Nitrogen （N） and phosphorus （P） additions are vital management methods to alleviate plant nutrient limitation and improve grassland productivity. Soil nutrient enrichment may potentially alter the symbiotic relationships between plants and arbuscular mycorrhizal fungi （AMF）. This study conducted a three-factor experiment to study the independent and interactive effects of N and P additions and AMF on the biomass and C∶N∶P of Agropyron mongolicum and Astragalus melilotoides in the desert steppe in Ningxia. We used a kind of fungicide（benomyl）to regulate native AMF activities. Our results showed that N and P additions significantly increased the aboveground biomass of A. mongolicum and A. melilotoides， but AMF did not alter them. AMF significantly reduced the aboveground biomass of A. mongolicum under P alone addition and both N and P addition treatments. AMF increased the C∶N of A. mongolicum plants and the C∶P of A. melilotoides. P addition significantly reduced the C∶P and N∶P of two plants， and alleviated the P limitation of A. mongolicum. In summary， compared with AMF， N and P addition was more beneficial to dominant plants biomass in the desert steppe in Ningxia， and could alleviate the nutrient limitation of A. mongolicum and A. melilotoides.

Agropyron mongolicum  /  Astragalus melilotoides  /  Ecological stoichiometric ratio  /  Nutrient content  /  Phosphorus limitation