Microbial necromass carbon drives soil organic carbon accumulation during long‐term vegetation succession

Abstract Plant‐ and microbial‐derived carbon (C) are the two major sources of soil organic carbon (SOC) pools that make important contributions to stable and labile SOC. Although the hypothesis of an increase in SOC during natural vegetation restoration has been broadly verified, the contributions of plant‐ and microbial‐derived C to SOC accumulation remain uncertain. In this study, we used biomarker approaches to assess the contribution and allocation of plant‐ and microbial‐derived C in long‐term vegetation succession sequences. We found a unimodal distribution of total lignin phenols along vegetation succession, with the maximum occurring at 100 years of succession (293 ± 22.7 mg kg −1 ). Vegetation succession significantly increased microbial‐derived C, including microbial necromass C (MNC) and glomalin‐related soil proteins (GRSP). The contribution of MNC to SOC was high (26%–49%) and increased significantly with vegetation succession, whereas the proportion of plant‐derived C and GRSP in SOC consistently decreased. The results indicated that the distribution of lignin phenols is determined by the quality and abundance of plant litter input to the soil, and the increase in microbial‐derived C is closely associated with microbial metabolism mediated by environmental factors. However, the C turnover pathway from microbial necromass to persistent SOC formation, as inferred from the nonlinear response of the MNC accumulation coefficient, requires 90–100 years to achieve a stable contribution to soil C sequestration. Synthesis and applications . Our findings further highlight the critical role of the microbial C pump in SOC formation and accumulation. We argue that prioritizing native pioneer species and their mixed communities with climax species during revegetation of extensive fragile ecosystems contributes to sustainable soil C sequestration practices.