Mangrove sediments act as important sinks and reactors for phosphorus (P), yet the mechanisms governing depth-dependent microbial P cycling under strong geochemical gradients remain insufficiently understood. Here, we combined metagenomics, sediment geochemistry, and genome-scale metabolic modeling to investigate microbial P cycling strategies across a five-meter mangrove sediment core.
We observed pronounced vertical stratification of P-cycling functional potential, with a general decline in functional gene diversity from surface (≤40 cm) to intermediate depths (40–400 cm), followed by a partial recovery in deeper sediments (>400 cm), despite intensified P limitation and reduced organic carbon availability. This pattern suggests that microbial communities maintain functional resilience in deep sedimentary environments through adaptive metabolic reorganization.
Taxonomic shifts were evident along the depth profile, with surface and intermediate layers enriched in diverse heterotrophic bacterial lineages, whereas deep sediments were characterized by a reduced but functionally specialized community structure. Genome-resolved analyses indicate that multiple taxa contribute to phosphorus acquisition and recycling via complementary strategies, including phosphite oxidation, organic phosphorus mineralization, and iron-bound phosphate mobilization.
Genome-scale metabolic modeling further suggests the presence of metabolically interconnected microbial consortia capable of sustaining phosphorus turnover under resource limitation, potentially mediated through exchange of low-molecular-weight phosphorus compounds and coupled carbon–nitrogen–sulfur metabolism. These results highlight that deterministic environmental filtering and metabolic complementarity jointly shape microbial P cycling across sediment depth gradients.
Overall, our findings reveal a depth-dependent reorganization of microbial phosphorus cycling strategies in mangrove sediments, emphasizing functional redundancy and metabolic cooperation as key mechanisms sustaining ecosystem processes under extreme nutrient limitation.
 

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