Deciphering the roles of abundant and rare microbial taxa in the natural restoration of organically contaminated urban river sediments.

Understanding the distinct roles of rare (RT) and abundant taxa (AT) during the natural restoration of organic contaminated urban river sediments is crucial for optimizing bioremediation. This study investigated their distribution, assembly mechanisms, co-occurrence patterns, and functional traits across sediment pollution gradients. Results revealed that AT dominated in sequence abundance but comprised fewer OTUs, while RT exhibited higher α-diversity and broader niche width, underpinning community stability under pollution stress. Stochastic processes dominated community assembly, with dispersal limitation primarily shaping AT and ecological drift influencing RT. Functionally, AT drove pollutant transformation and energy metabolism, whereas RT displayed elevated metabolic activity supporting microbial growth. Critically, RT demonstrated superior xenobiotic biodegradation in severely polluted sediments, highlighting their specialized role in extreme conditions. Co-occurrence network emphasized RT's importance in maintaining complex microbial interactions, though network stability decreased with pollution. These findings demonstrate that AT and RT synergistically drive organic matter degradation, with RT uniquely contributing to pollutant breakdown and ecosystem stability under high pollution stress. This study provides insights into leveraging both taxa for optimized bioremediation strategies in contaminated sediments.