Differences in sediment carbon-fixation rate and associated bacterial communities in four wetland types in Hulun Lake Basin

CO2 assimilation by autotrophic microbes in wetland sediments has substantial significance in global warming control. However, among wetland types in the lake basin, the differences in the carbon sequestration processes undertaken by autotrophic microorganisms remain unclear. We aimed to investigate these differences and compared the sediment CO2-fixation rates (CFRs) and the cbbL- and coxL-containing microbial communities in swamp, lake, and river wetlands in summer and autumn in Hulun Lake Basin, China, besides exploring the difference mechanism by considering the sediment physicochemical properties. We found that microbial CFRs and associated microbial communities varied significantly among wetland types. Specifically, CFRs in the static swamp and lake wetlands were significantly higher than those in the lotic swamp and river wetlands, and CFRs in the swamp wetlands with emergent plants were significantly higher than those in the river and lake wetlands without emergent plant in summer. Stochastic processes dominated the assembly of bacterial communities associated with CO2-fixation, and the assembly processes also differed among wetland types. The distance-decay model revealed that geographical distance and environmental differences both caused variations in the bacterial communities associated with CO2-fixation among wetland types. Further analysis showed that the high levels of total organic carbon in the wetlands with relatively static water flow and abundant emergent plants are conducive to the growth of facultative autotrophic CO2-fixation bacteria, resulting in the variations in CFRs and the associated microbial communities among wetland types. This study expands the understanding of spatial distribution of carbon sequestration driven by microbes in wetlands.