Abundance and diversity of carbon-fixing bacterial communities in karst wetland soil ecosystems

• Soil carbon-fixing bacterial communities in a karst wetland were characterized. • Abundance of cbbL gene was higher than that of cbbM gene in karst wetland soils. • Dominant bacterial genera were significantly different among karst wetland soils. • SOC and its fractions affected soil carbon-fixing microbail community structure. • Wetland reclamation changed soil carbon-fixing microbial community structure. Autotrophic carbon-fixing bacteria are the main drivers of carbon sequestration and elemental cycle in wetland ecosystems. Their relationship with environmental factors in karst soils such as soil organic carbon (SOC) fractions, which are affected by natural degradation and human disturbance, is key to understanding the biological mechanisms of karst wetland ecosystem deterioration and restoration. In this study, the abundances of the Calvin cycle functional genes cbbL and cbbM as well as the characteristics of carbon-fixing bacterial communities were compared in soil samples from a native wetland, naturally degraded wetland, and reclaimed farmland wetland in the Huixian karst wetland, Guilin, China. The abundances of the cbbL gene in the degraded wetland and reclaimed wetland soils varied significantly among the seasons ( P < 0.05, summer > winter). The influence of the season on the abundances of the cbbL and cbbM genes was more significant than that of the wetland state. The structures of carbon-fixing bacterial communities were similar in the three states of karst wetland soils, mainly consisting of Alphaproteobacteria , Betaproteobacteria and Gammaproteobacteria in the phylum Proteobacteria . However, the relative abundances of some dominant bacterial genera were significantly different. Thiomonas and Bradyrhizobium had a relatively high abundance in the native wetland soil and the degraded wetland soil, respectively, while Ferriphaselus and Sulfuricaulis were more abundant in the reclaimed farmland wetland soil. The main soil factors affecting the structure of the carbon-fixing bacterial communities were the SOC and its fractions dissolved organic carbon (DOC), microbial biomass carbon (MBC) and readily oxidizable organic carbon (ROC), as well as the soil temperature. Anthropogenic activities such as wetland transition to farmland have caused significant changes in karst soils and the characteristics of carbon-fixing bacterial community in this karst wetland soil ecosystem.