Arbuscular mycorrhizal fungi reshape the resource strategies of competing plant species and drive cascading modulation through soil legacies in a shrub-dominated community

Arbuscular mycorrhizal fungi (AMF) play a pivotal role in plant resource acquisition and plant–plant interactions, thereby strongly influencing species coexistence and community diversity. However, it remains unclear how AMF modulate the resource-use strategies of interacting plants—particularly between shrubs and understory herbaceous species—and whether these effects persist through soil legacies. We conducted a plant–soil feedback experiment using two dominant species from the Mu Us Desert: the shrub Artemisia ordosica and the perennial grass Leymus secalinus. We quantified plant traits associated with resource-use strategies, soil nutrient availability, and microbial community composition under AMF inoculation and interspecific competition. Our results indicate that AMF enhanced the divergence in resource-use strategies between A. ordosica and L. secalinus under interspecific competition. In the presence of competitors, AMF shifted A. ordosica towards a more conservative strategy (increased leaf dry matter content, reduced specific leaf area) whereas L. secalinus shifted towards a more acquisitive strategy (decreased root: shoot ratio and root tissue density). In mixed-plantation soil legacies, AMF promoted the accumulation of soil nutrients and increased the abundance of putative pathogenic specialists associated with L. secalinus, while reducing putative saprotrophic specialists associated with A. ordosica. Furthermore, these AMF-mediated soil legacies generated contrasting performance outcomes in subsequent seedlings exposed to competition. These findings highlight the critical role of AMF in shaping divergent resource-use strategies among interacting plant species. This study advances our understanding of the mechanisms underlying plant–plant interactions and provides practical insights for optimizing shrub–grass configurations in ecological restoration.