Nitrogen (N) and phosphorus (P) stoichiometry in plant leaves plays an important role in linking plant physiological processes with community assemblage and species distribution. Studies have revealed that temperature is a major driver of leaf stoichiometry, however, whether current global warming will alter leaf N and P stoichiometry on a local scale remain poorly understood. Taking advantage of an unique data set on leaf element concentrations of 122 plant species in the Xilingol Grassland National Reserve (established in 1979), we addressed this issue by resampling plant leaves of the same 121 species in 2018, and compared the leaf N, P, and N:P ratio between the 2 years. We found that leaf N, P, and N:P ratio of the 121 species all exhibited large variation, with a magnitude of 4.5-fold for N, 5.8-fold for P, and 6.3-fold for N:P ratio, respectively. However, the mean leaf N, P, and N:P ratio of the 121 species, as well as for each family, each life form and each habitat type, did not significantly change over 40 years (1979 vs. 2018), though a 2°C increase in annual mean temperature occurred. We identified that taxonomic difference was the primary driver for variations in leaf N, P, and N:P ratio in this grassland reserve, which is different from those on the regional and global scales. These results suggest that controls over leaf stoichiometry are likely scale-dependent. Thus, using leaf stoichiometry to explain community assemblage and species distribution should take into account the scale-dependent drivers.