Abstract:The aim of the study was to investigate the diversity and community structure of autotrophic carbon dioxide-fixing bacteria by DNA-based stable isotope probing (DNA-SIP) technology and microcosm model method in no-till paddy soil in South China. The total DNAs by CsCl density-gradient centrifugation were separated on the basis of the buoyant density distinguishing after an 80-day incubation as templates, it showed that the carbon dioxide-fixing autotrophic microbes can assimilate and utilize carbon dioxide in soil. The RFLP-PCR showed that the highest copies of the cbbLR gene from two kinds of soil samples were 1.36×105 copies/g dry soil and 2.21×105 copies/g dry soil, respectively. The structure of carbon dioxide-fixing autotrophic microbial communities were significantly different from each other by clone library and phylogenesis analysis. Bradyrhizobium and Rubrivivax were the main microorganisms in soil FG and accounted for 60.40% and 13.86% of all clones, respectively. The community composition of carbon dioxide-fixing bacteria in soil TF was relatively uniform, and Rhodopseudomonas, Bradyrhizobium, Methylibium and Variovorax accounted for 20.92%, 11.94%, 16.42% and 10.45% of the total clones, respectively. The number of OTUs and diversity index of 13C-carbon dioxide stable isotope labeled cbbLR library were higher than these of the 12C-carbon dioxide labelled control library, and the community structure also showed significant differences. Together, we conclude that there are diverse autotrophic bacteria capable of fixing carbon dioxide in the no-tillage paddy soil, and they have an important role in the carbon cycling for farmland soils.