Aims Plant roots play a critical role in the uptake of nutrients, and nitrogen (N) absorption is considered as the first step and a pivotal process in N metabolism of plants. Our objective was to better understand the absorption of two major inorganic N forms (NH_4~+ and NO_3~-) in subalpine coniferous forests under global warming. Methods Experimental warming using infrared heater was applied to two dominant species in subalpine coniferous forests of Sichuan, China, Picea asperata and Abies fargesii var. faxoniana. The non-invasive micromeasurement technology was used to investigate the effects of warming on the uptake rates of NH_4~+ and NO_3~- and the potential interactions between these two ions. Important findings Results showed that the maximal net root uptake of NH_4~+ and NO_3~- occurred at a distance of 17-18 mm and 17 mm from root tips, respectively for P. asperata. and at a distance of 11 mm and 11.5 mm from root tips respectively for A. fargesii var. faxoniana. Experimental warming elevated the uptake rates of NH_4~+ and NO_3~- in both species, but the interactions between NH_4~+ and NO_3~- differed between the two species. While NO_3~- uptake was inhibited in the presence of NH_4~+ for both P. asperata and A. fargesii var. faxoniana, net NH_4~+ uptake was promoted by NO_3~- supply only in P. asperata roots under experimental warming.