Interactive effects of co-occurring epichloid endophytes, rhizobia and arbuscular mycorrhizal fungi modulating their benefits to grasses and legumes.

Abstract Symbiotic interactions are very extended in nature and their multiple co-occurrence among plants, fungi and bacteria is highly likely within a community. Thus, a single plant can harbour different strains, species or types of symbionts. Furthermore, at the neighbourhood level, the co-occurrence of grasses and legumes is a frequent event associated with their specific (endophyte, rhizobia) or generalist (arbuscular mycorrhizal fungi) symbionts. The simultaneous presence of two symbionts may induce additive or interactive effects (i.e. synergisms or antagonisms) both at plant and neighbourhood level. In this chapter, we explore the responses of plants when two symbionts are present within the same host or within neighbouring plants. Here we review studies researching the effects of epichloid endophytes and systemic and asymptomatic fungal symbionts of grasses on colonization of arbuscular mycorrhizal fungi (AMF) and their consequences on host plant performance. Also, we explore the current knowledge related to the presence of epichloid endophyte and AMF on the host grass affecting legume-rhizobia interaction, whether coexisting in the neighbourhood or growing after grass dies. Interestingly, endophyte effects go beyond the host and impact on other symbioses, either within the host or established in co-occurring plants in the neighbourhood. Endophytes either increase or impair AMF colonization within the host, and both symbionts can have interactive or additive effects on host performance, depending on the grass, endophyte and AMF species, and on the abiotic and biotic environment. Furthermore, endophyte presence on the host grass can affect different attributes at community level through altering the performance of a neighbouring legume, or one that grows after grass dies. As an outcome, the effects of these specific symbionts can result in potential public benefits for non-host plants through the propagation of interactive effects of several symbionts to the whole symbiosis influence area, the symbiosphere. The benefits give rise to the appearance of agroecosystem processes or services that could favour their sustainability.