Core microbiota in multitrophic communities regulate nitrogen metabolism in aquatic ecosystems: Evidence from Changtan reservoir

Exploring the effects of multitrophic microbiota on nitrogen transformation processes and evaluating the contributions of core microbiota in multitrophic groups are critical for nitrogen management in reservoirs. However, current studies have largely focused on bacterial communities, neglecting the profound roles of multitrophic interactions in biogeochemical processes. Here, we employed a multi-omics approach in Changtan Reservoir to investigate multitrophic community dynamics, their effects on nitrogen transformations, and the contributions of core taxa. Our results revealed that multitrophic community composition regulated nitrogen transformation processes primarily via trophic cascades driven by top-down predation, bottom-up resource allocation, and species interaction, with core taxa acting as dominant contributors. Analysis of community drivers indicated that multitrophic α- and β-diversity was mainly affected by biotic factors, except for bacterial and fungal richness. Co-occurrence networks demonstrated that multitrophic taxa were directly linked to nitrogen-metabolizing genes, with competitive interactions outweighing positive ones, particularly in denitrification, N₂ fixation, and nitrification processes. Temporal dynamics showed that competition with algae suppressed nitrification in spring, while competition with Cyanobacteria promoted N₂ fixation in summer. Invertebrate bioturbation was identified as a key factor leading to declined denitrification in autumn. Furthermore, core taxa were essential for maintaining network stability and modulating nitrogen-metabolizing gene abundance by community assembly and multitrophic β-diversity. These findings highlight the significance of incorporating multitrophic interactions and core taxa dynamics into aquatic nitrogen management strategies and policy formulation, proposing the enhancement of multitrophic diversity and cross-trophic synergy as viable approaches to optimize nitrogen cycling in reservoir ecosystems.