Abstract: The effect of land use change on soil organic carbon (SOC) is a major research context of global carbon cycling. SOC content and its fractions were determined from soils collected from three land use types including mangrove wetland (WS), dry land (converted from wetland, DS) and paddy soil (PS) in Zhangjiangkou, Fujian, China. Results showed that SOC content in WS soil was significantly higher than that in DS (by 29.50%) and PS (19.56%). Conversion of WS to DS increased the contents of dissolved organic carbon (DOC), microbial biomass carbon (MBC) and mineralassociated organic carbon (MOC) significantly by 40.39%, 248.43% and 144.00% respectively, while decreased the contents of heavy fraction organic carbon (HFOC), light fraction organic carbon (LFOC) and coarse particulate organic carbon (CPOC) contents by 20.91%, 46.44%, 36.58%, respectively. The content of all SOC fractions in PS were higher than in DS, but lower than in WS, except MBC, FPOC and MOC. Pearson correlation showed that SOC content significantly correlated to HFOC, LFOC, CPOC and MOC contents. These findings suggest that the conversion of mangrove wetland to dry land might trigger the loss of SOC, while soil C content could be increased by reasonable management.

Key words: Tibetan Plateau, precipitation concentration index, precipitation change, precipitation centroid, NDVI maximum.