Responses Of Microbial Communities To Environmental Changes In The Middle And Lower Reaches Of The Yangtze River And Lakes In Northern China

Global environmental change is profoundly affecting lake ecosystem.As an important member of lake ecosystem,microbes can perceive the changes of the surrounding environment keenly and respond to them quickly.Therefore,the study of lake microbial response to environmental change is not only conducive to the construction of a complete aquatic ecological system,but also can provide theoretical guidance for coping with a series of ecological problems that may be caused by global environmental change.Here,we studied microbial communities from water and sediments of Tai Lake,lakes in the middle and lower reaches of the Yangtze River and four lakes in northern China,respectively,and investigated the community composition and diversity,their driving factors to achieve more scientific and effective lake environmental management.The main results are as follows:（1）There was obvious spatial environmental heterogeneity in water and sediments of Tai Lake and the Meiliang Bay area showed higher contents of nutrients(loss on ignition（LOI）of sediment,colored dissolved organic matter（c DOM）and phosphate ion(PO₄^3-)of water)and heavy metal elements（Cu,Zn,Ni,Cr）.In the two habitats,the bacterial richness in the northwest area of Tai Lake was relatively high,and the community structure showed significant regional differences.For bacterial communities in lake water,the important factors affecting community richness were water conductivity,p H,sediment porosity and PC1（the first axis of principal component analysis for 12 heavy metal elements）,while the important factors affecting community uniqueness were PC1,water temperature and p H.In addition,the network complexity increased significantly with the increasing p H.For bacterial communities in sediment,the important factors affecting community richness and community uniqueness were the content of total phosphorus,Li and PC2（the second axis of principal component analysis for 12 heavy metals）.Besides,the network complexity decreased with the increasing metallic elements such as Pb,Al and Co,while increased with the increase of phosphorus,total phosphorus,PO₄^3-and ammonia nitrogen（NH₄⁺）in the sediment.（2）In the middle and lower reaches of the Yangtze River Basin with larger spatial scales,eutrophication generally led to significant changes in lake physicochemical factors and caused biotic homogenization of bacterial and fungal communities in both habitats.In the two habitats,community dissimilarities were positively correlated with TSI changes for both taxonomic groups,while the local contribution to beta diversity（LCBD）remarkably declined with increasing TSI for the fungal community.In addition,we found that physicochemical factors such as water temperature and p H were also important for beta diversity of bacterial and fungal communities in water,while heavy metal elements were important for those in sediments.Generalist species,rather than specialist species,were revealed to more dominantly affect the variations in beta diversity along the trophic gradient and contributed more to biotic homogenization.Furthermore,with the increase of eutrophication,the complexity of bacterial network in lake water and sediment decreased,and the complexity of fungal network increased.（3）There were significant environmental differences among Xingkai Lake,Bosten Lake,Hulun Lake and Qinghai Lake in northern China under relatively cold and dry climate.There were the lowest salinity and the highest contents of total phosphorus（TP）in water and nitrate ion（NO₃^-）,nitrite（NO₂^-）,Cr and Co in sediment in Xingkai Lake,while the highest contents of total carbon（TC）,total nitrogen（TN）,dissolved organic carbon（DOC）,NH₄⁺and PO₄^3-in sediments were in Bosten Lake.The contents of TN in water and TP,DOC,NO₃^-,PO₄^3-,Fe,Mn,Zn and Mo in sediments in Hulun Lake were highest,while the contents of salinity and heavy metals Ni,Cu,As,Mo,Cd and Pb in Qinghai Lake were the highest.In addition,for bacterial and fungal communities in Xingkai Lake,the alpha diversity（richness,evenness,Shannon and Chao1）were higher and the local contribution to beta diversity（LCBD）was the lowest.For bacterial community composition and structure,the most important driving factors were salinity and TN in sediment in Xingkai Lake,Cu,Mo and Tl in Bosten Lake,As,redox potential and Ti in Hulun Lake,and Mo and Na in Qinghai Lake.For fungal community composition and structure,the strongest driving factors were salinity and TN in sediments in Xingkai Lake,Tl and Cu in Bosten Lake,the contents of As,NH₄⁺,Ti and NO₃^-in sediments in Hulun Lake,and Tl and Sb in Qinghai Lake.Finally,ecological network analysis revealed the important effects of eutrophication and heavy metal pollution on the microbial networks structure and pointed out the more complex microbial network structure in Xingkai Lake.