Biogeographic Distribution And Driving Factors Of Free-living And Particle-attached Bacterial Communities In The Yellow River

Bacteria are important in river ecosystem,which plays an important role in regulating biogeochemical cycles and maintaining ecosystem functions.Studying the spatial distribution pattern and causes of bacteria will help us to conduct reasonable management and functional regulation of river ecosystems.As the second largest river in China,the Yellow River is the most important water source in Northwest and North China.It has a unique freshwater river ecosystem.Under such specific physical geographical conditions,the biogeographic distribution of its bacterial community and its driving factors may have their particularity.However,there are currently no reports on the research of the entire Yellow River basin.In this study,the bacteria survey was carried out in the whole reach of the Yellow River in April-May and Sept-October 2019.A total of 45 typical river reaches of the main stream were selected to reveal the community succession patterns of free-living and particle-attached bacteria in the background of sandy river.The main results are as follows:(1)The diversity and biogeographic distribution of free-living bacteria in the Yellow River.The ? diversity index of free-living bacteria was positively correlated with turbidity(Turb),total phosphorus(TP),total dissolved phosphorus(TDP)and total suspended solids(TSS).Seasonally,there was no significant difference in Shannon index.From different regions,there is a significant difference in spring.The free-living bacterial communities had a strong distance-decay patterns in both seasons.But the rate of change is different in the two seasons,and the rate of change in spring is higher than that in autumn.Mantel and Partial Mantel tests showed that water environmental parameters were more important than geographical distance in building microbial communities in both seasons.(2)The diversity and biogeographic distribution of partical-attached bacterial to the Yellow River.There were significant seasonal and spatial differences in the attachment bacterial community,and the partical-attached bacterial community showed a strong distance attenuation pattern in the two seasons,indicating that the spatial pattern was basically the same under different hydrological conditions.Mantel and partial Mantel tests showed that environmental factors and spatial factors were significantly related to the variation of the attached bacterial community,and spatial factors had a higher influence on the construction of bacterial community in autumn than in spring.NCM results further showed that the neutral theoretical model had a better fit degree in autumn.(3)The composition and driving factors of free-living and partical-attached bacterial communities in the Yellow River.Among the two bacterial groups,the three dominant groups were Proteobacteria,Bacteroidetes and Actinobacteria.The a diversity index of free-living bacteria was generally lower than that of particle-attached bacteria.The specific ESV of free-living bacteria was lower than that of particle-attached bacteria,and the proportion of ESV shared in the source region and downstream was relatively low in the two seasons.The Mantel and Partial Mantel tests based on unweighted Unifrac distance showed that environmental factors were dominant in constructing community structure of two bacterial groups.