Microbes drive global soil nitrogen mineralization and availability

Soil net nitrogen mineralization rate (N min ), which is critical for soil nitrogen availability and plant growth, is thought to be primarily controlled by climate and soil physical and/or chemical properties. However, the role of microbes on regulating soil N min has not been evaluated on the global scale. By compiling 1565 observational data points of potential net N min from 198 published studies across terrestrial ecosystems, we found that N min significantly increased with soil microbial biomass, total nitrogen, and mean annual precipitation, but decreased with soil pH. The variation of N min was ascribed predominantly to soil microbial biomass on global and biome scales. Mean annual precipitation, soil pH, and total soil nitrogen significantly influenced N min through soil microbes. The structural equation models ( SEM ) showed that soil substrates were the main factors controlling N min when microbial biomass was excluded. Microbe became the primary driver when it was included in SEM analysis. SEM with soil microbial biomass improved the N min prediction by 19% in comparison with that devoid of soil microbial biomass. The changes in N min contributed the most to global soil NH 4 + ‐N variations in contrast to climate and soil properties. This study reveals the complex interactions of climate, soil properties, and microbes on N min and highlights the importance of soil microbial biomass in determining N min and nitrogen availability across the globe. The findings necessitate accurate representation of microbes in Earth system models to better predict nitrogen cycle under global change.