Identification Of Biogeographic And Driving Factors Of Phytoplankton In Plateau Lakes Of Yunnan

Lakes are important components of terrestrial freshwater resources,which provide important water resources and ecosystem services for the development of human society,economy,and culture.The Yunnan-Guizhou plateau is one of the five great lake districts in China with a large number of lakes.The water environment characteristics of plateau lakes differ greatly due to the complex geological and geomorphological differences.Some lakes in Yunnan have been affected to climate change and river basin development in recent decades,the problems of lake reservoirization,eutrophication,and alien species invasion,the health and environmental function of lake ecosystems have been seriously threatened.Phytoplankton,as an important primary producer,is the foundation of the lake food web,which can respond quickly to changes in the water environment,so it is a common indicator of these changes.Exploring the biogeographic model of phytoplankton and driving factors is thus beneficial to understanding the structure and function of aquatic ecosystems.At present,research on the biogeographic distribution of phytoplankton in lakes of Yunnan focuses primarily on the rainy season,with little focus on the geographical distribution pattern in the dry season and seasonal comparison.It is necessary to expand research into the spatiotemporal distribution pattern of phytoplankton in various lake environments.The phytoplankton in 45 lakes of Yunnan were studied in the dry and rainy seasons,and the characteristics of phytoplankton community structure,biomass,and diversity in the two seasons were mainly studied.The driving factors of phytoplankton spatial and temporal distribution were identified using statistical methods such as PCA,RDA,CA,CCA,ANOSIM,T-Text,and multiple regression.The findings may provide a scientific foundation for risk assessment,lake restoration,and biodiversity protection in Yunnan plateau.The main findings are as follows:(1)The water environment factors of 45 lakes in Yunnan had significant differences between rainy and dry seasons in water temperature,dissolved oxygen,p H,total phosphorus andnitrate nitrogen(t test;P<0.05).Total nitrogen,soluble orthophosphate,nitrite nitrogen andchlorophyll,did not differ significantly between rainy and dry seasons(t test;P>0.05).Most physical and chemical indexes have spatial differences,and the distance attenuation of water quality varies by season,with the dry season having a greater change range than the rainy season.(2)During the sampling period from July 2017 to April 2018,82 genera of phytoplankton were identified in 45 lakes in Yunnan,including 35 Chlorophyta genera,22 Bacillariophyta genera,17 Cyanophyta genera,4 Dinophyta genera,2Euglenophyta genera,2 Cryptophyta genera,and 1 Chrysophyta genera.In terms of spatial change,the proportion of diatoms gradually decreased from Laojunshan to Northwest Yunnan to Southeast Yunnan during the rainy season,while the proportion of cyanophyta increased.The benefits of Bacillariophyta decreased during the dry season,but the benefits of cyanophyta and dinoflagellates increased,and the proportion of chlorophyta increased first and then decreased.The changes in phytoplankton community structure in 45 lakes were being driven by nutritional and spatial factors.At the phylum level,the driving effect of nutrients in the rainy season was greater than the spatial difference,while the spatial difference had a greater influence in the dry season.Spatial differences had a greater influence on the community structure of the two seasons than nutrients at the genus level,and spatial distance had a greater influence on the dry season than the rainy season.The influence of nutrition level was greater during the rainy season than during the dry season.(3)The seasonal variation of biomass is generally not significant(t-test;P>0.05).The biomass of Dali West Lake,Erhai Lake,Haixi Lake,Hunshui Sea,Shudu Lake,Yongshengcheng Sea,Changqiao Lake,Dasongshuba,Datun Lake,Dianchi Lake,Qilu Lake,Wenhai Lake,Yuxian Lake,and Yangzonghai varies significantly by season(t test;P<0.05).The spatial distribution trend of phytoplankton biomass was southeast Yunnan > Laojun Mountain > northwest Yunnan.In rainy season,with the increase of nutrition level,biomass first increased and then decreased.The distribution trend of biomass in dry season was increasing with the increase of nutrition level.The results of multiple regression showed that total phosphorus and water temperature were the environmental factors driving the biomass in rainy season.The significant factors driving phytoplankton biomass in dry season are rainfall,total nitrogen and water temperature.(4)There was no significant seasonal difference in α diversity(t test;P>0.05).Spatially,the Shannon wiener index and evenness of phytoplankton at the genus level were Laojun Mountain>Northwest Yunnan>Southeast Yunnan,and the genus level richness was Southeast Yunnan>Northwest Yunnan>Laojun Mountain.Nutrients,water temperature and transparency were the main environmental factors affecting αdiversity in rainy season,and the main driving factors in dry season were water temperature and transparency.The driving effect of nutrients on phytoplankton wasmore visible in the rainy season than in the dry season.There was a significant distance attenuation relationship between the similarity of the rainy and dry seasons,but the dry season trend was more obvious than the rainy season trend.