Abstract: Soil labile organic carbon is sensitive to environmental changes. We investigated the contents of labile organic carbon fractions in different types of wetland soils and its influencing factors in Yili Valley, including the longterm flooding reed (Phragmites australis) wetland, rarely flooding ditch millet (Paspalum orbiculare) wetland, and seasonal flooding chee reedgrass (Calamagrostis epigeios) wetland. The concentrations of easily oxidized organic carbon (EOC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) in 0-40 cm soil layers of different types of wetlands were measured. The correlations between soil EOC, DOC and MBC, and their relationships with activities of soil enzymes (invertase, urease, catalase), soil nutrient concentrations (ammonium nitrogen, total phosphorus) and soil organic carbon (SOC) concentrations were analyzed. The vertical differentiation of the soil labile organic carbon contents in the 0-40 cm soil layer in the three different types of wetland was consistent, decreasing with soil depth across the soil profile. The contents of MBC, EOC and DOC were significantly different among the three wetlands (P<0.05), with lowest contents of MBC, EOC and DOC in reed wetland. Among the three types of wetlands, the proportions of MBC, EOC and DOC in SOC were 4.33%-18.02%, 28.85%-66.06%, and 0.73%-1.36% in the 0-40 cm soil layer, respectively. There was no consistent pattern of the proportions of MBC and EOC, except that the proportion of DOC in SOC increased first and then decreased. Among the three soil labile organic carbon fractions, the proportion of the EOC was the highest and that of the DOC was the lowest. The highest proportions of MBC and EOC in SOC were found in the ditch millet wetland. The highest proportion of DOC was found in the chee reedgrass wetland. The proportions of MBC, EOC and DOC in reed wetlands were relatively lower. The correlations between the MBC, EOC and DOC in the three types of wetlands were significantly correlated. The correlation between DOC and soil total phosphorus was not significant, while the three soil labile organic carbon fractions with soil nutrients and soil enzyme activities were significantly correlated. Our results indicated that soil enzyme activities and soil nutrients were important factors affecting soil labile organic carbon contents.

Key words: Wanshan District, Zhuhai, marine ecosystem service, emergy value, monetary value.