Abstract: The active components of soil organic carbon are sensitive indicators of carbon stock change, which can timely reflect the turnover and dynamics of soil organic carbon pool. In this study, soil samples at 0-10 cm (surface layer), 10-30 cm (middle layer) and 30-60 cm (deep layer) depths of four typical plant communities were collected in Yancheng coastal wetlands. The relationships between soil total organic carbon (TOC), easily oxidizable carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC) and soil environmental factors and aboveground biomass (AGB) were examined. The results showed that: (1) TOC content varied greatly in different plant communities, whereas the differences in soil EOC and DOC contents were relatively minor. TOC content declined with soil depths except for the Spartina alternifloracommunity, which was slightly higher in deep layers. POC content gradually decreased with soil depths. (2) Redundancy analysis results showed that AGB and soil pH had the highest single explanatory power for the variation of soil organic carbon component content in the three soil layers. With increasing soil depth, the explanatory power of total reducing substances (RS) showed an upward trend. The separate explanatory power of soil water content (SWC) in surface and middle layers was the lowest. Soil water content had little effect on the content of soil organic carbon components. (3) EOC was significantly positively correlated with total phosphorus (TP) and total nitrogen (TN), negatively correlated with pH in surface layer, and had no correlation with soil factors in the middle and deep layers. DOC was significantly positively correlated with AGB, TP, and RS in surface layer, positively correlated with TN, TP and SWC in the middle layer, and negatively correlated with pH in deep layer. POC was significantly positively correlated with AGB, TP and RS in surface and middle layers, but not in the deep layer. Our results indicated that AGB and soil pH significantly affected the contents of soil organic carbon components in the three soil layers, while the effect of soil redox status was more significant with the increasing soil depths. The relative contents of soil organic carbon components and their influencing factors were quite different, depending on community types, soil layers, and organic carbon component types.

Key words: coastal wetland, soil factor, easily oxidizable carbon, dissolved organic carbon.