Shifts in the vegetation and microbial conditions accelerate soil organic carbon accumulation over a 65-year desert revegetation chronosequence

Revegetation in drylands is not only an effective strategy for curbing and reversing land desertification but also an effective approach to mitigating global climate change due to its significant organic carbon (OC) sequestration potential. Despite considerable progress in enhancing soil organic carbon (SOC) through revegetation, the long-term stability of carbon storage in drylands and the mechanisms underlying OC stabilization remain unclear. Here, we used a 65-year revegetation chronosequence in the Tengger Desert and applied sequential chemical extraction to separate SOC into functionally distinct OC fractions. SOC content increased from 0.63 g/kg at 11 years to 7.9 g/kg at 65 years, with a marked acceleration after 34 years. This 34-year threshold was identified by segmented function and signals a shift in both accumulation rate and carbon fraction composition. Extractable OC fractions (e.g., weakly adsorbed OC, metal–OC complexes, carbonate–OC, Fe-oxyhydroxide-OC–OC) rose sharply from 1.8 g/kg at 34 years to 3.9 g/kg at 48 years, then plateaued. In contrast, residual OC increased steadily from 0.6 g/kg to 5.9 g/kg between 34 and 65 years, becoming dominant. The relative contribution of extractable OC to SOC declined from 84 % to 47 %, while residual OC increased from 16 % to 53 %. Microbial biomass (phospholipid fatty acids, PLFAs) and community composition (fungi-to-bacteria ratio) were strongly associated with extractable OC fractions. In contrast, residual OC was primarily influenced by plant attributes (herb cover, litter biomass) and biocrust cover. These findings indicate that distinct biotic and abiotic factors regulate different OC fractions, leading to divergent responses under long-term revegetation. Overall, long-term revegetation in drylands accelerates SOC accumulation and promotes the formation of more stable carbon pools, contributing to enhanced soil resilience and climate change mitigation.