Dissolved Organic Carbon Shapes Sediment Bacterial Diversity in Continental Lakes

Biodiversity patterns such as the latitudinal diversity gradient (LDG) are central to ecology. Compared to macroorganisms, microbial diversity patterns and their underlying mechanisms, particularly in freshwater systems, are understudied despite their importance to ecosystem functioning. Here, we conducted a large-scale investigation of sediment bacterial communities in China's lakes across a latitudinal gradient from 18°N to 50°N and assessed their diversity patterns, life history strategies, and co-occurrence networks. Bacterial alpha diversity showed nonsignificant latitudinal pattern, but the community composition exhibited a significant distance-decay relationship. Climate factors, including mean annual temperature, were not correlated with alpha diversity, which is inconsistent with the "Red Queen" hypothesis. Instead, carbon resources indicated by the absorption coefficients at 254 nm and humification index of dissolved organic matter were positively associated with alpha diversity, supporting the "Resource Partitioning" hypothesis. The quality and quantity of dissolved organic matter also influenced life history traits (e.g., rrn copy number, oligotrophic-copiotrophic ratios) and co-occurrence network properties, with increasing refractory carbon decreasing the ratio of negative to positive network cohesion. Dissolved organic matter influenced bacterial diversity primarily through its indirect effects on life history strategies and potential biotic interactions revealed by structural equation modeling. Our findings highlight the dominant role of carbon resources over climate in structuring sediment bacterial diversity in freshwater ecosystems.