Abstract: This study focused on the impact of tidal changes on the microbial communities in the rhizosphere and leaves ofZostera japonica. Nanopore amplicon sequencing was used to analyze the diversity, structure, and functional characteristics of the microbial communities of the leaves and rhizospheres across the high tide zone, low tide zone, and subtidal area. Environmental factors were also evaluated to assess their influence on the microbial communities. The results showed that the microbial abundance and diversity of the leaves and rhizosphere was similar to tidal change trends, peaking in low-tide zones and reaching minima in subtidal areas. Tidal variation significantly altered the α-diversity index of the leaf microbiota （P<0.05）, without affecting the rhizosphere microbiota （P>0.05）. In the subtidal and high tide zones, the leaf and rhizosphere microbial communities exhibited a higher abundance of characteristic taxa. In the high tide zone, leaf microbiota adapted to the exposed environment and were involved in sulfur cycling, while in the low tide zone, leaf microbiota showed strong organic matter degradation capacity. In the subtidal zone, leaf microbes not only efficiently degradated organic matter but also participated in nitrogen and sulfur cycling. High-tide rhizosphere microbes prioritized sulfur cycling and redox homeostasis, contrasting with low-tight populations specializing in nitrogen fixation and degradation. The subtidal rhizosphere were adapted to low-oxygen environments and participated in sulfur cycling. Sediment total organic carbon （TOC） significantly affected the composition and distribution of rhizosphere communities. From the high tide zone to the subtidal zone, the rhizosphere microbial ability to utilize organic matter, sulfur compounds, and nitrogen respiratory activity increased, while aerobic heterotrophic activity decreased. Leaf microbiota displayed enhancing nitrate reduction but reducing sulfur respiration and photoautotrophy. These findings provide theoretical support for the conservation strategies ofZ. japonica.

Key words: Zostera japonica, tides, microbial abundance, microbial diversity, environmental gradient