Abstract: In this study the concentration and distribution of soil organic carbon (SOC), as well as the labile SOC in soil of three forest types including an evergreen-deciduous broad-leaved forest, a mixed broadleaf-coniferous forest and a subalpine dark coniferous forest were investigated in western Sichuan, China. Results indicated that SOC concentration in the surface soil (0-15cm) across three forest types was 44.21-179.98g·kg-1, with the highest value in the mixed broadleaf?coniferous forest, followed by the evergreen-deciduous broad-leaved forest, and then the coniferous forest. In all of the three forests the soil of 0-5cm layer relative to that of 5?15cm layer had a higher SOC concentration, indicating a surface gathering characteristic of SOC in the forests. The SOC density did not differ among the three forests, while significant differences in light of the vertical variation of SOC density along soil depth were detected among the three forests, where the mixed broadleaf-conifer forest compared to the other two forests had a higher SOC density in the 5?15cm soil depth. Although the concentrations of dissolved organic carbon (DOC), light fraction organic carbon (LFOC) and microbial biomass carbon (MBC) were highest in the mixed broadleaf-conifer forest, the coniferous forest among the three forests was highest in the ratios of these parameters to total SOC content, indicating a higher accumulation of labile SOC in forest with a higher elevation. The results suggest that ecosystem with a higher elevation may have a higher risk of CO2 emission under the circumstance of the climate warming.

Key words: Organic carbon content, Carbon storage, Microbial biomass carbon, Labile organic carbon