Seasonal Variation in Bacterial Community Structures of Mangrove Sediments

Climate change globally and sea level rise affect the mangrove ecosystem. The high diversity and temporal heterogeneity of the mangrove ecosystem will lead to a high diversity of sediment bacterial community structure and function. However, seasonal variations and potential assembly mechanisms of sediment bacterial communities in mangrove ecosystems remain to be discovered. We collected rhizosphere sediments and bulk sediments from Kandelia obovata and Aegiceras corniculatum at three locations covering Dongzhai Harbour in spring, summer, autumn, and winter, and sequenced 16S rRNAs. The results indicated that the alpha and beta diversity of bacterial communities in mangrove sediments differed significantly between seasons, and the bacterial communities in rhizosphere sediments had smaller seasonal changes and were more stable than those in bulk sediment bacterial communities. The seasonal changes in carbon, nitrogen content, and pH were the main influencing factors. The stochastic process dominated the assembly of bacterial communities in mangrove sediments. The assembly of bacterial communities varies between seasons. We found that the proportion of dispersal limitation was significantly negatively correlated with the carbon and nitrogen content in the sediment. Compared with bulk components, the dispersal limitation of bacterial communities in rhizosphere sediments accounted for a lower proportion of community construction, which might be caused by higher carbon and nitrogen content conditions in rhizosphere sediments. We found that beta diversity based on Bray-Curtis distance was significantly positively correlated with dispersal limitation, which explained why the beta diversity of bacterial communities in rhizosphere sediments was significantly lower than that of bulk components. This study increases the understanding of the responses of mangrove bacterial communities to seasonal change and may be beneficial for the protection of mangrove ecosystems in the face of climate change.