Global nitrogen enrichment impacts plant diversity more than soil bacterial and fungal diversity: a meta-analysis

Anthropogenic nitrogen enrichment has significant effects on plant and soil biodiversity across local to global scales, yet how the nitrogen-induced changes in plant diversity differ from those in soil organisms across multiple ecosystems and climatic conditions remains virtually unknown. By synthesizing plant and soil studies globally (3,816 paired observations from 458 articles), we demonstrate that nitrogen enrichment has stronger negative effects on plant diversity but surprisingly modest to negligible effects on soil bacterial and fungal diversity. On average, nitrogen enrichment results in 8.3% and 10.3% reductions in species richness and Shannon index for plants. In contrast, it leads to 1.9% and 0.2% reductions for soil bacteria and <0.4% changes for soil fungi, respectively. The nitrogen-induced soil acidification modulates soil biodiversity change and, in conjunction with aboveground biomass, regulates plant biodiversity change. Our findings provide a perspective on the differential impacts of global nitrogen enrichment on above- and below-ground biodiversity, highlighting the need for integrated biodiversity conservation strategies.