Comparison of the Environmental Adaptation Strategies of Abundant and Rare Taxa in the Sediments of the Northwestern South China Sea

Understanding microbial community assembly mechanisms is central to understanding ecosystem stability and environmental adaptation strategies. However, depth-dependent patterns and their driving factors in the community assembly of abundant and rare taxa in subtropical bay sediments remain poorly understood. In this study, 16S rRNA sequencing was employed to analyze sediment microbial communities across depth gradients at 10 sites in the northwestern South China Sea. The results revealed that rare bacterial communities exhibited high sensitivity to depth variation. Functional prediction revealed that rare taxa drive ecosystem multifunctionality via a broader range of diverse C/N/S transformations (including unique pathways such as lactate-to-acetate conversion and sulfur oxidation), whereas abundant taxa specialize in stable core energy metabolism (such as glycolysis and the tricarboxylic acid cycle (rTCA) cycle) and exhibit robust environmental adaptability through metabolic flexibility and strong network connectivity. Community assembly mechanisms indicated that deterministic processes dominated the assembly of rare taxa with 47%–67% contribution rates. In contrast, the abundant taxa were primarily regulated by dispersal limitation (average proportion: 57%) and drift (average proportion: 43%). Co-occurrence networks revealed strong connections between abundant and rare taxa with abundant taxa playing a critical role in maintaining ecological network stability. In conclusion, this study provides new insights into the environmental adaptation strategies of abundant and rare bacterial communities in subtropical marine sediments and establishes a theoretical framework for understanding the depth-dependent microbial dynamics in coastal ecosystems.