AM fungus improves the competitiveness of a native plant against an invasive plant under moderate soil P supply

Background Alien invasive plants have severely threatened the invaded habitats' structural stability and species diversity. The positive impacts of arbuscular mycorrhizal (AM) fungi on the successful invasion of some alien plants have been well documented, whereas soil phosphorus (P) frequently affects AM fungi benefits. Nevertheless, how soil P availability affects AM fungal function and then shifts the competitive direction of congeneric invasive and native plants remains unclear. Methods A pot experiment was conducted. Specifically, the AM fungus treatments were inoculation or non-inoculation with Claroideoglomus etunicatum ; the P addition treatments included three different rates of P supply; the competition styles contained intraspecific competition of invasive Eupatorium adenophorum and congeneric native Eupatorium lindleyanum respectively and interspecific competition when the two plant species were grown together. Plant biomass and nutrients were analyzed. Results The results showed that AM fungus promoted the growth and nutrients of E. adenophorum and E. lindleyanum . P addition decreased the mycorrhizal response of the two species under intraspecific competition but increased the mycorrhizal responses of E. lindleyanum under interspecific competition. The relative yield and competitive aggressivity showed that E. lindleyanum had significantly greater competitiveness than E. adenophorum . AM fungus further improved the competitive aggressivity of E. lindleyanum under moderate P addition, while it did not influence the competitive aggressivity in biomass of the two species under low and high P conditions. Conclusion AM fungus enhances the competitiveness of a native plant over an invasive plant with a moderate soil P supply.