Warming Intensifies Nitrogen-Driven Destabilization of Alpine Soil-Dissolved Organic Matter

Soils in alpine grasslands of the Qinghai-Tibet Plateau store vast carbon stocks that influence global climate, yet it is unclear how warming and nitrogen enrichment interactively regulate dissolved organic matter (DOM), the most readily degradable carbon pool. Using a 12-year field experiment, we investigated how these pressures interactively regulate DOM and microbial characteristics. Nitrogen addition substantially increased dissolved organic carbon (DOC), whereas warming exerted comparatively moderate effects. Their impacts on DOC accumulation were largely additive rather than synergistic, suggesting that resource availability constrains carbon responses under multiple global change drivers. In contrast, warming significantly amplified nitrogen-induced shifts in DOM quality, decreasing aromaticity, and increasing biolability. These changes were mediated by the expansion of copiotrophic taxa and enrichment of resource-acquisitive functional traits alongside shifts in soil chemical conditions. In turn, alterations in DOM quantity and quality were associated with shifts in microbial community structure and metabolic strategies, particularly under increased inputs of microbially derived labile substrates. Together, our findings indicate that warming intensifies nitrogen-driven acceleration of carbon turnover in alpine grasslands, highlighting the importance of climate-nutrient interactions in predicting future carbon-climate feedbacks.