The Study Of Picoeukaryotic Plankton Diversity In Small Lake Ecosystems Based On Ecological Enclosure

Picoeukaryotic plankton in water ecosystems play the roles of primary producers,consumers,and decomposers in food webs and micro-food chains,and they are quite sensitive to changes in various factors in the water environment.The changes of organisms can play a certain role in indicating the evolution of the water environment.Most of the traditional identification of microorganisms are easily affected by sampling methods,preservation methods,technical operating conditions,etc.,and there are certain errors and disputes.With the development of third-generation sequencing technology,the accuracy and precision of microbial identification have been improved.Affected by natural disturbance and man-made disturbance,the eutrophication state of Qingshan Lake in Huangshi City,Hubei Province has become increasingly serious,and the diversity of plankton in the corresponding water body will also change.In this paper,the Qingshan Lake algal ecosystem was used as the research water area,and two enclosure areas were set up in the main lake area for the transition from grass to algae,and from the intermediate state of grass and algae to algae.Picoeukaryotic plankton were taken as the research object,single-molecule real-time sequencing(SMRT)technology was used to sequence the 18S r DNA V1-V9full-length region in environmental samples.The community composition,richness and diversity of picoeukaryotic plankton in ecosystems of different states,the spatiotemporal heterogeneity between spring and summer,as well as biomarker were studied.To analyze the correlation between dominant species and environmental factors,and finally combined with co-occurrence network,the key species affecting Qingshan Lake and the surrounding ecosystem community were analyzed.The results were as follows:1.Environmental factors and eutrophication:Excessive content of TP,TN and DO were important environmental problems in Qingshan Lake waters.TLI(COD_Mn)and TLI(Chl.a)contributed more to water quality eutrophication.Phosphorus was a nutrient element that limited the type and abundance of algae in the Qingshan Lake spring algal ecosystem,the grass-algae-type ecosystem in enclosure B in spring,and the algal-type ecosystem in enclosure A in summer.Nitrogen and phosphorus co-restricted the grass-type ecosystem of enclosure A in spring,algal ecosystem of enclosure B in summer and Qingshan Lake in summer.Qingshan Lake had the highest degree of eutrophication in summer,followed by Qingshan Lake in spring,enclosure A in summer,enclosure B(with the same degree of eutrophication in spring and summer),and enclosure A in spring.2.Structural characteristics of picoeukaryotic plankton community:The dominant species in spring enclosure A were Halteria grandinella,Cryptomonas pyrenoidifera and Mychonastes homosphaera,with relative abundances of 19.09%,17.28%and 12.17%,respectively.In the spring,between enclosure B and Qingshan Lake,Cryptomonas pyrenoidifera was the absolute dominant species in the community,and the relative abundances accounted for 45.36%and 16.54%,respectively.The dominant species in enclosure A in summer were Cyclotella meneghiniana and Tetracystis tetraspora.The dominant species in enclosure B in summer were Cyclotella meneghiniana,Cryptomonas pyrenoidifera.Cyclotella meneghiniana was the absolute dominant species in Qingshan Lake in summer,and Pseudouroleptus caudatus had a relatively large relative abundance in the community,accounting for 26.18%of the total relative abundance.3.Correlation and spatiotemporal heterogeneity between Alpha diversity and environmental factors:Seasonal differences between spring and summer had a greater impact on the richness and diversity of picoeukaryotic plankton communities than space.Phosphate(PO₄-P)and water temperature(WT)were the main factors affecting the abundance and diversity of picoeukaryotic plankton,meanwhile,the abundance and diversity of picoeukaryotic plankton were also affected by conductivity(SPC)and dissolved oxygen(DO).4.Correlation between picoeukaryotic plankton and environmental factors:WT was significantly positively correlated with Cyclotella meneghiniana,Pseudouroleptus caudatus and Golenkinia longispicula,and significantly negatively correlated with Cryptomonas pyrenoidifera and Halteria grandinella.Chemical Oxygen Demand(KMn O₄,COD_Mn)was positively correlated with Halteria grandinella,Masaia oloidia,Desmodesmus armatus,Tetracystis tetraspora,Lagenidium giganteum,and negatively correlated with Cryptomonas pyrenoidifera,uncultured apicomplexan.5.Biomarker analysis:Choreotrichia sp,Cryptomonas obovoidea and Achlya bisexualis could be used as early warning species for enclosure A grass-type ecosystems in spring.Tetracystis tetraspora,Scenedesmus ovalternus,Nautococcus solutus,Chloromonas oogama,Oogamochlamys zimbabwiensis could be used as early warning species for enclosure A algal-type ecosystems in summer.Golenkinia longispicula,Pseudouroleptus caudatus and Chaetonotus hornsundi could be used as early warning species for enclosure B algal-type ecosystems in summer.Cyclotella meneghiniana,uncultured fungus and Aulacoseira granulata could be used as early warning species for the algal ecosystem of Qingshan Lake in summer.6.Co-occurrence network analysis:Vitreochlamys incisa,Cylindrocapsa geminella,Coleps hirtus,Nautococcus solutus,Monoraphidium dybowskii,and Aulacoseira granulate were the key species in the community,which played important roles in maintaining the community structure stability of the Qingshan Lake and the enclosures in spring and summer.The research results provide data reference and work basis for a more systematic understanding of the community structure of picoeukaryotic plankton in different states of ecosystems,their relationship with environmental factors,their ecological functions,and environmental monitoring.