Characteristic Of CO₂-Fixation Bacteria's Community Structure In Paddy Soils Under Elevated CO₂ Concentration

As the atmospheric carbon dioxide concentration continues to rise,the Earth's climate is undergoing global warming as the main characteristics of the ecological environment changes since the mid-19th century.The first important measure for mitigation and adaptation on climate change is controlling CO2 emissions.Autotrophic microbes can fix C02 through several paths,it is an important CO2 fixation power.Therefore,research on this process is of great significance for mitigating global warming.The aim of this study was to investigate the diversity or community structure of autotrophic CO2-fixing bacteria and responses of soil autotrophic bacteria to elevated CO2 in different layer depths of no-till paddy soil in South China,by using fluorescence real-time quantification PCR echnology and DNA-based stable isotope probing technology and combining with Illumina Miseq high-throughput sequencing technology.Main results for this study are as follows:The soil of different layer depths were cultured for 70 days under elevated CO2(40 000 ppm).The results of real-time PCR show that 16S rRNA gene copy number between 1010?1012 copies/gram of dry soil and the CO2 fixation related marker gene copy number range is 105?109 copies/gram of dry soil,copy number's laws is cbbLR>coxL>cbbM>cbbLG and the copy number of each gene was gradually decreased with the increase of soil depth.Moreover,the coefficient of variation of the copy number of functional gene during the whole culture period showed moderate variability,which showed the law of the plough layer or plow pan>percogenic horizon.The cbbM functional gene was sequenced by Illumina Miseq platform.Results showed that the diversity indices as well as variation coefficient calculated based on diversity indices follow the same trend in different incubation time that plough layer>plow pan or percogenic horizon.VENN diagram showed that the surface layer soil possess more unique OTUs than that of the deeper soil.The principal co-ordinate analysis,the weighted UniFrac principal co-ordinate analysis(based on OTU),and the principal component analysis(based on genera)all showed huge differences among different soil layers.The community similarity analysis showed that plough layer was less affected by high concentration of CO2,but with the increase of soil depth,communities were more affected by evaluated CO2 concentration.The type RubisCO form ? autotrophic bacteria group including alpha-/beta-and gamma-proteobacteria in different layer depths of FG and TF soil.In the FG soil,phylogenetic analysis showed that Thiobacillus,Sulfuritalea,Acidihalobacter and Magnetospirillum(relative abundance>5%)were the dominant autotrophic bacteria in plough layer soil;Sulfuricella,Thiocystis,Halothiobacillus and Thiobacillus were the dominant autotrophic bacteria in plow pan or percogenic horizon soil.In the TF soil,sequence-based analyses of the sequence data indicated that Thiobacillus,Thiocystis,Acidihalobacter,Sulfuritalea,Halothiobacillus and Rhodopseudomonas were the dominant taxa at the plough layer soil;Halothiobacillus,Thiocystis,Sulfuricella and Thiobacillus were the dominant taxa at the plow pan soil;The dominant autotrophic bacterias of the percogenic horizon soil are Magnetospirillum,Halothiobacillus and Thiocystis.The advantages of carbon fixing bacteria in different layers of soils are mostly autotrophic bacteria,and most of these are also associated with sulfur oxidation.In order to investigate the diversity of cbbM gene in paddy soil,by combining DNA-based stable isotope probing(SIP)and high-throughput pyrosequencing,our results show that Thiobacillus(26.92%),Sulfuritalea(22.13%),Acidihalobacter(12.59%),Thiohalospira(10.08%),Halothiobacillus(2.08%)and Acidithiobacillus(1.86%)dominated active RubisCO ? autotrophic microorganisms in FG no-till paddy soil in South China.and Sulfuritalea(15.92%),Thiohalospira(6.30%),Acidihalobacter(3.41%),Thiobacillus(1.21%),Rhodovulum(1.06%)and Acidithiobacillus(1.01%)dominated active RubisCO ?autotrophic microorganisms in TF soil.There were significant differences between the dominant autotrophic microorganisms in FG and TF soil,but all with obligative and facultative sulfur-based bacteria.