Variability of microbial network complexity and stability along the size-fraction particles in the global ocean

Marine sinking particles serve as hotspots for microbial colonization and activity, with diverse microbes co-consuming particulate organic matter (POM) to recover essential nutrients. However, the interaction patterns between such diverse and complex microbial communities and its possible impact on the marine biological carbon pump (BCP) remains unclear. Here we analyze snapshots of microbial community composition on marine particles with different particle sizes collected during the Malaspina 2010 Expedition. We found that large sinking particle-attached microbial communities showed lower networks complexity and robustness, but stronger compositional stability. These communities were significantly enriched in organic carbon degradation functional genes, indicating its key role in the initial phases of carbon flux attenuation. These patterns are likely driven by strong homogeneous environmental selection and weak dispersal limitation, which lead to niche overlap, intensified negative interactions, and competitive exclusion among particle-attached microbes. We propose the hypothesis of “large particle eutrophication”, which indicates that the enrichment of bioavailable organic matter in large sinking particles promotes competitive microbial interactions, which allow only microorganisms with specific metabolic functions to colonize, leading to stronger compositional stability. Our results highlight the key ecological role of microbial community structure in regulating the carbon sink process, providing new theoretical support and ecological perspectives for understanding the marine carbon cycle.