Spatiotemporal Variation Of Phytoplankton And Bacterioplankton Communities And Their Relationship With Environmental Factors In Fuxian Lake

The deterioration of water quality is one of the main constraints on the lake ecosystem health.With the intensification of human activities and climate change,a series of environmental problems caused by the increase in nutrients in lakes have been aggravated,and lake water environment has been seriously threatened.As the second deepest lake in China,Fuxian Lake is the 8th and 3rd in the country in terms of lake area and water storage capacity.It stores 9% of China's strategic freshwater resources and provides an important guarantee for the sustainable economic and social development in central Yunnan.In recent years,some studies showed that the water quality of Fuxian Lake has deteriorated,posing a long-term potential damage to the health of the lake ecosystem and the sustainable development of society and economy.Microorganisms can respond quickly to environmental changes due to their short growth cycle.As important components of the lake food web,microorganisms play vital roles in maintaining the health and stability of lake ecosystems,and become common indicators of water environment and ecosystem health.Existing studies have found that the biomass and community structure of phytoplankton in Fuxian Lake have changed significantly in the past few decades,and preliminary research has been conducted on the community composition of bacterioplankton.However,there has been a lack of research on the annual changes of phytoplankton structure,the seasonal variation of bacterioplankton and understanding of the relationship between phytoplankton and bacterioplankton in Fuxian Lake.In this study,we collected phytoplankton in Fuxian Lake from January to December 2015,March,June,September,December in 2016-2018 and bacterioplankton from January to December 2015 periodically.We analysed the spatiotemporal variations of phytoplankton and bacterioplankton communities and their relationship with environmental factors,and further explored their interrelationships.The results will provide an important scientific support for theprotection of Fuxian Lake.The results showed that:(1)A total of 58 genera belonging to 6 phyla of phytoplankton were identified in Fuxian Lake.Chlorophyta was the largest(30 genera),followed by Cyanophyta and Bacillariophyta(11 genera).The number of other phylums was small(3 genera of Pyrrophyta,2 genera of Cryptophyta,1 genera of Chrysophyta).Compared with the absolute dominance of Mougeotia sp.From 2002 to 2003,the dominant species of Fuxian Lake changed significantly.From 2015 to 2016,the dominant species were Ceratium hirundinella,Mougeotia sp.,Cyclotella spp.and Dinobryon spp..From2017 to 2018,the dominant species were Ceratium hirundinella,Mougeotia sp.and Peridinium sp..During the study period,the relative proportion of Aphanocapsa sp.increased.(2)The phytoplankton was composed of Chlorophyta,Pyrrophyta,Chrysophyta,Bacillariophyta,Cyanophyta and Cryptophyta.The proportion of Chlorophyta and Pyrrophyta was higher.The phytoplankton biomass and community structure of Fuxian Lake had obvious trends in time,but the spatial changes were not significant.The total biomass of phytoplankton,the biomass and proportion of Cyanophyta and Pyrrophyta all showed an upward trend year by year,and Chrysophyta biomass increased,but the relative biomass decreased.There were strong temporal variations in biomass and community structure but no significant spatial fluctuations was observed.Redundancy Analysis showed that water temperature,nutrients(total phosphorus,total nitrogen),and ion concentrations(potassium,calcium,sodium and magnesium)were significant factors in driving phytoplankton community structure,in accounting for 8.1%,4.5% and 16.8% of the total variance independently with a shared portion of 1.0%.The coupling of temperature and nutrients,nutrients and ion concentrations,temperature and ion concentrations explained 4.3%,0.1% and 4.2%,respectively.(3)In 2015,bacterioplankton were mainly composed of Actinobacteria,Proteobacteria,Bacteroidetes,Cyanobacteria,Verrucomicrobia,Chloroflexi and Firmicutes in Fuxian Lake.The proportion of Actinobacteria and Proteobacteria was relatively high.The abundance and community structure showed significant changes over time rather than over space.The abundance of bacterioplankton was higher insummer and autumn.Redundancy Analysis displayed that water temperature,nutrients(total phosphorus),phytoplankton biomass and community structure drived the phytoplankton community changes significantly.The water temperature,the total phosphorus and phytoplankton explained 1.3%,5.3% and 14.3% of the bacterioplankton community change independently.The coupling of water temperature and phytoplankton,total phosphorus and phytoplankton explained12.0% and 6.0%,respectively.Water temperature,total phosphorus and phytoplankton jointly explained 0.3%.(4)The Pearson correlation analysis showed that Mougeotia sp.was significantly and positively related to Phycisphaera,Limisphaera and Opitutus,and was significantly and negatively related to Ilumatobacter,Micropruina and Bellinena.Ulothrix sp.was significantly and positively correlated to Terracoccus,Betaproteobacteria and Gimesia,and was significantly and negatively related to Ilumatobacter.Aphanocapsa sp.was significantly and positively related to Micropruina,Betaproteobacteria,Gammaproteobacteria,Thermogutta,Singulisphaera,Pirellula,Aquisphaera and Exiguobacterium,and was significantly and negatively correlated to Actinobacteria unclassified and Sediminibacterium.Cyclotella spp.was significantly and positively correlated to Alphaproteobacteria and Betaproteobacteria.Fragilaria spp.was significantly and positively related to Actinobacteria unclassified,Betaproteobacteria,Gammaproteobacteria,Sediminibacterium,Phycisphaera,Tepidisphaera,Bellilinea.Ceratium sp.was significantly and positively correlated to Alphaproteobacteria,Betaproteobacteria and Haliscomenobacter,and was significantly and negatively related to Ilumatobacter,Micropruina,Ornithobacterium,Bellilinea.Peridinium sp.was significantly and positively related to Alphaproteobacteria,Gammaproteobacteria,Haliscomenobacter,Thermogutta,Pirellula and Aquisphaera,and was significantly negatively related to Betaproteobacteria and Sediminibacterium.Dinobryon spp.was significantly and positively related to Terracoccus,Alphaproteobacteria,Pseudarcicella,Flavobacterium,Haliscomenobacter,Mangroviflexus,Phycisphaera,Gimesia,Limisphaera and Subdivision3_genera_incertae_sedis,and was significantly and negatively correlated to Micropruina,Gammaproteobacteria andBellilinea.