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Arbuscular mycorrhizal fungi (AMF) play a vital role in mediating rhizosphere interactions and plant growth, especially in resource-constrained soils. However, few studies have documented the effects of AMF on plant–plant interaction patterns and resource use efficiency along stress gradients. In this study, a growth environment-controlled experiment was carried out to evaluate the effects of AMF inoculation on maize-grass pea intercropping along three phosphorus (P) and two water gradients. The data indicated that soil water and P availability determined the plant interspecific interaction pattern, and that interaction was strongly mediated by AMF inoculation. Grass pea and maize were mutually facilitated under low P and water conditions and transitioned to a new pattern, i.e., that maize was facilitated but grass pea was neutral role or facilitator with increasing resource availability. The facilitative effect was particularly significant under P- and water-deficient conditions. Moreover, the transition of the plant–plant interaction pattern was mechanically driven by improving rhizospheric phosphatase activities by 5.08–20.02 %, rhizospheric acidification and enhanced microbial activities under resource deficit conditions. Critically, AMF inoculation was observed to significantly improve rhizospheric soil P availability and microbial biomass (p < 0.05); however, it enhanced the complementary utilization of P and water and weakened interspecific competition under high-resource conditions. Therefore, AMF inoculation positively transformed the plant–plant interaction pattern along resource gradients for higher P, nitrogen and water use efficiency. This study validates the context-dependent interspecific interaction and the role of AMF in optimizing resource use in a nutrient-impoverished intercropping system. Illustrating the effect of AMF inoculation on plant growth and plant–plant interaction in maize-grass pea intercropping system. [Display omitted] • Plant diversity increased rhizosphere microbial activity and phosphatase secretion. • AMF inoculation enhanced facilitation intensity with increasing stress conditions. • AMF lowered interspecific competition intensity for higher resource use efficiency. [ABSTRACT FROM AUTHOR]