Assembly Mechanisms Of Bacterioplankton Community Structure And Co-occurrence Network In Urban Lakes

The rapid expansion of urban area and population in China has brought tremendous pressure on regional ecosystems and caused numerous negative impacts on lake ecosystems.The bacterioplankton communities in lakes are highly sensitive to changes in water environmental conditions,and are key biological indicators of environmental stressors triggered by urbanization or climate change,such as warming,metal pollution,and eutrophication.Bacterioplankton can also decompose and transform pollutants into harmless substances for the environment based on biochemical processes such as metabolism,nitrification,and denitrification.They are an essential part of the biogeochemical cycle.This study focuses on the bacterioplankton communities in lakes of Nanchang City,by studying the structure and co-occurrence network of bacterioplankton communities in urban lakes,aiming to reveal the ecological assembly mechanism that drives the spatiotemporal changes in bacterial communities and clarify the regulatory role of community assembly mechanisms on the stability of bacterial networks.The ultimate goal is to improve the relationship between humans and the environment and protect the lake ecosystem in the process of urbanization.The results show that:(1)Significant urban-suburban differences in α-diversity of bacterioplankton communities in lakes of Nanchang City,with not significant seasonal differences.The Chao1 richness and phylogenetic diversity values of bacterial communities in suburban lakes were significantly higher than those in urban lakes,while Shannon diversity did not differ significantly between the two areas.The average values of the three α-diversity indices for bacterial communities in the dry season were higher than those in the wet season,but none of them reached a significant level.(2)The dominant phyla in the bacterial community were Actinobacteria(average relative abundance of 34.3%),Proteobacteria(27.35%),Cyanobacteria(19.26%),and Bacteroidetes(9.37%).The average relative abundance of these dominant phyla did not show significant differences between urban and suburban lakes.However,Actinobacteria and Proteobacteria showed significant seasonal differences in their average relative abundance.The average relative abundance of Actinobacteria was significantly higher in the wet season(41.42%)than in the dry season(27.19%),while the average relative abundance of Proteobacteria was significantly higher in the dry season(30.5%)than in the wet season(24.19%).(3)The structure of bacterioplankton communities showed significant differences between lakes in urban and suburban areas,as well as between different seasons.Rare groups such as Parcubacteria,Nitrospirae,and Ignavibacteriae showed significantly higher average relative abundance in suburban lakes compared to urban lakes.Apart from Actinobacteria and Proteobacteria,rare groups such as Omnitrophica,Elusimicrobia,and Fibrobacteres showed significantly higher average relative abundance in the dry season compared to the wet season.The similarity of bacterial communities in suburban lakes decreased significantly with increasing geographical distance,while this trend was not evident in urban lakes.The similarity of bacterial communities in lakes during wet and dry seasons also decreased significantly with increasing geographical distance,with a significantly higher decrease in the dry season.(4)The impact of environmental selection on the spatiotemporal variation of bacterioplankton communities was greater than that of spatial dispersal.The explanatory power of environmental selection and spatial dispersal on the variation of bacterioplankton communities in urban lakes was 30% and 6%,respectively,and the explanatory power in suburban lakes was 27% and 2%,respectively.In the wet season,the explanatory power of environmental selection and spatial dispersal was 51% and15%,respectively,and the explanatory power in dry season was 46% and 23%,respectively.Ammonia nitrogen was the most important environmental factor causing variation in bacterioplankton communities in urban and suburban lakes.In the wet season,water temperature and ammonia nitrogen were the main environmental factors influencing the bacterial community,while in the dry season p H and dissolved oxygen were the main factors.(5)Deterministic processes dominated the assembly of bacterioplankton communities in the lakes of Nanchang City.The contribution rate of deterministic processes to the assembly of urban and suburban lake communities was 66% and 82%,respectively,while that of stochastic processes was 34% and 18%,respectively.In the wet and dry seasons,the contribution rate of deterministic processes to the assembly of lake communities was 62% and 82%,respectively,while that of stochastic processes was 38% and 18%,respectively.Shannon diversity,ammonia nitrogen,water temperature,and p H were important factors balancing the stochastic and Deterministic processes in regulating bacterial community assembly.As the differences in these regulating factors increase,the bacterial community transitioned from stochastic to deterministic assembly.(6)The complexity and stability of bacterial co-occurrence networks differed significantly between urban-suburban lakes and between seasons.The complexity of the bacterial network in urban lakes was higher than that in suburban lakes,and the complexity in the dry season was higher than that in the wet season.The stability of the bacterial community network in the wet season was significantly higher than that in the dry season,and the stability of the bacterial network in urban lakes was higher than that in suburban lakes,but not at a significant level.(7)The dynamic balance between stochastic and deterministic processes drived changes in the stability of the bacterial network.When the bacterial community assembly was driven by relatively strong stochasticity,the stability of the bacterial network was stronger,while stronger deterministic processes will reduced the stability of the bacterial network.Water temperature was the most important environmental factor affecting the stability of the bacterial network in lakes,and as water temperature continues to rise,the stability of the bacterial network significantly increased.