Human activities have significantly increased global atmospheric nitrogen (N) deposition, altering its compound composition. However, our understanding of how N compound composition affects plant growth remains limited. We conducted a greenhouse pot experiment with 16 treatments—control and N addition at 10 g N·m-2·a-1 with four predominant compounds (ammonium, nitrate, urea, and glycine) found in atmospheric N deposition and their mixtures—to investigate their impact on the growth of Chenopodium glaucum L. The results showed that regardless of the N compound composition added, N addition enhanced plant above-ground (AGB) and below-ground (BGB) biomass, as well as total biomass (TB). Notably, only the combined organic-N (urea + glycine) treatment significantly boosted AGB and TB, whereas the blend of inorganic-N (ammonium + nitrate) along with glycine addition notably stimulated BGB. Structural equation modeling revealed that, irrespective of the N compound composition added, N addition stimulated plant growth by directly elevating soil ammonium levels and concurrently augmenting the photosynthetic potential of leaves and stem girth, although elevated soil ammonium levels due to N addition diminished BGB. These findings suggest that the composition of N compounds has significantly effects on plant growth. Therefore, similar treatments should be conducted at the community and ecosystem levels to more accurately assess the impacts of atmospheric N deposition on ecosystem structure and functioning.