Colonization time of plastisphere drives the dynamics of organic carbon stability and microbial communities in seagrass bed sediments

Microplastic (MP) pollution in seagrass bed ecosystems has emerged as a significant global concern. However, the effects of plastisphere formation on organic carbon pools and microbial communities in these ecosystems remain unknown. We conducted a 56-day microcosm incubation experiment to study the dynamic changes in physicochemical characteristics, organic carbon fractions and stability, and bacterial community structure in seagrass bed sediments during the plastisphere formation process for polystyrene (PS) and polylactic acid (PLA). The results revealed significant weathering and biofilm formation on both PS and PLA. MPs altered the microbial community structure in seagrass bed sediments, leading to species turnover. Colonization time emerged as the key factor driving microbial community assembly, with ecological processes shifting from dispersal limitation to ecological drift in the plastisphere, while sediments maintained dispersal limitation as the dominant process. The formation of the plastisphere significantly influenced seagrass bed sediment microbial carbon (MBC) and organic carbon pool stability. MPs weathering negatively correlated with sediment properties but positively correlated with microbial communities, jointly modulating carbon pool stability. This study provided a new insight into the potential risks posed by MPs to carbon cycling and the ecological functioning of seagrass bed ecosystems.