Seawater tides shaped mangrove sediment a bacterial community drastically distinct from supratidal land soil.

The intertidal zone where mangroves inhabit is unique for both plants and microbes. The periodic seawater tides have allowed only a very small portion of woody plants to shift as mangroves. However, the understanding of how seawater tides shape bacterial community in mangrove sediment is not yet comprehensive. By comparing mangrove sediment in low-tidal zones to land soil in supratidal zones, we investigated their differentiation of bacterial community in diversity, composition, interaction and functional potential, assembly mechanisms, and the underlying factors. Using 16 S ribosomal RNA (rRNA) gene sequencing, we found drastic distinctness in community composition and structure between these two types of soils. The distinctness was partially attributed to the high level of dispersal limitation in assembling processes and strongly correlated with the differences of sea tide-related edaphic conditions, including moisture, total carbon, total sulfur, salinity, and pH. The periodic inundation in mangrove sediment has also shaped a more complex and compact bacterial interaction network, and strong dispersal limitation between low-tidal and supratidal zones. With supratidal soil as the control, our findings highlight the direct influence of sea tides on bacterial community in mangrove sediments, providing support for employing microbes as early indicators of biological community change in coastal zones upon the projected sea-level rise.