The Structure Characteristics Of Planktonic Bacterial Community And Its Response To Physical And Chemical Factors In Danjiangkou Reservoir

The Danjiangkou Reservoir was an important water source for the middle route of the South-to-North Water Diversion Project.It was of great significance to study the composition of the ecological environment and the quality of the water body.Planktonic bacteria widely existed in various aquatic ecosystems,and were of great significance to the material circulation in the ecosystem.In order to comprehensively explore the composition and changes of bacterioplankton species in the Danjiangkou Reservoir area,as well as their interactions with physicochemical factors.Illumina Mi Seq high-throughput sequencing technology was used to investigate the composition,variation,distribution,community structure and functional metabolic composition of bacterial plankton in 132 samples collected from 11 sampling sites in the Danjiangkou Reservoir area and its tributaries in 2018and 2019.The relationship between phytoplankton community and physical and chemical factors in surface waters of Danjiangkou Reservoir area and its tributaries was discussed based on the detection results.The main findings are as follows:1.Monitoring analysis showed that,except for total nitrogen,all indicators in the Danjiangkou Reservoir area meet the surface water standard of Class II and above.The water quality of the reservoir area was better than that of tributaries,and the overall water quality was better.The Planktonic bacteria in Danjiangkou reservoir were composed of 13 phyla,21 classes,48 orders and 68 families.Ilumatobacteraceae of actinomycetes was the dominant taxa of Planktonic bacteria in Danjiangkou Reservoir.Spearman correlation analysis showed that DO and SD were significantly positive correlated with them,while Cond,COD_Mn and TP were significantly negative correlated with them.Random forest analysis showed that Holophagaceae of Acidobacteria and Aeromonadaceae of Proteobacteria were important landmark groups of plankton community in Danjiangkou Reservoir.2.The?diversity index of planktonic bacteria showed that the community richness and diversity in tributaries were greater than those in the Danjiangkou Reservoir area.Except for the Dashiqiao sampling site,the community diversity in spring was higher than that in autumn.The difference of bacterial community showed a downward trend,and the composition of community structure tended to be stable.The community composition of the four sampling samples was significantly affected by different physical and chemical factors,WT and SD were negatively correlated with the community richness index,while COD,COD_Mn,Cond,NH₄⁺-N,NO₃^--N,TN and TP were positively correlated with the community richness index.WT and p H were negatively correlated with the community diversity index,while COD_Mn,NH₄⁺-N,Cond,COD,NO₃^--N and TP were positively correlated with the community diversity index.The results of variance decomposition showed that nitrogen and phosphorus had the lowest explanation for the composition of plankton in the Danjiangkou reservoir area.3.Molecular network analysis showed that the number of molecular network nodes in Danjiangkou reservoir increased gradually,indicating that the community structure was more stable.The importance network nodes of samples in each sampling period were different.TN and TP were the common important nodes of molecular network analysis of two samples collected in 2018,and WT was the common important nodes of molecular network analysis of two samples collected in 2019.The connectivity of physical and chemical factors and species groups in the composition of Planktonic bacteria community in specific habitats was revealed.4.Functional prediction showed that amino acid transport and metabolism,translation,ribosomal structure and biogenesis,energy production and conversion were the three most abundant functional genes in the 25 functional gene families.Metabolic pathway study found that there were 6 primary metabolic pathways,46 secondary metabolic pathways and 405tertiary metabolic pathways.Metabolism was the most abundant in the primary metabolic pathway,and global and overview maps were the most abundant in the secondary metabolic pathway.The five metabolic pathways with the highest abundance in tertiary metabolic pathways were all classified as Global and overview maps secondary metabolic pathways and metabolic primary metabolic pathways.It showed the diversity of Planktonic bacteria community in function and metabolic pathway in Danjiangkou reservoir.In this study,the phytoplankton community composition and its relationship with physical and chemical factors in Danjiangkou Reservoir were investigated by high-throughput sequencing technology,in order to provide reference for the aquatic ecosystem security of Danjiangkou reservoir.