Rhizosphere soil C:P stoichiometry differentially regulates microbial necromass carbon responses to nitrogen and phosphorus addition in subtropical forests

Subtropical forest soils are typically nitrogen (N)-rich but phosphorus (P)-deficient, creating a strong stoichiometric imbalance that may reshape microbial pathways responsible for soil organic carbon (SOC) stabilization, particularly in the microbially active rhizosphere. Microbial necromass carbon (MNC) is a stable component of SOC, but the mechanisms by which microbial traits (e.g., functional diversity, life-history strategies, and network interactions) regulate MNC accumulation under N and P addition remain unclear. This study conducted N and P addition experiments in a subtropical forest, and collected rhizosphere soil from four representative broadleaf tree species, to assess the microbial mechanisms and pathways driving MNC variation in response to soil ecological stoichiometry. The results showed that N addition significantly increased FNC and MNC, whereas P addition significantly reduced both; BNC increased under both treatments. The rhizosphere soil C:P ratio was strongly associated with MNC variation, and it increased markedly under N addition while it decreased under P addition. Furthermore, variation in FNC was closely associated with microbial r-strategists, r/K ratios, and network degree, whereas variation in BNC was linked to microbial functional diversity and network degree. These findings demonstrate that rhizosphere soil C:P stoichiometry integrates nutrient availability, microbial community traits, and network interactions to regulate MNC accumulation. By revealing how N and P addition shift this balance in the rhizosphere soil, our study provides mechanistic insights with broader implications for understanding microbial contributions to long-term SOC stabilization in forest ecosystems.