Plant nitrogen (N) uptake is a critical ecosystem function, especially when terrestrial ecosystems are threatened worldwide by increasing anthropogenic N deposition. However, the mechanisms by which biotic factors mediate the effects of increases in N addition on community N uptake remain unknown. Here, we determine how inter- and intraspecific differences contribute to this response by decomposing N uptake in a specific community in a 7-year NH₄NO₃ addition experiment in a Tibetan alpine meadow using variance partitioning approach. We measured both plant N uptake from ammonium and nitrate of 25 common species in control plots and community-level uptake along a N addition gradient, using short-term in situ ¹⁵N labeling. Plant community composition, soil properties (soil ammonium and nitrate, pH, Al³⁺ and base cations), soil microbial biomass carbon and nitrogen were measured and recorded. We found that N addition increased community-level N uptake by significantly increasing individual species’ variability of N uptake (that is, positive intraspecific variability), although with limited effect of community composition shift. The significantly positive intraspecific variability from ammonium and nitrate along the N addition gradient was caused by increased soil available N and soil acidification with N addition. The limited effect of community composition shift means that N addition increased community-level N uptake with only limited species filtering. Our results provide a novel insight into the mechanism of how N addition affects community-level N uptake, by linking physiological, community and ecosystem function, and highlight the important role that intraspecific variability of N uptake plays.