Intertidal sediments are important sites for carbon storage at the land–ocean interface. The burial, transformation, and remineralization of organic carbon in these sediments are jointly regulated by microbial communities and their associated viruses. However, how microbe–virus interactions affect sediment carbon cycling and their potential links to biological carbon pump (BCP) processes remains poorly understood. In this study, we investigated 55 sediment samples collected from 14 representative intertidal sites along the Bohai Sea, Yellow Sea, and East China Sea coasts of China. Using metagenomic sequencing, viral identification, host prediction, and functional annotation, we examined the spatial distribution, metabolic potential, and ecological relationships of microbial and viral communities.
Geographic location and sediment physicochemical properties significantly influenced the composition and functional distribution of microbial and viral communities. Metabolic stratification was observed within the upper 10 cm of sediment profiles. Surface layers were enriched in functions related to organic matter degradation and primary production, whereas deeper layers were characterized by anaerobic metabolism, fermentation, and elemental cycling, showing clear patterns of niche succession along the depth gradient. Virus–host association analyses further indicated that viruses frequently infect key microbial groups involved in carbon cycling. Through host lysis and auxiliary metabolic genes, viruses may influence microbial metabolism and carbon transformation processes.
Our findings suggest that virus–host interactions may be involved in carbon transformation processes linked to both microbial carbon pump (MCP) and BCP pathways, with potential effects on carbon storage efficiency and carbon cycling stability in intertidal sediments. This study highlights the joint roles of microbial and viral communities in shaping carbon cycling across both regional and vertical gradients in Chinese coastal intertidal sediments, improving our understanding of carbon sink functions in coastal ecosystems and their responses to environmental change.
 

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