Arbuscular mycorrhizal fungi regulate the diversity–invasion resistance relationship by influencing the role of complementarity and selection effects

Arbuscular mycorrhizal fungi (AMF) play a crucial role in influencing plant community dynamics, yet their impact on the relationship between plant diversity and resistance, especially resistance to plant invasion, remains largely unclear. We conducted an experiment using plant communities with varying species richness (one, three and six species) and subjected them to invasion by Solidago canadensis and AMF inoculation. We measured community resistance by comparing the biomass of invaded communities to uninvaded communities and investigated the effect of AMF inoculation on the diversity-resistance relationship. Our results indicate that communities with higher plant species richness displayed greater resistance to invasion, and this effect was stronger in the presence of AMF than in its absence. AMF inoculation weakened the positive complementarity effect-resistance relationship (i.e. a decreasing species asynchrony) due to AMF-induced alterations in community composition, but shifted the negative selection effect-resistance relationship to neutral (i.e. a negative-to-neutral sampling effect) due to the enhanced role of the dominant species Mosla scabra. Furthermore, the AMF-induced changes in plant species resistance were positively correlated with their relative growth rate and specific root surface area. These findings suggest that AMF inoculation alters the mechanisms underlying diversity-resistance relationships, with implications for how plant communities respond to disturbances such as invasion.