Crop residue returning represents a pivotal agricultural practice for replenishing soil organic carbon (SOC), which constitutes the largest active carbon pool in terrestrial ecosystems. To explore the microbial mechanisms driving the dynamic decoupling between SOC accumulation and stability, we conducted a 98-day decomposition experiment using acidic red soil and high C:N ratio Italian ryegrass crop residues. Crop residue decomposition significantly increased SOC contents by 14.76–41.33%. The contents of SOC, microbial biomass carbon, and easily oxidized organic carbon, as well as the related enzyme activities, initially increased before decreasing as decomposition progressed, peaking around 28 or 42 days. Concurrently, SOC chemical stability initially decreased, then stabilized, as indicated by the dynamics of the Alkyl C/O-alkyl C ratio and hydrophobicity. The early-stage SOC accumulation was closely associated with the rapid proliferation of specific r-strategy taxa and the increased relative abundances of glycoside hydrolase genes. Subsequently, the recovery of SOC stability coincides with a shift toward K-strategy microorganisms and increased relative abundances of auxiliary active genes. This highlights a microbial-mediated dynamic decoupling between SOC content and stability, driven by the succession of microbial CAZymes gene profiles. The shift in microbial life-history strategies (from r-strategy microorganisms to K-strategy microorganisms) and their associated enzymatic machinery could collectively facilitate the efficient utilization of root-derived carbon. Our findings reveal the microbial-mediated dynamic decoupling between SOC accumulation and stability during crop residue decomposition, which advances our understanding of how residue inputs contribute to soil carbon sequestration.
Cao et al. (Mon,) studied this question.