Plant interactions may directly affect plant growth, root plasticity and nutrient uptake, while arbuscular mycorrhizal (AM) symbioses can redistribute resources among plants at both individual and community levels, and consequently mediate plant interactions and influence plant community structure. In the present study, a pot experiment was carried out to investigate the influences of indigenous mycorrhizal fungi and neighboring plants, Medicago sativa and Lepidium spetalum, on the growth and phosphorus nutrition of Leymus chinensis, a dominant grass species on the meadow steppe in North China. At experimental harvest, plant growth, root morphology and phosphorus uptake of both plant species were recorded. The results indicated that the indigenous mycorrhizal fungi formed symbiosis with L. chinensis and M. sativa, but not with non-host plant, L. spetalum, while in the non-mycorrhizal treatment where mycorrhizal fungi were eliminated by radiation sterilization, the mycorrhizal colonization rates were generally lower than 2%. The indigenous mycorrhizal fungi significantly suppressed the growth of L. chinensis and L. spetalum, but promoted growth of M. sativa. Neighboring plant M. sativa promoted, but L. spetalum suppressed the growth of L. chinensis. Analysis of variance showed that mycorrhizal fungi and neighboring plants exhibited significant interactions on mycorrhizal colonization. The effects of mycorrhizal fungi on the root length and root surface area were similar with that on plant biomass, but plant combinations showed no significant effects. As for plant phosphorus concentration, both mycorrhizal fungi and plant combinations showed no significant effects. Compared to the neighboring plants, L. chinensis had higher relative root length and P uptake efficiency, which can well explain its negative responses to mycorrhizal fungi. The study demonstrated that mycorrhizal fungi and plant interactions are important factors influencing plant growth and root proliferation. Further studies are still necessary for a better understanding of the importance of mycorrhizal fungi in maintaining plant community stability and productivity, and also for sustainable management of the grasslands.