Spatial-Temporal Variations of Bacterioplankton Community Assemblages and Functional Attributes in the Beibu Gulf, Northern South China Sea

This study used amplicon sequencing of the 16S rRNA gene to explore the community composition and functional attributes of inshore and offshore bacterioplankton in the Beibu Gulf during summer and winter. Results showed a spatial and temporal variation that the inshore and offshore waters in both seasons were significantly different from each other (P<0.05). The abundance of bacterioplankton in summer was higher than winter, with a trend toward higher abundance in inshore than in the offshore. Candidatus Actinomarina, and Synechococcus were the dominant genera between inshore and offshore waters in both seasons. The richness and diversity of bacterioplankton in inshore waters were higher than in offshore waters, and were significantly higher in winter than in summer (P<0.05). The bacterioplankton community was affected by temperature and pH in inshore waters during summer. The dissolved inorganic nitrogen, nitrate, nitrite, and dissolved oxygen affected the inshore waters in winter. We found the bacterioplankton community and structure in inshore waters were mainly affected by West-Guangdong coastal current water mass and terrigenous factors in winter, and affected by terrigenous factors in summer. The Tax4Fun functional abundance analysis showed that the overall functional profiles of the bacterioplankton community in inshore and offshore waters were similar on level 1, but some main functional genes were significantly different at levels 2 and 3. These research findings have provided valuable insights into the crucial roles of bacterioplankton in the ecosystem and its biogeochemical cycles in the Beibu Gulf.