Plastispheres as unique niches for promoting turnover of dissolved organic matter in aquatic environments

Plastic debris has been found to be ubiquitous in aquatic ecosystems, providing a novel substrate for biofilm formation called the plastisphere. Existing surveys mainly focus on the fact that this novel niche serves as a reservoir for environmental contaminants, whereas the potential role of the plastisphere in affecting biogeochemical cycles of aquatic dissolved organic matter (DOM), one of the largest pools of active carbon, remain largely unknown. Herein, we conducted in-situ field incubation and lab-scale microcosm experiments using river water as background, investigating the variation and underlying mechanisms of riverine DOM composition under plastisphere incubation at molecular level. Microcosm experiments showed that DOM content in water after plastisphere incubation significantly increased compared with that in the control group. Spectroscopy and ultrahigh-resolution mass spectrum further revealed that plastisphere distinctly accelerated the DOM transformation from labile-active components to recalcitrant-inactive molecules compared with natural biofilm, potentially contributing to riverine refractory DOM pool. Furthermore, the shifted microbial communityies (e.g., Proteobacteria and Acidobacteria) and functional gene abundance (e.g., carbon degradation/fixation and organic nitrogen/phosphorus mineralization) related with DOM transformation regulated by plastisphere were identified as main inherent mechanisms. Therefore, the prevalent plastisphere may alter the aquatic microbial functions, and consequently expedite the turnover of organic carbon and reshape DOM chemodiversity. These findings pinpoint plastisphere as a potential source and distinctive shaper for aquatic DOM, providing new insight into roles of this unique biotope in elemental biogeochemical cycling.