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1.Ecosystem functioning relies heavily on belowground processes, which are largely regulated by plant fine-roots and their functional traits. However, our knowledge of fine-root trait distribution relies to date on local- and regional-scale studies with limited numbers of species, growth forms and environmental variation. 2.We compiled a worldwide fine-root trait dataset, featuring 1115 species from contrasting climatic areas, phylogeny and growth forms to test a series of hypotheses pertaining to the influence of plant functional types, soil and climate variables, and the degree of manipulation of plant growing conditions on species fine-root trait variation. Most particularly, we tested the competing hypotheses that fine-root traits typical of faster return on investment would be most strongly associated with conditions of limiting versus favourable soil resource availability. We accounted for both data source and species phylogenetic relatedness. 3.We demonstrate that (1) Climate conditions promoting soil fertility relate negatively to fine-root traits favouring fast soil resource acquisition, with a particularly strong positive effect of temperature on fine-root diameter and negative effect on specific root length (SRL), and a negative effect of rainfall on root nitrogen concentration; (2) Soil bulk density strongly influences species fine-root morphology, by favouring thicker, denser fine-roots; (3) Fine-roots from herbaceous species are on average finer and have higher SRL than those of woody species, and N2-fixing capacity positively relates to root nitrogen; (4) Plants growing in pots have higher SRL than those grown in the field. 4.Synthesis. This study reveals both the large variation in fine-root traits encountered globally and the relevance of several key plant functional types and soil and climate variables for explaining a substantial part of this variation. Climate, particularly temperature, and plant functional types were the two strongest predictors of fine-root trait variation. High trait variation occurred at local scales, suggesting that wide-ranging belowground resource economics strategies are viable within most climatic areas and soil conditions.

1. Cover crop mixtures with complementary plant functional traits including biological nitrogen fixation (BNF) may supply nitrogen (N) to farm fields while simultaneously providing other ecosystem functions such as N retention and weed suppression (i.e., multifunctionality). Understanding variation in these relationships across farms can help advance trait-based research in agroecology and ecological approaches to nutrient management. 2. This on-farm experiment explored the contributions of two- and three-species cover crop mixtures, which combined legumes, brassicas and cool season grasses, to ecosystem functions across a gradient of soil fertility levels driven by farm management history. 3. I evaluated the predictions that functional trait diversity of the cover crops would explain variation in multifunctionality, and that legume biomass and BNF within mixtures would be inversely correlated with indicators of soil N availability from organic matter across the farm gradient. 4. Ecosystem functions varied widely across farms. As expected, functional diversity was a significant predictor of multifunctionality, although the relationship was weak. Cover crop mixtures had significantly greater multifunctionality than a cereal rye monoculture, though not at the highest observed levels of each function, indicating trade-offs among functions. Linear regression models showed that legume biomass and BNF were negatively correlated with soil properties indicative of N availability from soil organic matter, whereas non-legume and weed biomass were positively correlated with other measures of soil fertility. 5. Synthesis and applications. Cover crop mixtures can increase functional diversity within crop rotations. Designing mixtures with complementary plant traits may be particularly effective for increasing multifunctionality and agroecosystem sustainability. On-farm research to understand variation in biological nitrogen fixation, which is both a plant trait and a key ecosystem function, across heterogeneous soil conditions, can inform management of soil fertility based on ecological principles.

Over half of the world's forests are disturbed, and the rate at which ecosystem processes recover after disturbance is important for the services these forests can provide. We analyze the drivers' underlying changes in rates of key ecosystem processes (biomass productivity, litter productivity, actual litter decomposition, and potential litter decomposition) during secondary succession after shifting cultivation in wet tropical forest of Mexico. We test the importance of three alternative drivers of ecosystem processes: vegetation biomass (vegetation quantity hypothesis), community-weighted trait mean (mass ratio hypothesis), and functional diversity (niche complementarity hypothesis) using structural equation modeling. This allows us to infer the relative importance of different mechanisms underlying ecosystem process recovery. Ecosystem process rates changed during succession, and the strongest driver was aboveground biomass for each of the processes. Productivity of aboveground stem biomass and leaf litter as well as actual litter decomposition increased with initial standing vegetation biomass, whereas potential litter decomposition decreased with standing biomass. Additionally, biomass productivity was positively affected by community-weighted mean of specific leaf area, and potential decomposition was positively affected by functional divergence, and negatively by community-weighted mean of leaf dry matter content. Our empirical results show that functional diversity and community-weighted means are of secondary importance for explaining changes in ecosystem process rates during tropical forest succession. Instead, simply, the amount of vegetation in a site is the major driver of changes, perhaps because there is a steep biomass buildup during succession that overrides more subtle effects of community functional properties on ecosystem processes. We recommend future studies in the field of biodiversity and ecosystem functioning to separate the effects of vegetation quality (community-weighted mean trait values and functional diversity) from those of vegetation quantity (biomass) on ecosystem processes and services.

