Allelopathy and arbuscular mycorrhizal fungi interactions shape plant invasion outcomes

The novel weapon hypothesis suggests that allelopathy is an important mechanism for exotic plants to successfully invade native plant communities. Allelochemicals from exotic plants affect both native plants and arbuscular mycorrhizal fungi (AMF) in soil. To explore these effects, we conducted pot experiments using a native plant community comprising of Chenopodium album L., Vitex negundo L., Rhus chinensis Mill., and Acer truncatum Bunge. We incorporated AMF strains (Funneliformis mosseae, Glomus versiforme, and Rhizophagus intraradices in a 1:1:1 volume ratio) into a soil mixture comprising equal volumes of autoclaved field soil and grass ash at five concentrations (0 g L–1, CK; 10 g L–1, LRE; 20 g L–1, NRE; 30 g L–1, MRE; and 40 g L–1, HRE) to investigate the allelopathy of Rhus typhina L. root and its interactions with AMF on the native plant community. Our results indicated that low concentrations of allelochemicals promoted the relative growth rate and leaf nitrogen content in the native plant community, which was attributed to the increased environmental stress that improved the degree of leaf photosynthetic capacity and organic synthesis rate in the native communities. Moreover, allelochemicals with toxicity decreased the colonization rates of AMF. Meanwhile, the presence of allelopathic effects induced a decrease in leaf nitrogen, and allelopathy altered the effects of AMF on the native community. Specifically, the high concentration of allelochemicals altered the positive effect of AMF on the total aboveground biomass of the native plant community to a negative effect, likely by decreasing colonization rates or affecting soil physicochemical properties and the composition of the mycorrhizal communities. Consequently, it is necessary to consider the effects of AMF when testing the roles of allelopathy or the novel weapons hypothesis in biological invasions. Graphical abstract