Abstract: Mangroves often have well-developed root systems, providing rhizosphere habitats for diverse microorganisms that mediate the elemental cycles in coastal wetlands. However, the extent to how these microbial communities differ across co-occurring mangrove species remains unclear. In this study, we systematically investigated microbial diversity, community composition, and functional potential in rhizosphere sediments of five mangrove species and adjacent unvegetated mudflats within a single mangrove ecosystem across six sampling time points from May 2019 to December 2020. Amplicon sequencing revealed that microbial diversity and community composition were temporally stable but differed significantly among mangrove species, with plant identity accounting for over 70% and 60% of the total explained variation in alpha diversity and community composition, respectively. Phylosymbiosis analysis further demonstrated that plant identity structured microbial community composition (PACo, P < 0.01). Metagenomic analysis revealed species-specific functional profiles related to methane, nitrogen, sulfur, and phosphorus cycling exhibited distinct abundance patterns across mangrove rhizospheres and mudflat sediments. Methane-oxidation potential was higher only in Bruguiera gymnorrhiza composites, whereas Avicennia marina composites showed higher relative abundance of methylotrophic and acetoclastic methanogenesis genes. Specifically, assimilatory nitrate reduction and nitrogen fixation pathways tended to be more abundant in mangrove rhizospheres, whereas dissimilatory nitrate reduction and sulfur oxidation pathways were more abundant in mudflats. Our findings underscore the predominant role of plant identity in shaping rhizosphere microbial diversity and metabolic potential, offering novel insights into the potential species-specific contribution of mangroves to coastal elemental cycling.

Key words: Mangrove, Rhizosphere, Microbial diversity, Biogeochemical cycles, Phylosymbiosis