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Abstract Global environmental change is causing a decline in biodiversity with profound implications for ecosystem functioning and stability. It remains unclear how global change factors interact to influence the effects of biodiversity on ecosystem functioning and stability. Here, using data from a 24-year experiment, we investigate the impacts of nitrogen (N) addition, enriched CO₂(eCO₂), and their interactions on the biodiversity-ecosystem functioning relationship (complementarity effects and selection effects), the biodiversity-ecosystem stability relationship (species asynchrony and species stability), and their connections. We show that biodiversity remains positively related to both ecosystem productivity (functioning) and its stability under N addition and eCO₂. However, the combination of N addition and eCO₂diminishes the effects of biodiversity on complementarity and selection effects. In contrast, N addition and eCO₂do not alter the relationship between biodiversity and either species asynchrony or species stability. Under ambient conditions, both complementarity and selection effects are negatively related to species asynchrony, but neither are related to species stability; these links persist under N addition and eCO₂. Our study offers insights into the underlying processes that sustain functioning and stability of biodiverse ecosystems in the face of global change. 

ABSTRACT AimGlobal climate change is compressing species' realised niches and further threatening their distributions. Species traits, especially the trait spectra synthesised from traits, are one way in which species can match changes in their environment. Hence, integrating trait spectra and niches will help us understand how species adapt to their environment under global change. LocationGlobal. Time PeriodPresent. Major Taxa StudiedAngiosperms. MethodWe collected root traits from 158 angiosperm species and leaf traits from 512 angiosperm species from a global trait database to construct the leaf and root trait ‘slow‐fast’ spectrum based on resource acquisition strategy, as well as the collaboration spectrum related to root mycorrhizal colonisation. After rebuilding their phylogenetic relationships and defining species' environmental niches based on 213,979 occurrences of these species, we examined the relationship between these trait spectra and environmental niches along global climatic patterns. ResultPlants with ‘slow’ leaf traits were generally associated with narrow niche breadths and marginal niche positions, especially in high precipitation areas. The relationship between the ‘slow‐fast’ spectrum in root traits and ‘marginal‐central’ niche position reversed with decreasing precipitation. However, the relationships between leaf traits and niche variables were significant for woody species but not for herbaceous species. Main ConclusionOur research expands the plant trait spectra in macroecology applications. The root and leaf ‘slow‐fast’ trait spectra of angiosperms are driven by both macroclimate and long‐term evolutionary pressure. Understanding how these traits relate to the niche of species helps to predict how that species is likely to adapt to environmental change, which can enhance the predictive ability of niche theory for plant environmental adaptability. 

Abstract Effects of plant diversity on grassland productivity, or overyielding, are found to be robust to nutrient enrichment. However, the impact of cumulative nitrogen (N) addition (total N added over time) on overyielding and its drivers are underexplored. Synthesizing data from 15 multi-year grassland biodiversity experiments with N addition, we found that N addition decreases complementarity effects and increases selection effects proportionately, resulting in no overall change in overyielding regardless of N addition rate. However, we observed a convex relationship between overyielding and cumulative N addition, driven by a shift from complementarity to selection effects. This shift suggests diminishing positive interactions and an increasing contribution of a few dominant species with increasing N accumulation. Recognizing the importance of cumulative N addition is vital for understanding its impacts on grassland overyielding, contributing essential insights for biodiversity conservation and ecosystem resilience in the face of increasing N deposition. 

Abstract Plant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e., higher species-level productivity in diverse communities compared with monocultures) remains unclear. Here, using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition either decreasing or increasing. In forests, temporal trends in species overyielding differ when considering above- versus belowground resource acquisition strategies. Overyielding in stem growth decreased for species with high light capture capacity but increased for those with high soil resource acquisition capacity. Our results imply that a diversity of species with different, and potentially complementary, ecological strategies is beneficial for maintaining community productivity over time in both grassland and forest ecosystems. 

Summary Humans are driving biodiversity change, which also alters community functional traits. However, how changes in the functional traits of the community alter ecosystem functions—especially belowground—remains an important gap in our understanding of the consequences of biodiversity change.We test hypotheses for how the root traits of the root economics space (composed of the collaboration and conservation gradients) are associated with proxies for ecosystem functioning across grassland and forest ecosystems in both observational and experimental datasets from 810 plant communities. First, we assessed whether community‐weighted means of the root economics space traits adhered to the same trade‐offs as species‐level root traits. Then, we examined the relationships between community‐weighted mean root traits and aboveground biomass production, root standing biomass, soil fauna biomass, soil microbial biomass, decomposition of standard and plot‐specific material, ammonification, nitrification, phosphatase activity, and drought resistance.We found evidence for a community collaboration gradient but not for a community conservation gradient. Yet, links between community root traits and ecosystem functions were more common than we expected, especially for aboveground biomass, microbial biomass, and decomposition.These findings suggest that changes in species composition, which alter root trait means, will in turn affect critical ecosystem functions.