Warming and Nitrogen Addition Induce Asynchronous Taxonomic and Functional Responses and Reorganize Microbial C, N, P Cycling Potential in an Alpine Wetland on the Qinghai–Tibet Plateau

Abstract

Climate warming and atmospheric nitrogen deposition are altering carbon (C), nitrogen (N), and phosphorus (P) cycling in alpine wetlands. However, how these drivers jointly reorganize microbial communities and their biogeochemical cycling potential remains poorly understood, particularly in cold, nutrient-limited alpine wetlands. We conducted a four-year field experiment combining open-top chamber warming and nitrogen addition. Soil physicochemical measurements were integrated with shotgun metagenomic sequencing to assess microbial community structure and the functional potential associated with C, N, and P cycling. The results showed that archaeal and bacterial community composition remained stable following warming and nitrogen addition, whereas fungal composition changed. Functional gene richness was positively correlated with archaeal and bacterial richness but was not correlated with fungal richness, indicating asynchronous responses between taxonomic–functional dimensions. Warming and nitrogen addition did not consistently increase the overall abundance of C, N, and P cycling functional genes. Instead, they induced pathway-specific responses: compensatory shifts among C fixation pathways, decreases in complex C degradation genes, increases in nitrification genes, and decreases in genes associated with P acquisition and homeostatic regulation. Soil moisture and enzyme activities were significantly correlated with C, N, and P cycling genes. These findings highlight domain-specific taxonomic responses and process-specific re-organization of microbial functional potential and emphasize the importance of hydro-thermal constraints when predicting alpine-wetland biogeochemical responses to future warming and increasing N inputs.