Dry-wet seasonal variations of microbially mediated carbon metabolism in soils of a floodplain lake

Seasonal water level fluctuations in floodplain lakes are known to alter carbon transport, yet it is unclear how such changes affect microbially mediated carbon metabolism. Poyang Lake is a typical floodplain lake linked to the Yangtze River and is significantly affected by water level fluctuations. In this study, we examined the differences of soil organic matter (SOM) properties, bacterial communities and carbon metabolic functions between dry (March) and wet (August) seasons in lake centre, delta and floodplain from Poyang Lake. Generally, the SOM properties (quantity and quality) and microbially mediated carbon metabolism in the three types of sampling areas have undergone greater changes from dry to wet season than bacterial community. Structural equation modelling and variation partition analysis indicated that SOM properties contributed more in shaping the carbon metabolism of microorganisms than bacterial community structures, especially in lake centre. Dry-wet seasonal changes of microbially mediated carbon metabolism in lake centre were mainly affected by amide C=O-1650 and aliphatic C-H-2850,H- 2924, while the delta and floodplain were mainly affected by aromatic C-O-1234. Furthermore, we also found that bacterial community composition could better explain the effects of seasonal hydrology on carbon metabolism, rather than the diversity and assembly processes. We highlight that studies on tightly coupled changes in SOM and microbially mediated carbon metabolism can enhance the understanding of soil carbon dynamics across the floodplain lake.