Warming-enhanced soil methane uptake is suppressed by nitrogen deposition in a saline-alkali grassland

Saline-alkali grassland ecosystems are essential methane (CH₄) sinks, playing a significant role in global CH₄ budgets. However, our understanding of the CH₄ uptake potential in saline-alkali grasslands and its response to climate warming and nitrogen deposition remains unclear. A three-year (2023-2025) in-situ experiment with climate warming and nitrogen deposition treatments was carried out in the saline-alkali grasslands in the Hexi Corridor, Northwest China, aiming to uncover the temporal dynamics of CH₄ fluxes and their potential drivers. The results demonstrated that warming significantly promoted soil CH₄ uptake by 98.70%, driven by shifts in the structural and abundance of soil fungi and bacteria. Although nitrogen addition alone did not alter the CH₄ uptake rate, it significantly attenuated the positive effect of warming on CH₄ uptake in saline-alkali grasslands. This was driven by the change of soil microbial abundance and community structure, nutrient availability, and enzyme activity. Furthermore, we found that soil temperature, water content, dissolved organic carbon, and ammonium nitrogen were key abiotic factors influencing CH₄ uptake, while soil microbial biomass carbon, cellulase activity, and fungal and bacterial community composition emerged as primary biotic factors on CH₄ uptake. These results indicate that nitrogen deposition can significantly reduce CH₄ uptake fluxes in northwestern saline-alkali grasslands under future global warming. This study provides theoretical support for understanding CH₄ budget changes and their potential driving mechanisms under climate change.