| In recent years,affected by climate change and human activities,lake ecosystems are facing a series of ecological problems,such as area shrinkage,hydrological rhythm changes,and biodiversity reduction,which limit the ecological functions of lakes.As an important component of lake ecosystems,microorganisms play an important role in maintaining the stability and ecological function of lake ecosystems.Revealing the main factors affecting the distribution pattern of microbial diversity and regulating the community diversity is the key to predict the response of ecosystems to environmental changes.However,the ecological mechanism that regulates long-term changes in bacterial communities in lake ecosystems is still poorly understood.Based on this,this study took Poyang Lake,the largest freshwater lake in China,as the research object,The 16 S r RNA gene sequencing data of the bacterial community in the water and sediment of Poyang Lake from 2014 to 2021 were obtained by collecting our lab monitoring data in the past years,retrieving the NCBI database,and sampling in situ.The spatial and temporal dynamics of bacterial communities in water and sediment and their influencing factors were analyzed,and the relative contributions of deterministic and stochastic processes to the bacterial community assembly were initially explored.The main conclusions of this study are as follows:(1)The meteorological and hydrological conditions in the Poyang Lake region have changed from 2010 to 2021.The mean annual temperature(0.25 °C/decade),spring temperature(1.5 °C/decade)and winter temperature(2.1 °C/decade)of the region increased significantly,among which the rising rate of winter temperature was the fastest and played the main contribution to the rise of mean annual temperature in Poyang Lake region.The annual average surface wind speed showed a decreasing trend,while the annual precipitation and the mean annual water level did not change significantly.(2)The physicochemical properties of both water and sediments in Poyang Lake showed strong spatiotemporal heterogeneity.The concentrations of total phosphorus,total organic carbon and nitrate nitrogen in water showed a trend of gradual increase from 2014 to 2021,while the total nitrogen and ammonia nitrogen content showed a trend of decrease.The concentration of total phosphorus in the sediments increased gradually from 2014 to 2021,while the total nitrogen,ammonia nitrogen and nitrate nitrogen showed a decreasing trend.(3)The bacterial community structure and assembly process in the water of Poyang Lake showed a significant spatiotemporal heterogeneity from 2014 to 2021.The bacterial community in the water was mainly composed of Proteobacteria(47.5%),Actinobacteria(25%),Bacteroidetes(10.9%)and Cyanobacteria(6.2%).Affected by total nitrogen,total organic carbon and p H,the diversity of bacterial community in the water showed significant differences across time and space.The alpha diversity of the community showed a trend of increasing first and then decreasing over time,reaching the maximum in 2018.By seasonal variation,the bacterial community alpha diversity was highest in spring and lowest in summer.In terms of spatial distribution,the alpha diversity of the community also showed significant differences in different lake areas,with the highest alpha diversity in the estuary region compared with the north lake,south lake reg and sub lake region.The bacterial community structure in the water was significantly affected by the monthly average temperature and water level.Seasonal variation had a stronger effect on bacterial community structure than sampling years and regions.The results of the null model analysis showed that the deterministic process dominated the bacterial community assemble process in the water,with the largest relative contribution from homogeneous selection.I In addition,to explore the effect of temperature on bacterial community,samples were divided into three groups according to temperature: less than 15 °C,15-25 °C and more than 25 °C.The results showed that temperature significantly influences bacterial community diversity,community assembly,and species interactions.With the increase of temperature,the relative abundance of Cyanobacteria increased significantly,while the abundance of Bacteroidetes decreased significantly.Lefse analysis further revealed that Bacteroidetes,Acidobacteria and Cyanobacteria were important indicator groups of less than 15 °C,15-25 °C and above 25 °C groups,respectively.The complexity of microbial cooccurrence network was the lowest at less than 15 °C and the highest at above 25 °C.The contribution of stochastic processes to microbial community assembly was highest at 15-25 °C.(4)The bacterial community structure and assembly process in the sediment of Poyang Lake showed significant spatial and temporal heterogeneity from 2014 to2021.Proteobacteria(32.3%),Acidobacteria(16.4%),Bacteroidota(8%)and Chloroflexi(5.8%)were the most dominant phylum in sediment.Influenced by annual precipitation,mean annual temperature and total nitrogen,the alpha diversity of sediment bacterial communities showed significant differences across time and space.With the change of sampling years,the α-diversity of sediment bacterial communities showed an increasing trend followed by a decreasing trend.In terms of spatial distribution,the alpha-diversity of bacterial communities in the estuary region was significantly higher than the north lake,south lake and sub lake.p H and total nitrogen were the main environmental factors affecting the bacterial community in sediments,while sampling years,seasons and regions had little influence on the bacterial community structure in sediments.In addition,sediment bacterial communities exhibited significant distance decay patterns.The results of the nullmodel analysis indicated that deterministic processes dominated the community assembly of sediment bacteria,and variable selection progress had the greatest relative contribution.Mean annual temperature and annual precipitation significantly affected the balance between deterministic and stochastic processes in sediment community assembly.(5)There were significant differences between water and sediment bacterial community structure of Poyang Lake.Compared with sediment,water bacterial community had lower alpha-diversity and higher beta-diversity.Proteobacteria was the most abundant bacteria both in water and sediment.However,Actinobacteria,Bacteroidetes and Cyanobacteria were more abundant in water bacterial community,while Acidobacteria,Chloroflexi and Verrucomicrobiota were more abundant in sediment.The results of FAPROTAX function predictions showed that bacterial communities in sediments showed higher potential for chemoheterotrophic,hydrocarbon degradation and nitrogen cycling functions,while phototrophic and aerobic heterotrophic functions in water bodies were more abundant.In conclusion,the bacterial community structure and assembly process in the water and sediment of Poyang Lake changed significantly from 2014 to 2021,and temperature was an important factor affecting the bacterial community structure and assembly process in water.These results expand our understanding of the spatial and temporal dynamics,assembly processes and driving factors of bacterial communities in lake ecosystems,and provide clues to the underlying mechanisms of bacterial community succession. |
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