Unraveling Microbial Drivers of Lacustrine N2O 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 N₂O 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 N₂O emissions. We demonstrate that, compared to warming or eutrophication alone, their synergistic interaction amplified N₂O flux by 100-fold and 3.5-fold, respectively. Nutrient loading exerts a dominant control over the regulation of N₂O dynamics, surpassing that of warming. Mechanistically, eutrophication elevates substrate availability, while warming enhances microbial utilization thresholds, synergistically escalating N₂O emissions. Microbial analyses reveal that nutrient enrichment increases (nirK + nirS)/nosZ and amoA abundance, whereas warming stimulates microbial enzyme activity. These dual stressors collaboratively reshape the microbial community structure, accelerating N₂O metabolic rates. In addition, thermal stimulation enhances the gas diffusion coefficient and accelerates the release of N₂O from the aqueous phase. Warming could cause the N₂O 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 N₂O emissions in warming ecosystems. Warming shifts lake N₂O emissions from nonlinear to linear patterns with increased nutrient levels via microbial dynamics, informing nutrient management for climate-resilient waters.