Spatial and temporal dynamics of bacterioplankton community composition in a subtropical dammed karst river of southwestern China

River damming influences the hydro-physicochemical variations in karst water; however, such disruption in bacterioplankton communities has seldom been studied. Here, three sampling sites (city-river section, reservoir area, and outflow area) of the Ca2+-Mg2+-HCO3--SO42- water type in the dammed Liu River were selected to investigate the bacterioplankton community composition as identified by high-throughput 16S rRNA gene sequencing. In the dammed Liu River, thermal regimes have been altered, which has resulted in considerable spatial-temporal differences in total dissolved solids (TDSs), oxidation-reduction potential (Eh), dissolved oxygen (DO), and pH and in a different microenvironment for bacterioplankton. Among the dominant bacterioplankton phyla, Proteobacteria, Actinobacteria, Bacteroidetes, and Cyanobacteria account for 38.99%-87.24%, 3.75%-36.55%, 4.77%-38.90%, and 0%-14.44% of the total reads (mean relative frequency), respectively. Bacterioplankton communities are dominated by Brevundimonas, Novosphingobium, Zymomonas, the Actinobacteria hgcIclade, the CL500-29 marine group, Sediminibacterium, Flavobacterium, Pseudarcicella, Cloacibacterium, and Prochlorococcus. Their abundances covary with spatial-temporal variations in hydro-physicochemical factors, as also demonstrated by beta diversity analyses. In addition, temperature plays a pivotal role in maintaining bacterioplankton biodiversity and hydro-physicochemical variations. This result also highlights the concept that ecological niches for aquatic bacteria in dammed karst rivers do not accidentally occur but are the result of a suite of environmental forces. In addition, bacterioplankton can alter the aquatic carbon/nitrogen cycle and contribute to karst river metabolism.