Stoichiometry Influences on Microbial Necromass Carbon Contributions to Soil Organic Carbon in A Chinese Fir Plantation Under a 7‐Year Litter Manipulation

Abstract

Microbial necromass is microbial assimilation metabolites that are important for soil organic carbon (SOC) accumulation. Stoichiometric ratios reflect the relative abundances of various elements in forest ecosystems, and the proportions of carbon (C), nitrogen (N), and phosphorus (P) in an organism affect its metabolic capacity, biomass, and final necromass yield. However, the mechanism by which soil stoichiometry regulates microbial necromass is unclear. The effect of soil stoichiometry on microbial necromass was investigated using a 7‐year field manipulation experiment in a subtropical Chinese fir (Cunninghamia lanceolata) plantation with aboveground litter addition and removal. We measured microbial necromass C contributions to SOC (MNC/SOC) and the stoichiometric ratios of total and available nutrients, microbial biomass, and enzyme activities. MNC/SOC at the 0–10 cm soil layer was significantly increased by litter addition rather than litter removal. The stoichiometric ratios of available nutrients (31%) and enzymatic activities (15%) explained the variations in the MNC/SOC. The fungal MNC/SOC was positively correlated with the C/N ratios of microbial biomass and enzyme activities, whereas the bacterial MNC/SOC was only correlated with the C/P and N/P ratios of available nutrients and enzyme activities, which indicated that the relationship between fungal and bacterial MNC/SOC and stoichiometry ratios was not exactly the same. However, the MNC/SOC and stoichiometric ratios did not have significant correlations below the 20 cm soil layers, which indicated that the relationship was decoupled with increasing soil depth. Our results provide a holistic understanding of soil stoichiometry to elucidate the mechanisms of MNC accumulation and contribution along the soil profile in a subtropical forest, providing new insights and research directions for enhancing C sequestration and improving soil quality.