Rice straw returning under winter green manuring enhances soil carbon pool via stoichiometric regulation of extracellular enzymes

The combined application of green manure and rice straw (GMS) effectively enhances carbon sequestration in paddy fields. However, the regulatory mechanisms governing straw carbon incorporation into soil organic carbon (SOC) pools under this practice remain unclear. A two-year study was conducted based on a long-term field experiment to investigate soil organic carbon storage, decomposition patterns of rice straw (S) and green manure (GM), extracellular enzyme stoichiometry, and carbon flux dynamics between straw and soil pools. Over seven years, GMS exhibited annual carbon sequestration rates surpassing those of GM, S, and winter fallow without S return (CF) by 518, 451, and 766 kg/ha/year, respectively. Regulated by nutrient stoichiometry, extracellular enzyme activities associated with residue decomposition and carbon limitation of microbial metabolism were enhanced in GMS, thereby accelerating decomposition processes. Following the two-year experimental period, decomposition rates in GMS were elevated by 23.4 % and 32.7 % relative to GM and S treatments, respectively. This accelerated decomposition promoted the translocation of straw carbon into stable SOC pools via microbial residue pathways, as substantiated by 54.2 %, 25.5 %, and 18.4 % greater amino sugar accumulation in GMS relative to CF, GM, and S treatments, respectively. In summary, GMS regulates microbial resource allocation through stoichiometric modulation of residues, functioning as a critical interface governing straw carbon transfer to SOC pools, thus ultimately enhancing SOC sequestration.