Spatial Distribution Pattern And Influencing Factors Of Bacterioplankton Communities In The Yuan River

With acceleration of industrialization and urbanization,the spatial pattern of river ecosystems has undergone changes profoundly.The bacterioplankton community is an important indicator reflecting the status of the river ecosystem and its spatial patterns reflect the impact of environmental changes.Understanding the spatial distribution of bacterioplankton community can help us to understand deeply the mechanism of the formation and maintenance of bacterial diversity and predict the evolution direction of river ecosystem function.At present,the interpretation of the spatial distribution of bacterioplankton community is mainly based on the meta-communities theory,namely,species sorting and mass effect.River water chemistry,basin land use types,and spatial geographic distance all are environmental factors that affect the spatial distribution of bacterioplankton communities.The three above are related to the mechanism of species sorting and mass effect.Therefore,this article aims to investigate the effects of water chemistry,land use,and geographic distance parameters on the spatial distribution of bacterioplankton communities and to explore the main mechanisms.We collected surface water samples at 16 sampling sites from the upper reaches of the Yuan River to the downstream in August 2018?wet season?and January 2019?dry season?in this study.Water chemistry parameters(pH,DO,DOC,NH₄⁺-N,TP,NO₃^--N,Cl^-,SO₄^2-,Mn,Fe,Zn,Pb)were detected;percentage of land use types?agriculture,forests,freshwater,imperative land?and geographical distance parameters?river length,catchment area,cumulative dendritic distance,mean dendritic distance?both calculated by ArcGIS.Based on high-throughput sequencing,we analyzed characteristics of bacterioplankton communities.Based on Bray-Curtis distance of bacterioplankton communities,non-metric multidimensional scale analysis and hierarchical clustering analysis both were used to understand the differences of bacterioplankton communities structure among the sampling sites.Based on redundancy analysis,the relationship between environmental factors and bacterioplankton communities were detected.Variance partitioning analysis was used to distinguish the influence of water chemistry,land use and geographic distance quantitatively and to determine the dominant influence mechanism.Our results showed that:?1?The dominant bacterioplankton communities in the Yuan River were Actinobacteria,Proteobacteria,Bacteroidetes,Cyanobacteria and Verrucomicrobia.In the upper reaches,Bacteroidetes was dominant during the wet season.In the middle reaches with a lake/reservoir and in the downstream with Xinyu city,Actinobacteria was dominant,and abundances of Proteobacteria was less than other river sections.Both the abundances of Cyanobacteria and Verrucomicrobia were more in the wet season than in the dry season significantly.?2?Both the diversity index and richness index of bacterioplankton communities varied significantly from the upper stream to the downstream,and the trend was opposite between the wet season and the dry season.In the wet season,the diversity index and richness index of bacterioplankton communities were the lowest in the upper reach and lower than the downstream significantly;while in the dry season,the diversity index and richness index of bacterioplankton communities were the highest in the upper reach,and richness index was higher than the downstream significantly.Both the diversity index and richness index of bacterioplankton communities were significantly higher in the dry season than in the wet season.?3?Water chemistry,land use and geographic distance all had significant influence on spatial distribution of bacterioplankton communities,and the influence of the three were same.In the wet season,the explanation of environmental factors were geographical distance 32.7%,land use 29.0%,water chemistry 27.6%;in the dry season,the explanation of environmental factors were geographical distance 27.9%,land use22.8%,water chemistry 20.1%.In the water chemistry parameter,Mn was the best to explain the variation in bacterioplankton communities;in the land use types,freshwater area was the best to explain the variation in bacterioplankton communities;in the geographic distance parameters,cumulative dendritic distance was the best to explain the variation in bacterioplankton communities.?4?Species sorting mechanism and mass effect mechanism both influence the spatial distribution characteristics of bacterioplankton communities in Yuan River.In the wet,the explanation of species sorting and mass effect were 27.6%and 26.4%respectively that means species sorting and mass effect had same influence mostly.In the dry season,the explanation of species sorting and mass effect were 20.1%and 34.1%respectively that means mass effect was the domination.