Micro-ecosystem of plastisphere in high-altitude lake: Hotspots of anaerobic carbon cycle distinct from sediments

Microplastics (MPs) have an impact on microbial community assembly and biogeochemical cycles in aquatic ecosystem, but the intrinsic carbon cycle within plastisphere remains unknown. Here, we compared carbon cycling in plastisphere of three major MP polymers i.e., polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) versus sediments in a high altitude lake on the eastern Qinghai-Tibet Plateau. The plastisphere was identified as carbon cycling hotspots, exhibiting distinct microbial assembly and functional patterns from sediments. The PET plastisphere demonstrated the most active anaerobic carbon metabolic activities, with microbial communities dominated by methanogenesis and fermentation pathways and methanogenic gene abundance far exceeding that in the PP and PE plastisphere. Sediments contained functionally diverse communities dominated by methane-oxidizing archaea and carbon-fixing bacteria, facilitated by stable redox gradients that drive various carbon transformation pathways. Community assembly in the plastisphere was primarily driven by stochastic processes, whereas sediment communities were influenced by environmental filtering. Homogenizing selection was stronger in PET plastisphere, favoring the enrichment of specific functional taxa. The findings reveal that MPs influence microbial community structure and metabolic function and the plastisphere is an independent driver of carbon cycling. This study provides new evidence of plastisphere-driven carbon metabolism, highlighting its role as localized greenhouse gas generator, and its divergence from sediment-mediated carbon cycling in lake ecosystems.