Abstract: Soil labile organic carbon (LOC), a group of dynamic chemical compounds, is important in global carbon (C) cycling due to its short turnover time and sensitivity to environmental changes. However, variation of LOC along elevational gradients in subtropical forests is not fully understood. In this study, we investigated LOC groups, i.e. microbial available carbon (MAC), microbial biomass carbon (MBC), easily oxidation carbon (EOC), water-soluble organic carbon (WSOC), light fraction carbon (LFC) in three soil layers (0–10, 10–25 and 25–40 cm) in different communities along an elevation gradient in the Wuyi Mountains in southeastern China. We also examined plant litter mass (LM), soil temperature and moisture in three soil layers in all communities. We found that MAC, MBC, EOC and WSOC content increased along the elevation gradient across all soil depths, whereas LFC was higher in communities with low elevations compared to others across all soil depths. Soil temperature and moisture mainly regulated MAC, MBC, EOC and WSOC, and plant litter controlled LFC. Positive correlations were found among soil organic carbon (SOC) pools (MAC, MBC, EOC, WSOC, and SOC) (P<0.001) across communities, except for LFC.  LFC was positively correlated to other pools at low elevations and high elevations, respectively. Overall, LOC pools decreased with increasing soil depth across communities. Our results suggest that LOC content principally dependeds on the amount of SOC and LOC groups are good indicators for predicting minor changes of SOC in the C cycle.

Key words: soil organic carbon, labile organic carbon;, fractionation methods, soil depth, elevational gradient (vegetations)