| Three Gorges Reservoir(TGR)is a developing ecosystem duo to anti-seasonal hydrology character.The input and output materials is changing the sediments environment of TGR.Microbial community plays an important role in the elements cycle in sediment-water ecosystem.Nitrogen is basic nutrition for microorganism and also can deteriorate water quality(eg.eutrophication).Microbial nitrogen cycle is important in nitrogen cycle.However,the dynamics of elements,microbial community structure,and nitrification and denitrification in TGR sediments remains unknown.Study on these processes will help us to better understand the microbial system stability and nitrogen cycle of TGR and also provide the theoretical basis for utilization of microbial community resource and assessment the ecosystem stability.In this study,we sampled sediments and overlying water samples from South River,Hanfeng Lake,and Pengxi River along Xiaojiang River in TGR during 2014-2015 water impounding and dischargingperiod.We analyzed the physiochemical property of sediments and water,determined the nitrification and denitrification rates of sediments using acetylene inhabitation method,assessed denitrification functional genes(nirK,nirS,nosZ)and the total bacterial 16 S rRNA gene by qPCR,and obtained bacteria community structure by high throughput MiSeq sequencing.We then used one-way-ANOVA and person correlation to test the variation and the relationship of data,respectively.Finnaly,we used multivariate analysis to assess how environment factors impact the microbial community.The main results are as follows:1.There were significant differences in the water level between the overlying water and sedimentary physiochemical parameters in the Xiaojiang watershed(p<0.01~ 0.05).The concentrations of physiochemical parameters(sediment: total nitrogen,ammonia nitrogen,nitrate nitrogen,total phosphorus,total organic carbon;overlying water: total nitrogen,ammonia nitrogen,total organic carbon)at impounding period were significant higher than that atdischarging period.The physiochemical parameters of sediments and overlying water in Xiaojiang watershed are significantly affected by the surrounding environmental factors such as the area of land,the area of water and drop.While the overlying water and sedimentation physiochemical factors have a strong correlation.2.At 2015 year,nitrification rates in sediments at South River,Hanfeng Lake and Pengxi River were [16.52 ± 20.09~194.06±151.90 ?mol·(m2·h)-1],[39.69±41.19 ~ 229.56±144.08 ?mol·(m2·h)-1],[31.27±42.21~72.54±64.07 ?mol·(m2·h)-1],respectively.Denitrification rate were [24.04±364.12~647.20±127.32 ?mol·(m2·h)-1],[95.24±79.82~219.21±150.55?mol·(m2·h)-1],[73.38±6.10~425.61±330.71 ?mol·(m2·h)-1],respectively.In South river,nitrification rate in sediments during water impounding period was significant higher than that in discharging period.The rate was also positively correlated to the physiochemical parameters(total nitrogen,nitrate,ammonia,and total organic carbon).In contract,nitrification rate in sediments of Hanfeng Lake and Pengxi River was higher in water discharging period.There was no significant correlation with the physiochemical parameters of sediments and the rates.Denitrification rate in all sediments at discharging period were generally significantly higher than that in sediments at impounding period.Denitrification rate in sediments from South River was negatively correlated to the physiochemical parameters(total nitrogen,nitrate,ammonia).Still,there was no correlation between the rate and physiochemical parameters in Hanfeng Lake and Pengxi River.The number of nitrifying and denitrifying bacteria in the sediments of the third basin is the main factor affecting the rate of nitrification and denitrification(p <0.05).3.During 14-15 years,the range of nirK gene abundance in sediment at South River,Hanfeng Lake and Pengxi River were 9.49×10-9~5.71×10-5,1.08×10-7~1.59×10-6,1.22×10-8~1.19×10-5,respectively.The range of nosZ gene abundance were 1.84×10-6~1.10×10-2,2.86×10-6~1.44×10-2,5.89×10-7~7.69×10-3,respectively.The range of nirS gene abundance were2.79×10-5~4.09×10-1,2.73×10-5~1.07×10-1,3.82×10-5~4.81×10-2,respectively.Gene nirS is the highest gene,followed by nosZand nirK(p < 0.05).Total nitrogen,pH,and ammonia are the main physiochemical parameters affecting the denitrification genes in sediments(p<0.05).Denitrification funcation genes(nirS)was positively correlated to the nitrification rate.However,there was no significant correlation with the denitrification funcation genes and denitrification rates of sediments.4.There are 53 phylum,144 classes,332 orders,676 families,and 1035 genus of bacteria detected in sediment samples.Microbial composition and diversity showed seasonal variation.For all samples,the most commonly detected phyla were Proteobacteria,Bacteroidetes,Acidobacteria,Chloroflexi,Nitrospirae,Actinobacteria,Verrucomicrobia,Firmicutes,Gemmatimonadetes,Planctomycetes,Chlorobi,Latescibacteria et al.Among then,Proteobacteria,Bacteroidetes,Acidobacteria and Chloroflexi were the dominant of bacterial groups,accounting for > 70% of total abundance.Proteobacteria predominated in all samples.RDA analysis showed that nitrogen was the main environmental factors affected the composition of bacterial communities in sediments.5.Sediment nitrification bacteria in the Xiaojiang watershed were mainly included: Nitrospina,Nitrospira,Nitrosomonas,Nitrosospira,Nitrosococcus et al.Among then,Nitrospira was the dominant of bacterial groups,abundance of 0.08%~9.16%.Denitrification bacteria mainly included: Pseudomonas,Bacillus,Achromobacter,Alcaligenes et al.Among then,Pseudomonas was the dominant of bacterial groups,abundance of 0.04%~9.24%.RDA analysis showed that pH of sediment was the main environmental factors affected the main nitrification and denitrification bacteria in South river.There was no significant effected with the physiochemical parameters of sediments and the main nitrification and denitrification bacteriain other watersheds. |
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