Community Composition Of Dissimilatory Nitrate Reduction To Ammonium(DNRA) Bacteria In Systems Of Paddy Field And The Riparian Zone Of Wetland

At present,the amount of man-made nitrogen fixation is far more than the sum of natural nitrogen fixation,the balance of nitrogen cycle has been seriously damaged,and the problem of nitrogen pollution is serious.Nitrate dissimilatory nitrate reduction to ammonium?DNRA?is one of the key processes of microbial nitrogen cycle,in which NO₃^-/NO2-is the electron acceptor and NADH is oxidized to produce NH₄⁺,without greenhouse effect.At present,the research on DNRA process and its related microbial community structure is insufficient at home and abroad.DNRA process in farmland is helpful to the preservation of nitrogen in soil.Wetland riparian zone is a transitional zone from terrestrial ecosystem to aquatic ecosystem.DNRA process plays a key role in the removal of groundwater pollutant NO₃^-in the process.DNRA process in vertical ecosystem of paddy field and wetland riparian system is studied,and key bacteria and their environmental impact factors are explored.Retention and purification of wetland wastewater are of great significance.In this paper,molecular biology,high-throughput sequencing of DNRA bacterial functional gene nrfA and 15 N stable isotope tracing techniques were used to study the vertical soil and constructed wetland ecosystems in paddy fields.In the study of vertical soil ecosystem in paddy field,Shaoguan summer paddy field,Shaoguan winter paddy field and Antu summer paddy field were selected as the research objects.The vertical distribution characteristics of DNRA bacterial abundance and community structure and the activity of DNRA bacteria in paddy field soil?0-1 m?were studied.The results showed that the abundance of DNRA bacteria in paddy soil samples ranged from?9.99±0.04?103 to?3.60±0.05?108 copies g-1,and the proportion of DNRA bacteria in total bacteria ranged from 0.07% to 18.32%.In the vertical soil of paddy field,DNRA bacteria were more found in the surface soil?0 cm-20 cm?,and the lowest abundances were found in the deep soil?90 cm-100 cm?.On the whole,the abundance of DNRA bacteria in Antu paddy soil samples was higher than that in Shaoguan paddy soil samples;on the surface of soil,the abundance of DNRA bacteria in Shaoguan paddy soil samples in summer was higher than that in Shaoguan winter samples,while there was no specific law in other soil layers.Diversity analysis?OTUs level?showed that the diversity of community structure in surface layer of paddy field was greater than that in deep layer of paddy field,and the diversity of bacterial community structure in subsurface layer of soil?10 cm-20 cm?was the highest.The community structure of two paddy field samples showed obvious spatial heterogeneity.The diversity of DNRA bacteria community structure in Antu paddy field was higher than that in Shaoguan paddy field.The diversity of soil samples in Shaoguan in summer was higher than that in winter between 0 cm and 30 cm.PCo A analysis?OTUs level?and cluster analysis showed that soil samples belonging to the same paddy field were clustered together preferentially.Soil samples of the same soil depth were clustered together.At last,soil samples of the same season were clustered together.Geographical environmental factors of different sampling sites were the biggest factors affecting the bacterial community structure of DNRA,followed by soil depth,and season had little effect on the bacterial community structure of DNRA.DNRA bacteria in paddy soil samples were annotated to 13 phyla and 35 genera.Proteus,Proteobacteria,Thermodesulfobacteria and Nitrospirae were the main bacterial types.Anaeromyxobacter,Caldimicrobium and Nitrospira are the key bacterial species in DNRA bacterial community of paddy soil samples,while relatively low abundance species such as Haliangium?2.9%?and Candidate Promineofilum?1.9%?also play an important role in DNRA bacterial community.The correlation analysis of vertical soil physical and chemical factors in paddy field showed that NH₄⁺,p H,TS,TOM,moisture content?MC?,TN,TC and C/N were significantly positively correlated with bacterial abundance of DNRA,while NO₃^-was negatively correlated with bacterial abundance of DNRA.The activity of DNRA bacteria could only be detected in 0-30 cm soil layer,but not in other soil layers.In the study of Shijiuyang constructed wetland in Jiaxing,the distribution characteristics of DNRA bacterial abundance and community structure in wetland sediments were studied at four research sites: the center of Large ditch,the fringe of Large ditch,the center of Small ditch and the margin of Small ditch.The results showed that the abundance of DNRA bacteria ranged from?1.70±2.79?107 to?2.55±0.15?108 copies g-1,and the proportion of DNRA bacteria in total bacteria was 0.73% to 2.54%.DNRA bacteria mostly exist in the center of ditches,and the abundance of DNRA bacteria in the center of ditches is greater than that in the edge of ditches.PCo A analysis?OTUs level?and cluster analysis showed that the composition of DNRA community was mainly affected by different sampling sites.The bacterial community structure of DNRA in the same sampling sites was similar,and the influence of the center and edge of ditches on the community structure was small.The diversity of community structure in the center of small gully is the largest,while that in the edge of big gully is the smallest.DNRA bacteria in constructed wetland sediment samples have high diversity and many species of bacteria.DNRA bacteria in the samples have been annotated to 14 phyla and 55 genera.Proteus,Proteobacteria,Thermodesulfobacteria and Chloroflexi are the main bacterial types.Network analysis shows that the key bacteria in DNRA bacterial community of wetland sediment are Anaeromyxobacter,Caldimicrobium,Haliangium,Caldiline,Hodiline.Lower abundance species,such as Sorangium and Bdellovibrio,also play an important role in DNRA communities.The correlation analysis showed that the abundance of DNRA bacteria was positively correlated with TOM,MC,TN,TC,TS,C/N,and negatively correlated with NO₃^-significantly.According to the above research on DNRA process in vertical soil and constructed wetland ecosystems of paddy field,it is found that DNRA bacteria are abundant in paddy field and wetland systems,with alkaline,rich organic matter,lack of nitrogen sources,rich carbon sources and high C/N ratio,as well as suitable water content,which is the suitable living environment for DNRA bacteria in paddy field and wetland systems.Regulation of water resources and soil conditions in paddy fields and wetlands,optimization of community structure of DNRA bacteria in paddy fields and coastal zones of wetlands,and enhancement of dominant microorganisms of DNRA bacteria are of great significance for improving nitrogen utilization efficiency,sewage purification and reducing nitrogen pollution in farmlands.