Disentangling The Drivers Of Spatiotemporal Succession Of Phytoplankton From Drinking Water Reservoirs:Insights Into Compositions And Co-occurrence Of Bacterial Communities

With the deepening research of the ecological health assessment and algae bloom mechanisms of lakes and reservoirs,the dynamics of phytoplankton community driven by microbial factors in reservoir increasingly become a hot topic.In reservoir ecosystems,microbes are the critical contributors to primary productivity,and the formation of algal blooms is closely related to the symbiotic microbes.However,the specific bacteria-algae interaction succession and its water quality regulation mechanism are not clear.In this study,two drinking water reservoirs in Xi'an city were utilized as research objects,and high-throughput DNA sequencing and co-occurence network were employed to monitor the seasonal variations in water quality,phytoplankton community,and associated flora structure for one year,thus revealing the driving mechanism of interaction between the phytoplankton community succession and the associated flora in reservoirs.Ultimately,the biological mechanism of water-lifting aerator to inhibit the algal growth was explored from the perspective of intracellular metabolism.The results will provide a scientific basis for the algal bloom mechanism and artificial algae control technology in drinking water reservoirs.The main findings as follows:?1?Taking Jinpen Reservoir as the object,the 18S rDNA high-throughput sequencing and co-occurence network were employed to investigate the ecological interaction between the spatiotemporal succession of phytoplankton community and eukaryotes.The results showed that:1)Bacillariophyta and Chlorophyta were the dominant species.Chrysophyta peaked in April,with a relative abundance of 80.05%.2)DNA sequencing showed that the Ciliophora was the dominant group,reaching a maximum of 95.33%in March.The relative abundance of arthropods in October was 55.20%,and rotifers dominated in May.3)Co-occurrence network indicated that the interaction between algae and eukaryotes was mainly mutualism.As keystone taxa,Symbiodinium and Salpingoeca positively correlated with most algae.Staurastrum as a keystone species was positively related to Lagenidium and Spirostrombidium?P<0.05?.4)Environmental factors explained a total of 88.4%of the algal community and 61.4%of the eukaryotic microbial community variation.NH₄⁺-N,TN and water temperature all significantly affected the succession of algal and eukaryotic communities.?2?Taking Lijiahe Reservoir as the object,the ecological interaction relationship between the spatiotemporal succession of phytoplankton community and bacterial community was studied using 16S rDNA high-throughput sequencing and co-occurence network.The results showed that:1)Bacillariophyta and Chlorophyta were also dominant species.In August,Cyanobacteria replaced Bacillariophyta as the second dominant species,with an average relative abundance of 30.13%.2)DNA sequencing showed that Proteobacteria,Actinobacteria,and Bacteroidetes dominated throughout the year.Proteobacteria reached the maximum relative abundance of 71.68%in July.Acidobacteria and Deinococcus-Thermus as rare taxa reached the maximum relative abundances of 10.20%and 5.56%,respectively.3)Co-occurrence network showed that the association between algae and bacteria was mainly positive.As a keystone species,Methylotenera was significantly positively related to Chlorella?P<0.05?.Scenedesmus was also a keystone species,exhibiting significant negative correlations with various bacteria such as Methylobacter,Solitalea,and Rhodoferax?P<0.05?.4)RDA analysis showed that the interaction between algae and bacterial communities was significantly regulated by water temperature,pH,and conductivity,and environmental factors explained 93.1%and 90%of the algal and bacterial community variation,respectively.?3?The spatiotemporal succession and ecological interactions of algal and eukaryotic communities during the mixed period in Jinpen Reservoir were studied with 18S rDNA high-throughput sequencing and co-occurence network analysis.The results showed that:1)During the winter mixed period,Arthropoda?6.63%to 79.19%?,Ochrophyta?5.60%to35.16%?,Ciliophora?1.81%to 10.93%?,and the Cryptomonadales?0.25%to 11.48%?were the most abundant species in the eukaryotic community.2)Cryptomycota significantly increased with the algal density decreased,indicating that there may be a saprophytic association between Cryptomycota and algae,and the lysis of algae might promote Cryptomycota growth.3)Co-occurrence network showed that Penicillium was significantly negatively correlated with most other algae?P<0.05?,indicating that Penicillium negatively affected the growth of algae,and there may be antagonism,competition or saprophytic association between them.4)TN,NH₄⁺-N,water temperature,DOC,Mn,conductivity,and pH as drivers significantly shaped the succession of algal and eukaryotic communities.?4?Based on field investigation and laboratory simulations,the biological mechanism of water-lifting aerator to inhibit the algal growth was explored from the perspective of intracellular metabolism.The results showed that:1)water temperature and light played a pivotal role in the growth and metabolism of algae.Microcystis aeruginosa reached its maximum in algal density,chlorophyll a,chlorophyll fluorescence parameters,and dehydrogenase activity under light condition at 25?.2)Carbon metabolism profile showed that the metabolic activity of Microcystis aeruginosa reached its maximum under the conditions of 25?and light,and the metabolic activity of Microcystis aeruginosa cultured for 48 h varied significantly under low temperature and light conditions?P<0.01?.3)Three-dimensional fluorescence spectroscopy combined with parallel factor analysis showed that the extracellular and intracellular dissolved organic matter of Microcystis aeruginosa resolved three components.EOM were tyrosine-like,tryptophan-like,and UVA humic-like.IOM were UVC humic-like,UVA humic-like and tyrosine-like.The total fluorescence intensity of EOM and IOM both reached the maximum under the light condition of 25?.4)Water-lifting aerator exhibited significant negative impacts on algae in the Lijiahe and Jinpen reservoirs.The chlorophyll fluorescence parameters significantly reduced after the water-lifting aerator operation,indicating that the operation weakened the photosynthetic ability and destroyed the biological activity of algae.