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Nutrient enrichment impacts grassland plant diversity such as species richness, functional trait composition and diversity, but whether and how these changes affect ecosystem stability in the face of increasing climate extremes remains largely unknown.We quantified the direct and diversity-mediated effects of nutrient addition (by nitrogen, phosphorus, and potassium) on the stability of above-ground biomass production in 10 long-term grassland experimental sites. We measured five facets of stability as the temporal invariability, resistance during and recovery after extreme dry and wet growing seasons.Leaf traits (leaf carbon, nitrogen, phosphorus, potassium, and specific leaf area) were measured under ambient and nutrient addition conditions in the field and were used to construct the leaf economic spectrum (LES). We calculated functional trait composition and diversity of LES and of single leaf traits. We quantified the contribution of intraspecific trait shifts and species replacement to change in functional trait composition as responses to nutrient addition and its implications for ecosystem stability.Nutrient addition decreased functional trait diversity and drove grassland communities to the faster end of the LES primarily through intraspecific trait shifts, suggesting that intraspecific trait shifts should be included for accurately predicting ecosystem stability. Moreover, the change in functional trait diversity of the LES in turn influenced different facets of stability. That said, these diversity-mediated effects were overall weak and/or overwhelmed by the direct effects of nutrient addition on stability. As a result, nutrient addition did not strongly impact any of the stability facets. These results were generally consistent using individual leaf traits but the dominant pathways differed. Importantly, major influencing pathways differed using average trait values extracted from global trait databases (e.g. TRY).Synthesis. Investigating changes in multi

Nutrient enrichment impacts grassland plant diversity such as species richness, functional trait composition and diversity, but whether and how these changes affect ecosystem stability in the face of increasing climate extremes remains largely unknown.We quantified the direct and diversity-mediated effects of nutrient addition (by nitrogen, phosphorus, and potassium) on the stability of above-ground biomass production in 10 long-term grassland experimental sites. We measured five facets of stability as the temporal invariability, resistance during and recovery after extreme dry and wet growing seasons.Leaf traits (leaf carbon, nitrogen, phosphorus, potassium, and specific leaf area) were measured under ambient and nutrient addition conditions in the field and were used to construct the leaf economic spectrum (LES). We calculated functional trait composition and diversity of LES and of single leaf traits. We quantified the contribution of intraspecific trait shifts and species replacement to change in functional trait composition as responses to nutrient addition and its implications for ecosystem stability.Nutrient addition decreased functional trait diversity and drove grassland communities to the faster end of the LES primarily through intraspecific trait shifts, suggesting that intraspecific trait shifts should be included for accurately predicting ecosystem stability. Moreover, the change in functional trait diversity of the LES in turn influenced different facets of stability. That said, these diversity-mediated effects were overall weak and/or overwhelmed by the direct effects of nutrient addition on stability. As a result, nutrient addition did not strongly impact any of the stability facets. These results were generally consistent using individual leaf traits but the dominant pathways differed. Importantly, major influencing pathways differed using average trait values extracted from global trait databases (e.g. TRY).Synthesis. Investigating changes in multi

Environmental factors, such as temperature, precipitation, and elevation, explain most of the variation in species richness at the global scale. Nevertheless, richness patterns may have different drivers across taxa and regions. To date, a comprehensive global examination of how various factors such as climate or topography drive patterns of species richness across all terrestrial vertebrates, using the same methods and predictors, has been lacking. Recent advances in species-distribution data allowed us to model and examine the richness pattern of all terrestrial tetrapods comprehensively. We tested the relationship between environmental and biogeographical variables and richness of amphibians (5983 species), birds (9630), mammals (5004), reptiles (8939), and tetrapods as a whole, globally, and across biogeographical realms. We studied the effects of climatic, ecological, and biogeographic drivers using generalized additive models. Richness patterns and their environmental associations varied among taxa and realms. Overall precipitation was the predominant richness predictor. However, temperature was more important in realms where both cold and warm conditions exist. In the Indomalayan realm, elevational range was very important. Richness patterns of mammals, birds, and amphibians were strongly related to precipitation whereas reptile richness was mostly associated with temperature. Our results support the universal importance of precipitation but also suggest that future global-scaled research should incorporate other relevant variables other than climate, such as elevational range, to gain a better understanding of the richness–environment relationship. By doing so, we can further advance our knowledge of the complex relationships between biodiversity and the environment.

Eutrophication impacts grassland diversity such as species richness, functional trait diversity and composition, but whether and how these changes affect ecosystem functional stability under increasing climate extremes is unknown. We quantify the direct and diversity-mediated effects of nutrient addition on functional stability of productivity as measured by resistance during and recovery after dry and wet growing seasons, and temporal invariability across 19 grasslands spanning four continents. We use leaf traits measured in the field to construct slow-fast leaf economic spectrum and calculate functional trait composition and diversity of the slow-fast trait. Nutrient addition increased resistance during dry growing seasons mainly through its direct effects. It also increased resistance during wet growing seasons directly, but these positive effects were weakened by indirect negative effects through reducing slow-fast functional diversity. Nutrient addition had weak effects on recovery after dry growing seasons, but it decreased recovery after wet growing seasons mainly through its direct effects. Nutrient addition increased temporal invariability through resistance, but decreased it through recovery and reducing species richness, leading to overall weak net effects. Thus, processes and influencing pathways independent of plant diversity should be carefully taken into account in understanding ecosystem stability in response to increasing global changes.

Anthropogenic nutrient enrichment and shifts in herbivory can lead to dramatic changes in the composition and diversity of aboveground plant communities. In turn, this can alter seed banks in the soil, which are cryptic reservoirs of plant diversity. Here, we use data from seven Nutrient Network grassland sites on four continents, encompassing a range of climatic and environmental conditions, to test the joint effects of fertilization and aboveground mammalian herbivory on seed banks and on the similarity between aboveground plant communities and seed banks. We find that fertilization decreases plant species richness and diversity in seed banks, and homogenizes composition between aboveground and seed bank communities. Fertilization increases seed bank abundance especially in the presence of herbivores, while this effect is smaller in the absence of herbivores. Our findings highlight that nutrient enrichment can weaken a diversity maintaining mechanism in grasslands, and that herbivory needs to be considered when assessing nutrient enrichment effects on seed bank abundance.

Anthropogenic nutrient enrichment and shifts in herbivory can lead to dramatic changes in the composition and diversity of aboveground plant communities. In turn, this can alter seed banks in the soil, which are cryptic reservoirs of plant diversity. Here, we use data from seven Nutrient Network grassland sites on four continents, encompassing a range of climatic and environmental conditions, to test the joint effects of fertilization and aboveground mammalian herbivory on seed banks and on the similarity between aboveground plant communities and seed banks. We find that fertilization decreases plant species richness and diversity in seed banks, and homogenizes composition between aboveground and seed bank communities. Fertilization increases seed bank abundance especially in the presence of herbivores, while this effect is smaller in the absence of herbivores. Our findings highlight that nutrient enrichment can weaken a diversity maintaining mechanism in grasslands, and that herbivory needs to be considered when assessing nutrient enrichment effects on seed bank abundance.