Spatial And Temporal Differences Of The Ammonina-Oxidizing Archaea Community Structure In The Sediments Of Two Estuaries In Chaohu Lake

In recent years, more and more evidences suggest that ammonia-oxidizing archaea（AOA） exert potentially important roles in ammonia oxidation process which is the keypart in the nitrification, and have some impact on maintaining the balance of the globalnitrogen cycling and adjusting global climate. AOA communities also make a certaineffect in biological repair to eutropication caused by anthropogenic nitrogen emissions inestuary, lake and coastal marine ecosystems. However, recent studies for AOA communitymainly focus on the soil and marine water and sediment ecosystems, only few involved infreshwater lake ecosystems, especially estuarine sediment ecosystems. In this study,sediment samples were collected in Nanfei River and Xinhe River estuaries from March,June, September and December in2010. Using molecular ecology techniques and analysismethods, spatial and temporal differences of AOA community structure, diversity andabundance were investigated, and relationship between AOA community distribution andenvironmental parameters of sediments was analyzed. The main results are as follows:There were significant differences in environmental parameters in the sediments ofNanfei River （NF） and Xinhe River （XH） estuaries. In each sampling site, the seasonaltemperature variation was great, and the pH values were lowest in December, which weredistinct from the pH values in other three months. TN, NH₄+^-N, NO₂--N, NO₃--N and OrgNconcentration were higher in March and June, but were lower in September and Decemberin both two estuaries. In each month, the little differences of sedimental temperature andpH values occurred between the two estuaries. The annual average concentrations of TP,IP, TN, NH₄⁺-N, NO₃^--N and OrgN in the sediment of NF were higher than those of XH.The eight amoA gene cloning libraries obtained from four months in two estuarieswere analyzed by using the PCR-RFLP method and mothur v1.3software, and obtained24OTUs, of which14occurred in NF and21occurred in XH.The results of diversity indices （H and S） and richness index （Schao1） of AOAcommunity indicated that the diversity and richness of AOA community in the twoestuaries showed the same trend of spatio-temporal difference. In each estuary, the H and S indices were highest in the sediment in June, but diversity and richness indices were lowestin December. In each month, H, S and Schao1indices in March and December in NF werehigher than those in XH, and those in June and September were lower than those in XH. Ingeneral, H, S and Schao1indices in NF were lower than those in XH.The PCoA results showed that eight AOA communities divided into four groups. TheAOA communities in March, June and September in NF were grouped together; those inJune and September in XH and those in December in NF were grouped together; those inMarch and December were independent as one group respectively. Compared thesimilarities of AOA community in each samples, the same result were obtained. About43%AOA genotypes were shared by four sediment samples in NF, and Jabundand θ valuesof AOA communities in XH were low, with Jabundvalues ranged from0.17to0.58and θvalues ranged from0.14to0.30.The phylogenetic analysis of AOA indicated that AOA populations in the sedimentsin Chaohu Lake were mainly related with those in agricultural soils and freshwater riverand lake sediments. Some unique AOA ecotypes were existed in NF and XH sediments.The AOA community distribution was influenced with the changes of environmentalfactors, and presence a certain spatial and temporal differences.Quantitative analysis of AOA amoA gene suggested that the copy number of amoAgene in June in NF was lowest （4.29×10⁶copies/g）, and that in December was highest（7.6×10⁷copies/g）; the copy number in XH was from the lowest （9.53×10⁵copies/g） inMarch to the highest （2.24×10⁷copies/g） in December. The ratios of copy number ofNF/XH were from3.2to10.9in March, September and December, that in June was3.3.Canonical correspondence analysis （CCA） showed that NH4+-N, NO2--N concentrationsand temperature had more influence on the spatio-temporal distributions of AOAcommunities in the sediments of freshwater estuaries. The results of the Spearman rankcorrelation coefficient, the AOA abundance were significantly correlated with TN andOrgN content in the sediment of the two estuaries in Chaohu Lake.