Effects of the conversion of croplands to wetlands on the components and sources of soil organic carbon

Land use/cover change (LUCC) plays an important role in soil organic carbon (SOC) storage. However, the responses of SOC components to LUCC and the contribution of microbial-derived carbon (typically represented by microbial necromass carbon, MNC) to SOC in wetland-related LUCC remain unclear. In this study, we investigated the responses of SOC components and the contribution of microbial-derived carbon to SOC in three newly formed wetlands that were converted from croplands by coal mining subsidence and have developed for 1, 6, and 15 years, respectively. The findings revealed that the conversion initially led to the decrease of SOC, and then recovered with time, in which occluded particulate organic carbon (oPOC) dominated the response of SOC to the conversion and significantly accumulated in the wetland with 15 years of development. Moreover, our study found that MNC accounted for a minor fraction (5.9 %–13.1 %) of SOC in the newly formed wetlands, which is contrary to the dominant role of MNC in the contribution to SOC in upland soils. Our study provides evidence for understanding the role of microbial-derived carbon in newly formed wetlands and highlights the importance of oPOC when focusing on the effects of LUCC on SOC storage.