Mycorrhizal types and leaf habits co-regulate soil organic carbon in subtropical forests

Abstract Forest soil organic carbon (SOC) constitutes a critical component of the terrestrial carbon pool. While the two tree characteristics [arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM)] and the leaf habits (e.g. evergreen vs. deciduous) are known to significantly influence soil carbon cycling. The combined effects of mycorrhizal types and leaf habits on SOC accumulation in subtropical forests are poorly understood. To elucidate the relative importance of mycorrhizal types and leaf habits on SOC accumulation and its drivers, we sampled soil at four subtropical forests, representing distinct mycorrhizal-leaf habits combinations: evergreen ECM-associated, evergreen AM-associated, deciduous ECM-associated and deciduous AM-associated forests. Our results showed that both mycorrhizal types and leaf habits significantly influenced SOC accumulation. ECM-evergreen forests exhibited the highest SOC stocks, primarily driven by enhanced particulate organic carbon (POC) accumulation, together with elevated extracellular enzyme activities and a higher ratio of fungi to bacteria (F/B), consistent with a slow-decomposition strategy. In contrast, AM-associated and deciduous forests promoted a greater proportion of mineral-associated organic carbon (MAOC), reflecting faster microbial turnover and more efficient microbial–mineral stabilization. Leaf habits modulated mycorrhizal effects, attenuating differences between AM and ECM forests. Our work elucidated how mycorrhizal types and leaf habits co-shape SOC accumulation in subtropical forests, offering valuable scientific insights for species selection in forest management strategies focused on carbon accumulation.