Response of sediment microbial community composition and function to mangrove restoration from an aquaculture pond in...

Mangrove ecosystems, as highly sensitive and productive habitats, host diverse microbial communities essential to biogeochemical cycling. In recent years, large-scale mangrove restoration in former aquaculture ponds has expanded rapidly in China. This represents a typical land-use shift that likely reshapes microbial communities. However, despite its increasing implementation, the accompanying changes in microbial composition and function remain insufficiently understood. Therefore, we compared sediment microbial community composition, diversity, and functional potential between mangrove-planted and reference areas. By absolute-quantification sequencing and metagenomics, we aimed to assess how mangrove restoration regulates the microbial dynamics and their metabolic potentials for carbon, sulfur, and nitrogen cycling after two years of restoration. Mangrove restoration induced a marked phylum shift from Chloroflexota to Pseudomonadota and significantly increased microbial β-diversity (p < 0.05), reflecting enhanced phylogenetic niche differentiation. Specialist species in restored sediments were predominantly Pseudomonadota (e.g., Gammaproteobacteria), contrasting with the Chloroflexota- and Actinobacteriota-dominated reference sites. Functional analysis revealed significant up-regulation of genes involved in polysaccharide metabolism (celB/chbC, sacB, treC, fruB; p < 0.05), assimilatory sulfate reduction, sulfur oxidation (soxZ; p < 0.05), nitrogen fixation (nifH; p < 0.05), and assimilatory nitrate reduction. Furthermore, most high-abundance metagenome-assembled genomes (MAGs) from mangrove sediments encoded sulfate reduction genes. Notably, microbial carbon cycling potential correlated with particulate organic nitrogen, while nitrate concentration linked to nitrogen and sulfur cycling genes, highlighting cross-element synergies. These findings demonstrated that two years of mangrove restoration alters sediment microbiomes and their biogeochemical functions potential, thereby may influence carbon sequestration and nutrient cycling in coastal ecosystems.