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Aims Nitrogen (N) deposition is an important component of global change and threatens terrestrial biodiversity. The response of plant–soil microbe relationships to N deposition has recently attracted considerable attention. Soil microorganisms have been proven to provide nutrients for specific plant growth, especially in nutrient-poor desert steppe ecosystems. However, the effects of N deposition on plant soil microbial community interactions in such ecosystems remain poorly understood. Methods To investigate these effects, a six-year N-addition field experiment was conducted in a Stipa breviflora desert steppe in Inner Mongolia, Northwest China. Four N treatment levels (N0, N1, N2, and N3, corresponding to 0, 30, 50, and 100 kg N ha-1 yr-1, respectively) were applied to simulate atmospheric N deposition. Results The results showed that (1) after six years of simulated N deposition, plant aboveground biomass did not increase, but plant community structure changed; (2) In desert steppes, N addition increased the biomass of Neopallasia pectinata, and the correlations between N. pectinata and microorganisms also increased. However, the biomass of the perennial grass S. breviflora decreased, and the correlation with soil microorganisms was weaker for S. breviflora than for N. pectinata; (3) N deposition indirectly affects plant biomass mainly by inhibiting (or promoting) the number of microorganisms negatively correlated with plant growth. Conclusions These results suggest that N deposition alters plant community structures and biomass by affecting plant–soil microbe relationships in desert steppes. These findings help clarify atmospheric N deposition effects on the ecological health and function of desert steppes.

Aims Nitrogen (N) deposition is an important component of global change and threatens terrestrial biodiversity. In past decades, the response of the relationship between plants and soil microbes to N deposition has attracted considerable attention. Keystone microbial taxa have been proven to provide nutrients for specific plant growth, especially in nutrient-poor desert steppe ecosystems. However, the effects of N deposition on plant and soil microbial community interactions in desert steppe regions remain poorly understood. Methods To investigate these effects, a six-year N-addition field experiment was conducted in a Stipa breviflora desert steppe in Inner Mongolia, Northwest China. Four N treatment levels (N0, N1, N2, and N3, corresponding to 0, 30, 50, and 100 kg N ha-1 yr-1, respectively) were applied to simulate atmospheric N deposition. Results The results showed that (1) after the six-year N deposition simulation, the plant aboveground biomass did not increase, but the plant community structure changed; (2) in desert steppes, the relationship between microorganism communities and Neopallasia pectinata was strengthened by N addition, while that between microorganism communities and S. breviflora was simplified; and (3) N deposition indirectly affected the plant biomass in desert grasslands, mainly along key-stone microbial taxa pathways. Conclusions Together, these results suggest that N deposition can alter plant community structures by affecting the relationships between plants and soil microorganisms in desert steppes. These findings contribute to a comprehensive understanding of the effects of atmospheric N deposition on the ecological health and function of desert steppes.