Unraveling Microbial Drivers of Lacustrine NO Emissions under Synergistic Warming and Eutrophication: Community Dynamics and Functional Gene Responses.

Climate warming and eutrophication reshape nitrogen cycling in lakes, yet their combined impacts on lacustrine NO source-sink dynamics and underlying microbial drivers remain poorly resolved. Here, a controlled microcosm experiment was constructed to explore the interaction and microbial mechanism of warming (+4 °C) and nutrient enrichment (low, middle, and high nutrient gradients) to NO emissions. We demonstrate that, compared to warming or eutrophication alone, their synergistic interaction amplified NO flux by 100-fold and 3.5-fold, respectively. Nutrient loading exerts a dominant control over the regulation of NO dynamics, surpassing that of warming. Mechanistically, eutrophication elevates substrate availability, while warming enhances microbial utilization thresholds, synergistically escalating NO emissions. Microbial analyses reveal that nutrient enrichment increases ( + )/ and abundance, whereas warming stimulates microbial enzyme activity. These dual stressors collaboratively reshape the microbial community structure, accelerating NO metabolic rates. In addition, thermal stimulation enhances the gas diffusion coefficient and accelerates the release of NO from the aqueous phase. Warming could cause the NO emissions shift from a unimodal nonlinear pattern to linearity with elevated eutrophic level. Our findings establish a mechanistic framework linking climate-nutrient interactions to microbial N-cycling, providing critical insights for predicting and mitigating lacustrine NO emissions in warming ecosystems. Warming shifts lake NO emissions from nonlinear to linear patterns with increased nutrient levels via microbial dynamics, informing nutrient management for climate-resilient waters.