Nitrogen and phosphorus enrichment differentially affect grassland ecosystem functioning via multitrophic pathways

Abstract The enrichment of nutrients (e.g. N and P) is crucial in shaping the links between diversity and ecosystem functions. Previous research has mainly focused on how nutrient enrichment affects community diversity and composition within a single trophic level, such as plants or soil microbial communities. However, how nutrient enrichment affects community composition and diversity across multiple trophic levels and ecosystem functions has not been extensively explored. By conducting two long‐term N‐ and P‐enrichment experiments in temperate steppes, we explored the response of diversity and composition at both the community and functional group level across the soil food webs to nutrient enrichment, as well as their relationship with ecosystem functions. We found that the responses of soil biota and plants to nutrient enrichment varied depending on the community and functional group. N‐enrichment resulted in a decrease in plant and bacterial richness at both the community and functional group levels, while P‐enrichment decreased fungal and nematode richness at both levels. In addition, N‐enrichment changed the community composition of plants and all soil biota, while P‐enrichment only affected the community composition of fungi and nematodes. Our findings also showed that community composition across multiple trophic levels played a crucial role in regulating ecosystem functions (e.g. plant biomass, soil biota biomass and SOM decomposition) when considering both community composition and diversity simultaneously. For example, N‐enrichment induced changes in the community composition of plants, bacteria and nematodes, which altered plant biomass, while P‐enrichment induced changes in the community composition of nematodes that altered soil biota biomass and SOM decomposition. Synthesis . Overall, our study suggests that long‐term nutrient enrichment may have a greater impact on community composition than diversity across multiple trophic levels, and these changes in community composition can have broad implications for ecosystem functions. Therefore, more effort should be made not only on community diversity but also on composition to clarify the relationship between diversity and ecosystem functions in future studies under climate change.