Microplastics (MPs) and nanoplastics (NPs) are emerging contaminants in deep-sea ecosystems, yet their specific impacts on the internal heterogeneity of cold seep microbiomes remain poorly understood. Here, microcosm experiments with cold seep sediments exposed to polyethylene particles were conducted to investigate the response patterns of abundant and rare taxa to MP/NP-induced disturbances. The results indicated that MPs/NPs exposure reshaped bacterial community structure, with significant enrichment of Epsilonbacteraeota, a phylum associated with chemoautotrophic metabolism. In contrast, archaeal alpha diversity showed no significant response to MPs/NPs exposure. Abundant and rare taxa exhibited contrasting responses in community composition, assembly patterns, and network associations. Despite stochastic processes largely governing overall community assembly, the assembly mechanism of rare bacteria shifted toward heterogeneous selection under NPs exposure, which contrasted sharply with the homogeneous selection observed in the rare archaea. Furthermore, network analysis revealed that rare taxa constituted the majority of nodes in both co-occurrence networks. Functional predictions suggested contrasting responses, with lower relative abundances of taxa assigned to sulfate respiration in abundant bacteria under most treatments and higher relative abundances of taxa assigned to sulfur oxidation and nitrogen cycling in rare taxa under some treatments. Overall, this study highlights the contrasting responses of abundant and rare taxa to MPs/NPs exposure and provides insights for assessing the ecological risks of plastic pollution in deep-sea environments.
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