1. The fast-slow plant economics spectrum predicts that because of evolutionary and biophysical constraints, different plant organs must be coordinated to converge in a unique ecological strategy within a continuum that shifts from fast to slow resource acquisition and conservation. Therefore, along a gradient of aridity, taxa with different strategies will be expected to be successful because selection pressures for slow resource acquisition become stronger as the environment becomes drier. In extremely arid and seasonal environments, however, a slow strategy may become disadvantageous because slow traits are costly to maintain. Additionally, as the availability of water decreases, selection pressures increase, reducing the variation in ecological strategies. 2. Using shrub assemblages along an aridity gradient in the Atacama Desert, we test the hypothesis that selection pressures imposed by hyper-aridity act simultaneously on the variation and coordination of trait attributes, leading to an inverse pattern in the fast-slow plant economics spectrum, where strategies shift from slow to fast as the environment becomes drier. 3. We established 20-22 plots at each of four sites along the gradient to estimate plant community structure and functional variation. For all species recorded, we quantified a set of leaf, stem, and root traits. 4. Results revealed an inverse pattern of the fast-slow economics spectrum for leaf and stem traits, but not for root traits; that is, as aridity further increased, aboveground traits exhibited a shift from a slow to a fast strategy with some level of coordination. Below-ground traits, however, did not shift accordingly with our prediction, rather they showed more complex pattern of shift and coordination with above-ground traits along the gradient. We also found that trait variation showed an idiosyncratic pattern of variation along the gradient, indicating that ecological strategies are driven by local processes within sites. 5. Synthesis. Our results increase our understanding of the fast-slow plant econom-ics spectrum by showing that environmental gradients, as well as local process can simultaneously shape different below- and above-ground resource acquisition strategies in extremely poor resource environments.

1. Human selection, changes in environmental conditions and management practices drove the phenotypic trajectory of crops during domestication. The characterization of the crop domestication syndrome lies mostly on reproductive characters. However, biophysical and ecophysiological constraints during vegetative growth are also at play and can strongly impact crop phenotypes. It has been argued that a broadened examination of crop phenotypes through a functional trait-based lens should improve our understanding of the domestication syndrome. 2. We used a collection of 39 genotypes representative of key steps during tetraploid wheat domestication and grew them in a common garden experiment. We quantified the vegetative phenotype of each genotype through the measurements of 13 functional traits related to root, leaf and whole-plant dimensions. 3. In modern cultivars, compared to ancestral forms, leaf longevity was shorter, while net photosynthetic rate, leaf production rate and nitrogen content were higher. Modern cultivars had a shallower root system and exhibited a larger proportion of fine roots, preferring to invest biomass above-rather than below-ground. We found ancestral forms to be integrated phenotypes characterized by coordination between above-and below-ground functioning. Conversely, in modern forms, human selection appeared to have broken this coordination and to have generated a new type of network of trait covariations. 4. Synthesis and applications. The examination of leaf, root and whole-plant traits of wheat accessions indicated a strong shift in plant functional strategies over the course of domestication. Elite genotypes tended to better optimize resource-use acquisition strategies than ancestral ones. The characterization of the crop phenotype based on vegetative traits thus suggests a much more complete domestication syndrome. Our findings highlight the benefits of using a functional trait-based characterization of crop phenotypes to document the extent of domestication syndrome and to further advance the agroecological management of cereals.

The insurance effect of biodiversity—that diversity stabilises aggregate ecosystem properties—is mechanistically underlain by inter‐ and intraspecific trait variation in organismal responses to the environment. This variation, termed response diversity, is therefore a potentially critical determinant of ecological stability. However, response diversity has yet to be widely quantified, possibly due to difficulties in its measurement. Even when it has been measured, approaches have varied. Here, we review methods for measuring response diversity and from them distil a methodological framework for quantifying response diversity from experimental and/or observational data, which can be practically applied in laboratory and field settings across a range of taxa. Previous empirical studies on response diversity most commonly invoke response traits as proxies aimed at capturing species' ecological responses to the environment. Our approach, which is based on environment‐dependent ecological responses to any biotic or abiotic environmental variable, is conceptually simple and robust to any form of environmental response, including nonlinear responses. Given its derivation from empirical data on species' ecological responses, this approach should more directly reflect response diversity than the trait‐based approach dominant in the literature. By capturing even subtle inter‐ or intraspecific variation in environmental responses, and environment dependencies in response diversity, we hope this framework will motivate tests of the diversity–stability relationship from a new perspective, and provide an approach for mapping, monitoring and conserving this critical dimension of biodiversity.

