Structural characteristics of microbial communities in typical tropical offshore rivers and their carbon,nitrogen,and phosphorus cycling characteristics and mechanisms
Estuarine rivers played a crucial role in studying the physical,chemical,biological,and geological processes between land and sea,as well as their interactions,global environmental changes,and the impacts of human activities.This study focused on the West River in Sanya City,a typical tropical estuarine river.The eDNA metabarcoding and qPCR functional gene array technologies were applied to analyze the diversity,structural composition,interaction relationships,and assembly processes of planktonic bacterial communities,as well as the abundance of 71 genes related to(C)carbon,(N)nitrogen,(P)phosphorus,and(S)sulfur cycling across 13 surface water sampling sites in the upper,middle,and lower reaches of the river.Our results revealed significant differences in bacterial community diversity,structure,interaction relationships,and assembly processes among different river sections.Bacterial diversity decreased in the lower estuarine region,with increased environmental heterogeneity and distinct community structures between river segments.Environmental heterogeneity was heightened in the middle reach,where freshwater and saltwater mix,leading to a more complex microbial co-occurrence network,with deterministic processes dominating community dispersal.Furthermore,functional analysis of the planktonic bacteria indicated that the expression of most microbially mediated genes involved in C,N,and P cycling was suppressed in the downstream areas.Random Forest analysis suggested that Verrucomicrobia and Tenericutes might be the most important functional groups involved in C,N,and P cycling.Redundancy Analysis(RDA),Hierarchical Partitioning(HP),and Mantel tests indicated that salinity gradients caused by saltwater intrusion are one of the key mechanisms regulating the planktonic bacterial community and the biogeochemical cycling of C,N,and P.These findings enhanced our understanding of the compositional characteristics of estuarine river bacterial communities and clarified their role in riverine and marine biogeochemical cycles.This research provided a theoretical foundation for monitoring,assessing,and improving water quality,aquatic environments,and the health and safety of aquatic ecosystems.
bacterioplanktonSanya West Riverbiogeochemical cyclingfunctional genesfreshwater salinisation
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