Microbial Residues and Soil Organic Carbon Stability in Grasslands: Impacts of Exogenous Nitrogen Input

Elevated reactive nitrogen (N) inputs from fertilization and fossil fuel combustion increasingly threaten the soil carbon storage capacity of grassland ecosystems. However, the stability of soil organic carbon within these ecosystems is increasingly at risk. Recent research has highlighted the importance of microbial residues in regulating the stability of soil organic carbon. Despite this recognition, there is still a limited understanding of the impact of microbial residues on soil organic carbon stability in grasslands subjected to external nitrogen inputs, as well as the underlying regulatory mechanisms involved. This review aims to synthesize current knowledge on how nitrogen (N) addition and its duration regulate microbial residue accumulation and its contribution to SOC pools (particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)) in grassland ecosystems, with emphasis on the roles of microbial community composition, microbial biomass carbon, and enzyme activities. By integrating these perspectives, this review aims to advance understanding of the mechanisms governing microbial residue dynamics under nitrogen enrichment and to identify priorities for future research.