Regulatory mechanisms of total phosphorus on N₂O concentrations: A case study of Dongting lake

Lakes serve as critical regulators of biogeochemical processes, acting as hotspots for nitrous oxide (N₂O) emissions while simultaneously retaining substantial phosphorus loads. However, the role of total phosphorus (TP) in shaping N₂O dynamics remains poorly understood. Here, we investigated TP-mediated changes in N₂O concentrations in Dongting Lake, China, using a classification framework based on national water quality standards, validated with the GRiMe dataset and machine learning approaches. We performed a comprehensive analysis of environmental parameters, microbial community composition, and nitrogen-cycling functional genes, revealing that TP strongly influences N₂O dynamics through complex microbial pathways. Under low TP, N₂O concentrations were significantly higher. As TP increased, microbial community structure shifted, nitrogen-cycling gene abundances (e.g., amoA of AOA, nirK, and nosZ) rose significantly, and denitrification completeness improved, collectively enhancing N₂O reduction capacity. Notably, bacterial communities exhibited stronger stochastic assembly under low TP, whereas archaeal and fungal communities were dominated by deterministic processes, highlighting domain-specific responses to TP fluctuations. Structural equation modeling indicated that TP regulates N₂O primarily by altering gene abundance and microbial diversity, although these effects are modulated by carbon and nitrogen availability. These microbial and functional changes contribute to pronounced spatial heterogeneity in N₂O levels, posing challenges for prediction and management. Overall, this study provides new mechanistic insights into how TP shapes N₂O concentrations in freshwater ecosystems and underscores the critical importance of phosphorus management in strategies aimed at mitigating eutrophication and reducing greenhouse gas emissions in a changing climate.