands dominated by either forbs or grasses.

Is it possible to generalize relationships between certain plant traits and soil fertility? In particular, are there quantitative relationships between community-weighted mean (CWM) trait values of leaf dry-matter content (LDMC), specific leaf area (SLA), plant height, and Grime’s competitor-stress tolerator-ruderal (CSR) strategy scores and the generalized soil fertility, FG (i.e., the capacity of a soil to produce biomass when all nonsoil variables are held constant) that are generalizable across different species assemblages and geographical areas? We assessed FG in 21 sites in southern Quebec and 7 sites in southern France using a previously published method based on structural equation modeling. We then determined the CWM values of LDMC, SLA, plant height, and CSR scores in the 21 Quebec sites to obtain quantitative relationships between FG and these CWM traits. Using these relationships, we independently tested the generality of the trait–fertility relationships using data from French sites. The relationships between FG and the CWM traits were nonlinear, but displayed the expected qualitative trends as reported in the literature. In particular, the S score and CWM LDMC decreased with increasing soil fertility, and the R score and CWM SLA increased. CWM traits were more strongly correlated to measures of FG (r2 up to 0.48) than to measures of other soil characteristics (r2 up to 0.17 for nitrogen flux). Importantly, the independently tested French FG–trait relationships showed no significant deviations from these quantitative relationships. Further investigation is necessary to confirm if the same trend applies to other regions and or ecosystems.

The loss of plant functional diversity associated with biological invasion is a main subject of invasion biology, but still understudied in case of aquatic plants. We calculated functional richness, evenness, divergence and community-weighted mean trait values of aquatic plant communities for 20 plots, half invaded and half non-invaded by alien species, in a thermal effluent of West Hungary. Three traits [specific leaf area (SLA), leaf dry matter content (LDMC), leaf area (LA)] were considered to explain how alien species alter ecosystem function. We differentiated interspecific and intraspecific trait variation and investigate its effect on the community-level functional diversity. We found that alien species invasion causes significant changes in the functional composition of aquatic plants whereby alien species become able to absorb light more efficiently, which will directly enhance their increased biomass production. Our study highlights the importance of local adaptation, showing that calculating functional diversity with global pooling of trait measurements causes significant over- or underestimation of functional diversity indices. Consequently, this can potentially result in erroneous conclusions regarding the impact of invasion.

Here, we incorporate facilitation into trait-based community assembly theory by testing two mutually compatible facilitative mechanisms: changes in the environmental filter, causing either an increase in the range of trait values (i.e. a range expansion effect) and/or a shift in trait distributions (i.e. a range shift effect); and changes in trait spacing, suggesting an effect on niche differentiation. We analyzed the distribution of three functional traits – leaf dry matter content, specific leaf area and lateral spread – of plant communities dominated by a cushion-forming foundation species at four sites differing in elevation and aspect. We found support for environmental filtering and niche differentiation mechanisms by cushions, with filtering effects (in particular range shifts) increasing with environmental severity at higher elevation. The effect size of cushions on trait distribution was similar to that of environmental gradients caused by elevation and aspect. The consideration of intraspecific trait variability improved the detection of cushion effects on trait distributions. Our results highlight the importance of facilitation in the modification of taxonomic and functional diversity of ecological communities, and indicate that facilitation can occur through combined effects on environmental filtering and niche differentiation, with strong environmental context dependence of each mechanism.