Forest soil carbon pools constitute a vital component of terrestrial ecosystem carbon reser-voirs and play a significant role in long-term carbon sequestration.Although subtropical China,characterized by favorable hydrothermal conditions,supports extensive areas of planted forests,the for-mation mechanisms of soil organic carbon(SOC)in these ecosystems remain poorly understood.In this study,six subtropical monoculture plantations were selected to investigate the stock size,compositional characteristics,and key influencing factors of their organic carbon pools.The results showed that,1)the mean SOC content in the surface layer(0～10 cm)across the plantations was 33.94 g·kg-1,in which particulate organic carbon(POC mean 10.52 g·kg-1),and mineral-associated organic carbon(MAOC mean 23.42 g·kg-1)accounted for approximately 31.0%and 69.0%of total SOC,respec-tively.(2)MAOC exhibited a lower coefficient of variation(CV=15.38%)than POC(CV=18.22%).3)POC was positively correlated with root C/N ratio(P≤0.01)and litterfall mass(P≤0.05).4)MAOC was significantly positively correlated with total nitrogen and soil C/N ratio(P≤0.01),and the MAOC/SOC ratio shows a strong positive correlation with soil bulk density(P≤0.01).(5)Microbial biomass correlated significantly with MAOC(P≤0.05)but showed no correla-tion with POC.These findings indicate that MAOC,as the dominant component of SOC in the surface soils of subtropical plantations,is present in higher concentrations than POC,with both fractions ex-hibiting considerable variability.Specifically,the labile carbon pool(POC)is primarily regulated by plant carbon inputs(litterfall mass and root C/N ratio),whereas the stable carbon pool(MAOC)de-pends on the synergistic interactions between soil physicochemical properties(bulk density and nitrogen availability)and microbial processes.This study elucidates the compositional characteristics of SOC in subtropical plantations and provides a scientific basis for tree species selection in carbon-targe-ted plantation management.