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Abstract Environmental gradients act as potent filters on species distributions driving compositional shifts across communities. Compositional shifts may reflect differences in physiological tolerances to a limiting resource that result in broad distributions for tolerant species and restricted distributions for intolerant species (i.e. a nested pattern). Alternatively, trade‐offs in resource use or conflicting species' responses to multiple resources can result in complete turnover of species along gradients.We combined trait (leaf area, leaf mass per area, wood density and maximum height) and distribution data for 550 tree species to examine taxonomic and functional composition at 72 sites across strong gradients of soil phosphorus (P) and rainfall in central Panama.We determined whether functional and taxonomic composition was nested or turned over completely and whether community mean traits and species composition were more strongly driven by P or moisture.Turnover characterized the functional composition of tree communities. Leaf traits responded to both gradients, with species having larger and thinner leaves in drier and more fertile sites than in wetter and less fertile sites. These leaf trait–moisture relationships contradict predictions based on drought responses and suggest a greater role for differences in light availability than in moisture. Shifts in wood density and maximum height were weaker than for leaf traits with taller species dominating wet sites and low wood density species dominating P‐rich sites.Turnover characterized the taxonomic composition of tree communities. Geographic distances explained a larger fraction of variation for taxonomic composition than for functional composition, and community mean traits were more strongly driven by P than moisture.Synthesis. Our results offer weak support for the tolerance hypothesis for tree communities in central Panama. Instead, we observe functional and taxonomic turnover reflecting trade‐offs and conflicting species' responses to multiple abiotic factors including moisture, soil phosphorus and potentially other correlated variables (e.g. light). 

Abstract Phylogenetic and species‐based taxonomic descriptions of community structure may provide complementary information about the mechanisms driving community assembly across different environments. Environmental filtering may have similar effects on taxonomic and phylogenetic diversity under the assumption of niche conservatism, whereas competitive exclusion could produce contrasting patterns in these diversity metrics. In grassland restorations, these diversity patterns might then reveal potential assembly mechanisms underlying the impacts of restoration and management conditions on community structure.We compared plant community structure (alpha diversity, composition, and within‐site beta diversity) from both phylogenetic and taxonomic perspectives. Using surveys from 120 tallgrass prairie restorations in four regions of the Midwestern United States, we examined the effects of four potential drivers or environmental gradients: precipitation in the first year of restoration, seed mix richness, time since last prescribed fire, and restoration age, and included soil conditions as a covariate.First‐year precipitation influenced taxonomic community structure, but had weak effects on phylogenetic diversity and composition. Similarly, greater seed mix richness increased taxonomic diversity but did not influence phylogenetic diversity. Taxonomic, but not phylogenetic, diversity generally was lower in older restorations and those with a longer time since the last prescribed fire. These drivers consistently explained more variation in taxonomic than phylogenetic diversity and composition, perhaps in part because species turnover was largely among related species, producing weak impacts on phylogenetic community measures.An impact of precipitation on taxonomic but not phylogenetic diversity suggests that there may not be large differences in drought tolerance among clades that would cause phylogenetic patterns to arise from this environmental filter. Declining taxonomic diversity but not phylogenetic diversity is consistent with competitive exclusion as an assembly mechanism when competition is strongest between related species.Synthesis. This research shows how studying taxonomic and phylogenetic diversity of ecosystem restorations can inform plant community ecology and help natural resource managers better predict the outcomes of restoration actions and management. 

Abstract Anthropogenic environmental changes are known to affect the Earth's ecosystems. However, how these changes influence assembly trajectories of the impacted communities remains a largely open question.In this study, we investigated the effect of elevated nitrogen (N) deposition and increased precipitation on plant taxonomic and phylogenetic β‐diversity in a 9‐year field experiment in the temperate semi‐arid steppe of Inner Mongolia, China.We found that both N and water addition significantly increased taxonomic β‐diversity, whereas N, not water, addition significantly increased phylogenetic β‐diversity. After the differences in local species diversity were controlled using null models, the standard effect size of taxonomic β‐diversity still increased with both N and water addition, whereas water, not N, addition, significantly reduced the standard effect size of phylogenetic β‐diversity. The increased phylogenetic convergence observed in the water addition treatment was associated with colonizing species in each water addition plot being more closely related to species in other replicate plots of the same treatment. Species colonization in this treatment was found to be trait‐based, with leaf nitrogen concentration being the key functional trait.Synthesis.Our analyses demonstrate that anthropogenic environmental changes may affect the assembly trajectories of plant communities at both taxonomic and phylogenetic scales. Our results also suggest that while stochastic processes may cause communities to diverge in species composition, deterministic process could still drive communities to converge in phylogenetic community structure.