Abstract: Soil organic carbon in forest affects nutrient availability, microbial processes, and organic matter inputs. Dominant tree species have increasingly shifted from ectomycorrhizal to arbuscular mycorrhizal associations in subtropical forests. However, the consequences of this shift for soil organic carbon is poorly understood. To address this, a field study was conducted across a natural gradient of arbuscular tree associations to investigate how different mycorrhizal associations affect soil organic carbon quantity, composition, chemical stability, and related soil properties. Soil organic carbon fractions, functional groups, microbial enzyme activities were analyzed. Results showed that increasing arbuscular mycorrhizal dominance was associated with declines in total soil organic carbon, particularly in recalcitrant and aromatic carbon forms. Ectomycorrhizal-dominated forests exhibited higher nitrogen availability and elevated nitrogen-hydrolyzing enzyme activity, suggesting enhanced nitrogen acquisition strategies that suppress soil organic carbon decomposition and promote carbon retention. These findings indicate that mycorrhizal-mediated shifts in tree composition may significantly alter soil carbon sequestration potential. Incorporating mycorrhizal functional traits into forest management and carbon modeling could improve predictions of soil organic carbon responses under future environmental change.

Key words: Arbuscular mycorrhizal trees, Ectomycorrhizal trees, Soil organic carbon pool, Nitrogen hydrolase activity