Deterministic theories predict that local communities assemble from a regional species pool based on niche differences, thus by plant functional adaptations. We tested whether functional traits can also explain patterns in species dominance among the suite of co‐occurring species. We predicted that along a gradient of secondary succession, the main driver of species dominance changes from environmental filtering in the relatively harsh (dry and hot) early successional conditions, towards increased competitive interactions and limiting similarity in later successional conditions (when light is limited). We used the Kurtosis (K) (a measure of peakedness) of the functional trait distribution of secondary forest communities in high‐diversity tropical rain forest in Chiapas, Mexico. The forests ranged 1–25 years in age, and we used eight functional leaf traits related to a plants' carbon, water and heat balance. We calculated the functional trait distribution based on species dominance, where trait values were weighted by species' relative basal area, as well as based on species presence, all species counting once. ‘K‐ratio’ was subsequently computed by dividing kurtosis based on species dominance by kurtosis based on species presence. If the K‐ratio is high, the dominant species are functionally similar and we interpreted this as environmentally driven functional convergence allowing species to become dominant. If the K‐ratio is small, dominant species are a functionally dissimilar subset of the species present and we interpreted this as competitively driven functional divergence allowing species to become dominant. We found that in early succession, dominant species represent a functionally narrow subset of species with similar traits, and in late succession, dominant species increasingly represent a wide subset of the species present. This trend was found for traits that reflect photosynthetic performance and light capture, and indicates increased competition for light with succession. No trend was found for traits that indicate defence against herbivory, suggesting no successional changes in herbivore pressure. Synthesis. This is one of the first studies showing that drivers of species dominance change along a gradient of secondary succession. During the early successional time window we evaluated, the importance of environmental filtering as a driving force fades away rapidly, and the importance of niche partitioning for species dominance starts to emerge.

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.

Questions The growth–survival trade‐off is a central concept for the conflicting strategies of acquisitive species that grow quicker and conservative species that grow slower. Understanding which, and how, cross‐species functional traits contribute to the growth–survival trade‐off is a key topic for understanding the functioning of tropical forests. The present study aimed to: (a) determine if leaf traits, wood density and fruit size influence the growth–survival trade‐off at the community level; and (b) test the hypothesis that averaged leaf traits, averaged wood density and averaged fruit size among all trees of subplots explain tree height in a 50‐ha plot of secondary Atlantic Forest in Brazil. Methods All trees with DBH > 3 cm had their heights estimated and were taxonomically identified. The functional traits used were leaf length (LL), leaf width (LW), petiole length (PL), petiole width (PW), leaf width/petiole width (LW/PW), leaf length × leaf width (LL*LW), wood density (WD), fruit length (FL) and fruit width (FW). Results A total of 74,335 trees of 178 species were recorded in 5,076 subplots of 100 m2. Associations between functional traits and mean height (Hmean) and height mode (Hmode) were congruent with expected trends of LW, LL, LW/PW, WD and FW with the top‐ranked global model explaining most of the found variance suggesting that Hmean and Hmode are the best averaged response variables. The growth response represented by Hmean and Hmode had the most distinctive, congruent and consistent association with LW/PW, WD and FW. Conclusions Higher LW and higher LW/PW indicated higher dependence of leaf blade on local microclimatic conditions, and lower dependence on petiole support for plant growth, which is beneficial for the acquisitive strategy. Smaller fruits and higher WD were also associated with the acquisitive strategy. Therefore, LW, LW/PW, WD and FW influenced the growth–survival trade‐off at the community level and explained tree height variation in the studied tropical forest. The growth–survival trade‐off is a central concept in plant ecology. The present study aimed to determine if leaf traits, wood density and fruit size influence the growth–survival trade‐off at the community level in a 50‐ha plot of secondary Atlantic Forest in Brazil. The overall growth response had the most consistent association with leaf width.

Leaf toughness is thought to enhance physical defense and leaf lifespan. Here, we evaluated the relative importance of tissue-level leaf traits vs lamina thickness, as well as their ontogenetic changes, for structure-level leaf toughness and regeneration ecology of 19 tropical tree species. We measured the fracture toughness of the laminas and veins of sapling leaves with shearing tests, and used principal component analysis and structural equation modeling to evaluate the multivariate relationships among traits that contribute to leaf toughness and their links to ecological performance traits. Tissue traits (density and fracture toughness of lamina and vein) were correlated positively with each other, but independent of lamina thickness. The tissue traits and lamina thickness contributed additively to the structure-level toughness (leaf mass per area and work-to-shear). Species with dense and tough leaves as saplings also had dense and tough leaves as seedlings and adults. The patterns of ontogenetic change in trait values differed between the seedling-to-sapling and sapling-to-adult transitions. The fracture toughness and tissue density of laminas and veins, but not the lamina thickness, were correlated positively with leaf lifespan and sapling survival, and negatively with herbivory rate and sapling regeneration light requirements, indicating the importance of tissue-level leaf traits.