To explore the effects of nitrogen （N） deposition on interspecific associations and niches of grassland plants， this study was conducted in the Horqin typical steppe. Nine treatments were set up， including the addition of inorganic N （I） and organic N （O） at three rates （0， 4， and 8 g·m^-2·a^-1） and their combinations（I₀O₀， I₄O₀， I₈O₀， I₀O₄， I₀O₈， I₄O₄， I₈O₄， I₄O₈， and I₈O₈）. The results showed that the plant community exhibited a random distribution under the treatments without inorganic N addition， a positive association under the I₄O₀ treatment and a negative association under the I₈O₀ treatment. Niche responses were species-specific： the niche breadth of Bassia prostrata in the I₈O₄ treatment was 58.3% higher than that in the I₄O₈ treatment （P<0.05）； Agropyron cristatum maintained a relatively high and stable niche breadth （0.32~0.36） across all treatments， and the proportion of high niche overlap of this species reached 87% under the I₈O₈ treatment. The ecological response rate （R=2.65-2.97） and niche overlap index （ΔO_ik=0.120~0.138） of A. cristatum were relatively stable； the R value of Artemisia scoparia surged to 140.50 under the I₈O₀ treatment； the R value of Lespedeza davurica remained negative （-1.62 to -0.66） with ΔO_ik<0. In conclusion， N addition enhances the negative interspecific associations of the community and niche differentiation， leading to variations in resource use efficiency among species.

Nitrogen addition  /  Interspecific association  /  Niche  /  Temperate steppe