Aggregate-associated organic carbon regulates soil organic carbon during conversion from natural forest to Moso bamboo plantations and subsequent regeneration

Forest conversion and management cessation can alter soil organic carbon (SOC) through changes in aggregates, minerals, and microbes, but it remains unclear how these factors jointly regulate SOC recovery and whether this process is mediated by aggregate-associated organic carbon (AOC) and the resulting changes in particulate and mineral-associated organic carbon (POC and MAOC). Using a space-for-time analysis method, we compared four forest types; namely, natural evergreen broad-leaved forests (NF), managed Moso bamboo ( Phyllostachys edulis ) plantations (MB), and Moso bamboo plantations undergoing 5–7 and 15–17 years of natural regeneration after cessation of management (short-term (RBI) and medium-term (RBII), respectively). We quantified aggregate distribution, AOC, mineral properties, and microbial traits to assess their contributions to SOC stocks and fractions. Results indicated that forest conversion reduced SOC stocks by 64.96% and markedly decreased POC and MAOC concentrations, whereas management cessation increased aggregate stability and AOC and raised SOC stocks by 40.31% in RBII relative to MB. Aggregates, minerals, and microbial variables jointly explained 88.69% of SOC variance. Partial least squares path modeling analysis showed that AOC was closely associated with changes in POC and MAOC, which were in turn related to SOC stock recovery. These findings indicate that SOC dynamics are closely associated with AOC, which links aggregate, mineral, and microbial processes to carbon stabilization. Overall, our results highlight carbon sequestration processes during forest conversion and subsequent natural regeneration, providing insights for bamboo forest management and carbon sink assessment. • Examines the complete ecological process of the conversion of natural forests to managed Moso bamboo plantations and their subsequent natural regeneration after management cessation. • Quantifies the interactive roles of physical aggregate protection, mineral chemical stabilization, and microbial processes in SOC accumulation dynamics. • Forest management implementation accelerated carbon loss, while its cessation enhanced SOC recovery through improved aggregate stability and mineral-organic associations. • Aggregate-associated organic carbon is a key internal factor regulating SOC fractions and stocks.