Arbuscular mycorrhizal fungi can shift plant-soil feedback of grass-endophyte symbiosis from negative to positive

Plants affect each other by modifying soils conditions in plant-soil feedbacks, where associated microbes have an integral role. Since epichloid endophytes and arbuscular mycorrhizal fungi (AMF) are highly widespread grass symbionts, here we explore the role of AMF and endophyte in plant-soil feedback within the same grass population. Through a manipulative experiment, we evaluated the performance of endophyte-free and endophyte-associated Lolium multiflorum plants grown in soils previously conditioned by endophyte-free and endophyte-associated plants and inoculated or not with three AMF species. The biomass of endophyte-free and endophyte-associated plants was increased by AMF inoculation, when growing in soils conditioned by equal endophytic status plants (i.e. home soils). When growing in soils conditioned by plants with different endophytic status, plant biomass was higher than in home soil only in absence of AMF. The content of P and the arbuscular colonization also increased in plants growing in home soils. We demonstrated that AMF shift the intraspecific feedback effects between E+ and E- conspecific plants from negative to positive. Furthermore, we found that the outcome of simultaneous occurrence of foliar and root symbionts on grass performance depends on the matching with the endophytic status of the previous plant.