Homogeneous selection is not always important in bacterial community in the eutrophic enclosed bay

Abstract

Abstract Background Previous studies have found that coastal eutrophication increases the influence of homogeneous selection on bacterial community assembly. However, whether seasonal changes affect the dominance of homogenous selection in bacterial community assembly in eutrophic bays remains unclear. Sansha Bay is an enclosed bay with ongoing eutrophication, located in the southeast coast of China. We investigated the bacterial community composition at two depths of the enclosed bay across seasons and the seasonal variation in community assembly processes. Results Diversity analyses revealed that the bacterial community composition among seasons differed significantly. By contrast, there was little difference in the community composition between the two depths. The temperature was the key environmental factor influencing the community composition. The null model indicated that the relative importance of homogeneous selection decreased in the following order: spring > winter > autumn > summer. Homogeneous selection did not always dominate the community assembly among seasons in the eutrophic bay. The effects of pure spatial variables on the community assembly were prominent in autumn and winter. Conclusions Our results showed the seasonal influence of eutrophication on bacterial community diversity. The seasonal variation in composition and structure of bacterial communities eclipsed the vertical variability. Eutrophication could enhance the importance of homogeneous selection in the assembly processes, but the seasonal environmental differences interfered with the steady-state maintained by ongoing eutrophication and changed the community assembly processes. Homogeneous selection was not always important in bacterial community in the eutrophic enclosed bay. The bacterial community was the most complex in summer, because the composition differed from other seasons, and the assembly process was the most intricate. These findings have contributed to understanding bacterial community composition and assembly processes in eutrophic coastal ecosystems.