Effects of hydrological environment on litter carbon input into the surface soil organic carbon pool in the Dongting Lake floodplain

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Litter carbon is the main source of the surface soil organic carbon pool (S-SOCP). However, the impact of changes in the hydrological environment of natural wetlands on litter input to S-SOCP remains unclear. In the present study, the effects of hydrological changes (soil water content [SWC] and days of flooding [DF]) on the litter decomposition process and S-SOCP were investigated from January 2018 to November 2019 in the Dongting Lake floodplain of China. Furthermore, the contribution of litter to the S-SOCP in Carex meadow and Reed wetland were calculated. The results showed that a large part of litter (approximately 50%–70%) decomposed annually, especially during the flooding season. Litter contributed 283.68 g C m−2 a–1 to the S-SOCP in the Carex meadow and 275.24 g C m−2 a–1 to the Reed wetland. In the Carex meadow and Reed wetland, the belowground litter contribution was higher than the aboveground litter during the non-flooding season. In contrast, during the flooding season, the aboveground litter contribution in the Carex meadow is higher, whereas the belowground litter dominates in the Reed wetland. The SWC indicated a positive correlation with soil organic carbon (SOC) and a negative correlation with the microbial biomass carbon (MBC) and dissolved organic carbon (DOC) in the Carex meadow. However, SWC shows a negative correlation with SOC and a positive correlation with MBC in the Reed wetland during the non-flooding season. During the flooding season, the variation of DOC during the flooding season (ΔDOC) is positively correlated with DF in the Carex meadow and Reed wetland. SWC and DF are the main drivers of litter decomposition into the S-SOCP in non-flooding and flooding seasons, respectively. Therefore, the construction of microhabitat with prolonged flooding and relatively higher soil water content are essential ways to improve the carbon sequestration potential in floodplains.