Soil Nitrogen Mineralization Is Driven by Functional Microbiomes Across a North-South Forest in China

Nitrogen (N) mineralization is a complex microbial-driven process that controls the supply of N for plants and microbes. The relative contribution of different microbial N-cycling species/genes to the variation in N mineralization rate (NMR) across contrasting forest biomes was unclear. Here, we investigate the linkages between soil metagenomes and N mineralization rates across 10 contrasting forest biomes (covering temperate, subtropical, and tropical forests) along a 3425 km north-south forest in China. We found that the NMR was higher in subtropical forests, and the variation in NMR can be explained by climate and soil environments, particularly for soil substrate NH₄⁺. Similar to NMR, microbial N-cycling genes/species were also higher in subtropical forests, suggesting that the higher microbial N-cycling traits in warm regions may drive higher NMR. We also quantified the contribution of microbial N-cycling gene pathways to NMR across forest biomes and found that the microbial N-denitrification pathway (genes like norZ, narG, nirK, and norB) and nitrification pathway (genes like nxr) explained more variation in NMR than other pathways, such as N ammonification. Collectively, our work demonstrates the importance of microbial N-cycling traits to explain soil N mineralization rates across forest biomes and suggests that this information can be used to help improve the management of the N cycle in forests across biomes.