Microbial carbon and phosphorus metabolism regulated by C:N:P stoichiometry stimulates organic carbon accumulation in agricultural soils

Soil organic carbon (SOC) is a key component of the carbon (C) cycle, and its accumulation is influenced by the stoichiometry of C: nitrogen (N): phosphorus (P), as well as microbial metabolism. However, the mechanisms driving SOC accumulation in agricultural and natural soils remain unclear. Therefore, this study aimed to investigate the impact of soil and microbial biomass (MB) C:N:P stoichiometry and microbial metabolic limitation on SOC accumulation in agricultural and natural soils. A survey of soils from 277 locations in eastern China was conducted, revealing that agricultural soils (paddy and upland soils) had 1.74-times higher SOC content than that of natural soils (wasteland and woodland soils). SOC showed a significant positive correlation with microbial C use efficiency (CUE), which in turn promoted SOC accumulation in agricultural soils. CUE was higher in agricultural soils (0.38-0.41) than in natural soils (0.25-0.31), which was attributed to reduced microbial metabolic limitation in agricultural soils. Increased nutrient supply was evident in agricultural soils, indicated by high SOC:TP, dissolved organic C:dissolved organic N, MBC:MBN, and MBC:MBP ratios, which alleviated microbial C and P limitations. However, in natural soils, low nutrient availability and enzyme activities resulted in significant microbial C and P limitations, thereby hindering SOC accumulation. Our results indicate that microbial metabolic limitation regulated by C:N:P stoichiometry stimulates SOC accumulation in agricultural soils, offering novel insights into SOC storage and emphasizing the importance of ecological stoichiometry and microbial metabolic limitation in SOC storage.