Soil nitrogen mineralisation (N_min), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net N_min) varies with soil properties and climate. However, because most global-scale assessments of net N_minare laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net N_minacross 30 grasslands worldwide. We find that realised N_minis largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential N_minonly weakly correlates with realised N_min, but contributes to explain realised net N_minwhen combined with soil and climatic variables. We provide novel insights of global realised soil net N_minand show that potential soil net N_mindata available in the literature could be parameterised with soil and climate data to better predict realised N_min.

Significance: Predicting the effects of anthropogenic nutrient enrichment on plant communities is critical for managing implications for biodiversity and ecosystem services. Plant functional types that fix atmospheric nitrogen (e.g., legumes) may be at particular risk of nutrient-driven global decline, yet global-scale evidence is lacking. Using an experiment in 45 grasslands across six continents, we showed that legume cover, richness, and biomass declined substantially with nitrogen additions. Although legumes benefited from phosphorus, potassium, and other nutrients, these nutrients did not ameliorate nitrogen-induced legume decline. Given global trends in anthropogenic nutrient enrichment, our results indicate the potential for global decline in grassland legumes, with likely consequences for biodiversity, food webs, soil health, and genetic improvement of protein-rich plant species for food production.