Spatiotemporal Distribution Of Anaerobic Ammonia Oxi Dizing Bacteria And Microbial Communities In The Sediments Of Xiangxi River,Three Gorges Reservoir Region

The anaerobic ammonia oxidation reaction(Anammox)mediated by anaerobic ammonia oxidizing bacteria is an important part of the nitrogen biogeochemical cycle and has a significant impact on the global nitrogen cycle.The removal of anaerobic ammonium oxide is a process in which An AOB use nitrate and nitrite as electron acceptors and ammonia as an electron donor to be oxidized to N₂.The Three Gorges Reservoir area is located in the middle and upper reaches of the Yangtze River.Under the influence of human activities around the reservoir area,eutrophic bioremediation of water bodies in the reservoir area has become an important issue in the Yangtze River environment.An AOB could repair the excess N in water,but there were few related researches on the An AOB in the Three Gorges Reservoir area.In this paper,the sediments of the Xiangxi River,a typical tributary of the Three Gorges Reservoir area,were used as research objects to explore the spatial and temporal distribution of An AOB in the Three Gorges Reservoir area and its microbe community.In this study,a,b,c,d,and e were set up as sites from north to south along the Xiangxi River.All samples were taken along the Xiangxi River in different seasons(each 2cm was a sample).The physical and chemical indexes of samples were analyed by national standard method.Abundantce of An AOB was analyzed at the molecular level.Finally,the community of microbial flora(bacteria and archaea)in the sediment was studied.The main test results are as follows:1)TN and TOC content were from 0.66 g/Kg to 3.31g/Kg and 7.19 g/Kg to 30.03g/Kg.At the same time,the content of NO₃^--N was measured,the range was 0.10 mg/Kg?1.90 mg/Kg;the content of NO₂^--N was higher than NO₃^--N,the range was 2.14 mg/Kg?8.81 mg/Kg;NH₄⁺-N content range was 0.33 mg/Kg?2.56 mg/Kg;SO₄^2-varied from73.98 mg/Kg to 266.40 mg/Kg.2)The abundance of An AOB in the Xiangxi River sediments was discussed using q PCR technology.The results showed that An AOB was present in the Xiangxi River sediments,and the abundance was 1.45×10⁴?3.16×10⁹copies/g sediments,the abundance of An AOB changed greatly at different sites and different times.3)In time,the An AOB abundance in the 0?10cm sediments at the five sites in 2016was highest in autumn,and the a and e sites showed the same distribution,that is,autumn>winter>spring>summer.The An AOB abundance at a and e in 2017 showed the pattern of summer>winter>spring,and the b,c,and d showed Winter>Summer>Spring.4)The An AOB abundance in the sediments of the Xiangxi River in 2016 showed a spatially increasing trend with the vertical depth of the sediment,or a increasing trend first and then decreasing.In the horizontal space,the An AOB abundance of the sediments in the Xiangxi River showed a increasing trend from a site to e site.5)Spearman correlation analysis confirmed that An AOB abundance was significantly correlated with total nitrogen(TN)(P<0.01),NO₃^--N,and TOC(P<0.05)concentrations in sediments.Two-factor analysis of variance showed that there was no significant difference of An AOB abundance in different physical and chemical indicators(TN,TOC,NO₃^--N,NH₄⁺-N,NO₂^--N,SO₄^2-)and in different seasons.6)16S rRNA gene sequencing technology was used to identify the bacterial flora in the Xiangxi River sediments.The results showed that the bacterial groups were mainly Exiguobacterium,Citrobacter,Gp6 and Acinetobacter,the bacterial diversity of sediments in different seasons at the same site in the Xiangxi River was decreased with time(season),and the bacterial diversity at different sites in the spring gradually was increased from a to e,and diversity of bacteria in c site in the summer was the highest,and the lowest in summer in e site.7)Euryarchaeota,Crenarchaeoto and Thaumachaeoto are the main archaea.At the genera level,most of the methanogenic archaea were followed by Nitrososphaera and Nitrosopumilus,and the rest of the genera were relatively low.Methanoregula,Methanosalsum,Methanomassiliicoccus were the main methanogens in the sediment,and the community structure of each genus has changed due to seasonal(precipitation,temperature,etc.)environmental factors.The archaea diversity was also gradually decreased from south to north along the Xiangxi River.The diversity of archaea communities in the spring and winter at a site was higher than in summer,and the species diversity at c site was gradually decreased from spring to winter.The archaea diversity was no significant change in spring and summer of d site,and in spring and summer of e site.