Study On Microbial Community Diversity And Its Response To Environmental Factors In Li River

Li River belongs to Huaihe River Basin and Yinghe River System.It originated in Fangcheng County,Nanyang City,flows through Ye County and Wuyang County,and flows into Shahe River in Yuanhui District,Luohe City.In this paper,Li River was taken as the research object,16S rRNA V3-V4 region was taken as the target gene,and high-throughput sequencing was carried out based on Illumina platform.By using bioinformatics analysis technology,the spatio-temporal variation of microbial diversity in water body of Li River,sediments along the riverbank,rhizosphere and non-rhizosphere sediments of Miscanthus sacchariflorus and its response to environmental factors were systematically studied.The results are as follows:(1)From October 2020 to August 2021,18 sampling points were set up along the Li River,and 72 water samples were collected for four consecutive quarters.The measurement results of water environmental factors show that the water quality of Li River is generally good,and the water quality indexes TP,COD,NH3-N and DO can reach Class Ⅲ of surface water environmental quality standard in autumn and ClassⅣ of surface water environmental quality standard in winter,spring and summer.In this study,5,079,452 valid sequences were obtained from 72 water samples,which can be divided into 8,941 OTUs based on 97%similarity.The a diversity analysis shows that the a diversity of microorganisms is the highest in summer,which is due to the heavy rainfall in summer,and the surface runoff carries a large number of terrestrial microorganisms into the water body.Based on the correlation analysis between environmental factors and microbial community,the results show that the key environmental factors affecting microbial community structure in water are DO,T and TP.The microbial population structure of Li River showed great differences in four quarters,among which Proteobacteria and Actinobacteria were the dominant flora in four quarters,but their proportions fluctuated greatly with the change of seasons.In addition,Firmicutes appeared in the dominant flora in autumn and spring,while Bacteroidetes and Cyanobacteria appeared in the dominant flora in winter and summer respectively.(2)In this study,16 sediment sampling points were set up along the river bank,and 64 sediment samples were collected for four consecutive quarters.The analysis of environmental factors of sediment samples showed that NH3-N,NO2-N and pH of autumn samples were significantly higher than those of other seasons(p≤0.05),and NO2-N had no significant difference with summer samples.The contents of TKN,TP and NO3-N in winter samples are significantly higher than those in other seasons(p≤0.05),among which TKN and TP are not significantly different from summer samples,and NO3-N is not significantly different from spring samples.The NO3-N level in spring samples was significantly higher than that in autumn and summer(p≤0.05).There is no significant difference in TOC among samples in different seasons.In this study,4,826,771 valid sequences were obtained from 64 sediment samples along the river bank,which can be divided into 12,211 OTUs based on 97%similarity.The a diversity analysis showed that the microbial richness of samples in autumn and summer was significantly higher than that in winter and spring.The diversity of samples is the highest in summer and the lowest in autumn.Based on the correlation analysis between environmental factors and microbial community,the results show that the key environmental factors that affect the microbial community structure in sediments along the river bank are NH3-N,NO3-N and pH.Compared with water samples,the microbial community structure of sediments along the banks of the Li River changed little in four quarters,but the proportion of dominant flora still changed with time and space.On the whole,the dominant flora in the four seasons are Proteobacteria,Bacteroidetes and Acidobacteria.Especially,in summer,the relative abundance of Acidobacteria exceeds that of Bacteroidetes.(3)In this study,the sediment/soil columnar samples from four different habitats(river bottom sediment,wetland sediment,dam soil and farmland soil)along the Li River were collected at sampling point No.4 to study the diversity of microbial community structure and its response to environmental factors in different depths of sediment/soil(surface layer 0-10 cm,middle layer 11-20 cm and bottom layer 21-30 cm).The results of environmental factors measurement showed that TKN,TOC,NH3-N and pH of CS1 group were significantly higher than those of other groups(p<0.05),among which TOC and pH had no significant difference compared with CS2 group.The TOC and pH of CS2 group were significantly higher than those of CS3 and CS4 group(p<0.05).TP of CS3 group was significantly higher than that of other groups(p<0.05).The NO3-N content of CS4 group was significantly higher than that of other groups(p<0.05).In this study,1,527,644 valid sequences were obtained from 12 environmental samples,which can be divided into 3,530 OTUs based on 97%similarity.α diversity analysis showed that the microbial richness and diversity in CS3 group was significantly the lowest(p<0.05),while the microbial diversity and richness in CS2 and CS4 groups were significantly the highest(p<0.05),and a diversity also fluctuated greatly at different depths.Based on the correlation analysis between environmental factors and microbial communities,the results show that TP and NO3-N are the key factors affecting microbial community structure in sediment/soil columnar samples.Microbial communities show great differences in different spaces,among which Proteobacteria is the dominant flora in the four groups and accounts for the highest proportion.Bacteroidetes is the dominant flora in CS1-CS3 groups,besides,Firmicutes appeared in CS1 and CS3 groups,Acidobacteria appeared in CS2 group;In CS4 group,Proteobacteria kept the dominant proportion,while Acidobacteria and Actinobacteria became the dominant flora.Influenced by the change of environmental factors and the limitation of microbial diffusion,the difference of microbes in different sampling areas is greater than that in different depths of the same sampling site.(4)In this study,five sampling points were selected along the Li River,and rhizosphere/non-rhizosphere sediment samples of Miscanthus sacchariflorus were collected respectively.Physicochemical parameters of rhizosphere sediments of Miscanthus sacchariflorus showed some differences in different areas.TKN,TP,TOC,NH3-N and NO3-N in S1 group were significantly higher than those in other groups(p<0.05),but TP and NH3-N had no significant difference compared with S2 group.The NO3-N of S2 group was significantly higher than that of other groups(p<0.05).Compared with S4 group,the pH of S3 group was not significantly different,but significantly higher than that of other groups(p<0.05).The NO2-N of S4 group is significantly higher than that of other groups(p<0.05).In this study,790,155 valid sequences were obtained from 5 rhizosphere samples and 5 non-rhizosphere samples,which can be divided into 3,299 OTUs based on 97%similarity.The a diversity analysis showed that the a diversity of rhizosphere sediments was slightly higher than that of non-rhizosphere sediments,but there was no significant difference.Based on the correlation analysis between environmental factors and microbial communities,the results show that TKN,NH3-N and pH are the key environmental factors that affect the microbial community structure in rhizosphere/non-rhizosphere sediments.Microbial communities show great differences in different spaces,and the proportion of Proteobacteria,Bacteroidetes and Acidobacteria as dominant flora in different sites fluctuates greatly,but there is no significant difference between rhizosphere and non-rhizosphere sediment samples of Miscanthus sacchariflorus.Plants can produce rhizosphere effect and enrich a large number of microorganisms in rhizosphere.However,the results show that Miscanthus sacchariflorus didn’t produce significant rhizosphere effect,which may be caused by the neutral pH range reducing the availability of nutrients.Comparative analysis of microorganisms in rhizosphere sediments and non-rhizosphere sediments shows that there are a large number of Dokdonella in rhizosphere sediments,which belongs to the biological indicator of phthalate esters.It is speculated that Miscanthus sacchariflorus can secrete phthalate esters and promote the enrichment of Dokdonella in rhizosphere sediments of Miscanthus sacchariflorus.In this paper,the diversity of microbial community structure in the Li River Basin was systematically studied for the first time,and the environmental factors affecting the change of microbial community structure were analyzed,which laid a solid foundation for understanding the distribution of microbial community in the freshwater ecological environment and provided reliable data for the protection of water ecological environment in the Li River Basin.