The Structure Characteristics And Driving Factors Of Plankton Eukaryotic Community And Evaluation Of Water Quality Driving Factors In Danjiangkou Reservoir

Plankton existed widely in aquatic ecosystems and played a key role in nutrient flow and energy cycle.In order to fully understanded the composition and evolution of planktonic eukaryotes in Danjiangkou Reservoir and maintained the water ecological balance in the water source area of the Middle Route of South-to-North Water Diversion Project.A total of132 samples were collected from 11 sites in Danjiangkou Reservoir in 2018 and 2019,and the abundance and diversity of planktonic eukaryotes in the surface water of Danjiangkou Reservoir were analyzed by using 18S r DNA high-throughput sequencing technology and diversity analysis methods.The main results were as follows:1.The monitoring results showed that the nutrient state was poor or medium nutrient state.The water quality was good overall,and the influence of human disturbance on water quality was great.The planktonic eukaryotes in Danjiangkou Reservoir were composed of30 phyla,51 classes,73 orders,87 families,101 genera and 121 species.Cryptomonadales was the dominant taxa of planktonic eukaryotes in the reservoir.The abundance and diversity of planktonic eukaryotes in Danjiangkou Reservoir were high.Water temperature(WT),biochemical oxygen demand(COD)and nitrate nitrogen(NO₃^--N)significantly affected the community abundance,while NO₃^--N and transparency(SD)significantly affected the community diversity.The seasonal variation of community similarity was obvious,and the spatial distribution had a certain influence on the composition of planktonic eukaryotic community in Danjiangkou Reservoir.Redundancy analysis(RDA)showed that WT,SD,dissolved oxygen(DO),REDOX potential(ORP),permanganese index(COD_Mn),total phosphorus(TP)and NO₃^--N were significant factors affecting the distribution of phytoplankton eukaryotic community in 2018 and 2019.2.Network analysis of planktonic eukaryotes in Danjiangkou Reservoir showed that the network connectivity in spring was higher than that in autumn.Ascomycota(OTU567),Ciliophora(OTU344)and NO₃^--N,DO,WT were important network center nodes in spring network.Ciliophora(OTU47,OTU1005),Cryptomonadales(OTU239,OTU347),Kathablepharidae(OTU646),Unclassified Eukaryota(OTU678),and Cond,DO,COD,were the important center nodes of the network in the autumn network.DO and Ciliophor,were important network nodes for both the spring and autumn.It played an important role in the environment-taxa interaction of planktonic eukaryotic community in Danjiangkou Reservoir.4.Key taxa in a community played an important role in community structure composition.The weakening or disappearance of key taxa in a community had a significant impact on community structure.The results of random forest analysis and AUC verification showed that eight taxa(Porifera,Cryptomonadales,Unclassified Eukaryota,Norank Eukaryota,Unclassified Cryptophyceae,Ichthyosporea,Cathablepharidae,and Cercozoa)were important taxa of the plankton euaryotic community composition of Danjiangkou Reservoir in 2018 and 2019.It played a crucial role in community composition.5.Functional prediction and metabolic pathway analysis of Picrust 2 showed that the planktonic eukaryotes in Danjiangkou Reservoir were mainly involved in 10 functions(Adenosinetriphosphatase,Peptidylprolyl isomerase,DNA-directed RNA polymerase,DNA-directed DNA polymerase,Proteasome endopeptidase complex,H(+)-transporting two-sector ATPase,Protein-serine/threonine phosphatase,Exo-alpha-sialidase,Histone acetyltransferase,1-alkyl-2-acetylglycerophosphocholine esterase)and 6 metabolic pathways(aerobic respiration I(cytochrome c)),aerobic respiration II(cytochrome c)(yeast),phytol degradation,nicotine degradation IV,fatty acidβ-oxidation II(peroxisome),fatty acidβ-oxidation(peroxisome,yeast).The change of functional abundance in autumn was greater than that in spring,and the change of functional abundance in 2019 was greater than that in 2018.The difference of metabolic pathway niche was that the change of sampling points was greater than the interannual change,and the interannual change was greater than the seasonal change.They showed diversity in functional and metabolic pathways.