Effect of resource supply on interactions between foliar endophytic and root mycorrhizal fungi in perennial ryegrass.

Both foliar endophytes and root arbuscular mycorrhizal fungi can infect perennial ryegrass and improve its performance, mainly by improving herbivore resistance and phosphorus (P) uptake, respectively. Here, we report a study of how the endophytic fungus (Neotyphodium lolii) and two mycorrhizal fungi (Glomus spp.) are affected by P supply and perennial ryegrass (Lolium perenne) cultivars differing in water soluble carbohydrate content. Endophyte and alkaloid concentrations were reduced at high P supply and in the high sugar grass (HSG) ‘AberDart’, and these effects were modulated by the presence of mycorrhizal fungi. High P supply resulted also in a strong reduction of mycorrhizal colonisation, while the effect of the high sugar grass was subtle and modulated by endophyte infection. Our results show that the simultaneous association of perennial ryegrass with both endophytic and mycorrhizal endosymbionts can negatively affect each endosymbiont, but this depends on other factors such as resource supply and genetic background of the partners.