Simulated freeze–thaw cycles restructure plastisphere microbiomes and functional gene co-occurrence networks in alpine lake sediment microcosms

Microplastics (MPs) are increasingly recognized as dynamic ecological interfaces rather than inert contaminants, yet their role in shaping microbial functional interactions under climate-driven disturbances remains poorly understood. In particular, how climate driven freeze-thaw cycles (FTCs) influence the dynamics of mobile genetic elements (MGEs) within the plastisphere remains unclear. Here, we used controlled microcosms containing sediments from Tibetan Plateau lakes and polyethylene/polyethylene terephthalate particles to examine how simulated extreme FTCs were associated with changes in plastisphere microbial communities and functional gene co-occurrence patterns. FTCs reshaped plastisphere microbial communities, but their assembly trajectories differed between habitats. In the plastisphere, deterministic selection was pronounced at early FTC stages, whereas it did not further intensify with increasing FTC frequency. In contrast, sediment communities exhibited a progressive shift toward deterministic assembly with increasing FTCs. Concomitantly, MGEs were relatively enriched in the plastisphere and co-occurrence with genes involved in carbon metabolism, antibiotic resistance genes (ARGs), and virulence factors (VFs), forming interconnected functional networks. Notably, FTCs were associated with the enrichment of specific carbon metabolizing taxa (e.g., Comamonas and Brevundimonas) within the plastisphere that also carried relatively high abundances of MGEs, ARGs, and VFs. These patterns suggest that MPs may provide ecological niches linking carbon utilization and gene exchange potential. Collectively, this work highlights the interactive influence of climate-related disturbance and emerging pollutants on plastisphere microbial ecology, and provides a mechanistic basis for future assessment of ecological implications in fragile alpine ecosystems.