Study On The Characteristics Of Ammonia-Oxidizing Microbial Community And Ammonia-Oxidizing Action In The Sediments Of Lantsang River Cascade Reservoirs

The cascade development of Lantsang River basin not only promotes the regional economic and social development,but also receives extensive social attention for its impact on the environment and ecology.Nitrogen is the main element that constitutes the important living matter,and it is also the basis for maintaining the composition of various biological structures and carrying out various biochemical activities.With the construction of cascade reservoirs of Lantsang River,the characteristics of river sediments have changed obviously under the condition of dam interception.As an important source and sink of nitrogen circulation in reservoirs,sediments are also important substrates for the survival and development of microorganisms,which have an important influence on the changes of nitrogen circulation in cascade reservoirs.In this study,Xiaowan,Manwan,Dachaoshan,Nuozhadu and Jinghong reservoirs of the Lantsang River which were built earlier.These reservoirs were selected as the research objects to systematically study the abundance,diversity and community characteristics of ammonia-oxidized microorganisms in the sediments of the cascade reservoirs.The main research conclusions were as follows:（1）Spatial heterogeneity of physical and chemical factors of sediment and overlying water was analyzed.The research results showed that the sediment pollution degree was different in different areas of cascade reservoirs of Lantsang River,and the content of NO₃^--N and NO₂^--N was significantly lower than that of NH₄⁺-N.TN showed a gradually increasing trend in spatial variation,and the content of NO₂^--N,NO₃^--N,SOM and TN at the sample sites of NZD was the highest compared with the other five sample sites.The pH showed a gradually decreasing trend in spatial variation.SOM had extremely significant difference in content at six sample sites（p<0.01）,while NO₃^--N,NO₂^--N at the sample site of NZD and JH had extremely significant difference（p<0.01）.In the overlying water,TN first decreases and then increases in spatial variation,and NO₃^--N fluctuates between 0.32mg/L and 2.14mg/L.In the six sample sites,COD content was significantly higher than other physical and chemical indicators.（2）The abundance,diversity and community structure characteristics of AOA and AOB were investigated,and the key environmental factors affecting community distribution were identified.The results showed that the rules of succession of the dominant taxa of bacteria in different sediment sites were different in the process of spatial succession.The results of TRFLP experiment showed that OTUs,Simpson index,Shannon-Weiner diversity index and Evenness index of AOA community were all higher than those of AOB community.The T-RFs of AOA and AOB were concentrated in 58～270bp and 90～180bp respectively.Compared with the TRFLP atlas of AOA and AOB,the structure of AOA was simpler,and the enzyme fragment of each site was obviously different.Through CCA analysis and Pearson analysis of the key environmental factors affecting the T-RFs distribution of AOA and AOB advantages,the results showed that pH and NO₃^--N were the most significant factors affecting AOA advantages T-RFs,and NH₄⁺-N,NO₃^--N and SOM were the significant factors affecting AOB advantages T-RFs.Through QPCR experiment,the quantity of AOA was one order of magnitude higher than that of AOB in six points.The experiment of 16S rDNA sequencing showed that the dominant taxon of bacteria at each sediment point had the phenomenon of succession in spatial variation,but different taxon had different rules in the process of spatial succession.（3）The activity of AOA and AOB and their relative contribution to ammonia oxidation were investigated under different conditions by single factor culture experiment.The results showed that the ammonia oxidation rates of AOA and AOB were inhibited under the conditions of pH=4.5 and pH=10.5.Under four different pH conditions,AOA’s ammonia oxidation rate varied from（0.305±0.007）μg N/g·soil·d～（0.893±0.005）μg N/g·soil·d,and AOB’s ammonia oxidation rate varied from（0.117±0.001）μg N/g·soil·d～（0.608±0.017）μg N/g·soil·d.Through indoor ammonia nitrogen single factor culture experiment,it was found that increasing ammonia nitrogen of a certain concentration will increase the relative contribution rate of AOA and AOB to ammonia oxidation.When it was added the concentration of ammonia nitrogen A3=150 mol/L,the ammonia oxidation rate of AOA is inhibited at the sample sites of MWN04,DCS and JH.