| Summary: | Many grasses are simultaneously symbiotic with <i>Epichloë</i> fungal endophytes and arbuscular mycorrhizal fungi (AMF). <i>Epichloë</i> endophytes are a group of filamentous fungi that colonize and grow within aerial plant tissues, such as leaves and stems. Infection and hyphal growth of <i>Epichloë</i> endophytes confer fitness advantages to the host plants. In addition to producing fungal alkaloids and altering host metabolic/genetic profiles, it is proven that symbiosis of plants with root/foliar endophytes affects the plant–soil relationship. We propose that the <i>Epichloë</i> presence/infection results in variations of soil and root AMF through allelopathic effects. We performed a meta-analysis that integrated the allelopathic effects of <i>Epichloë</i> endophytes on grass–AMF development. In the pre-symbiotic phase of grass–AMF symbiosis, root exudation from <i>Epichloë</i>-infected plants positively affected AMF growth, whereas the shoot exudates of <i>Epichloë</i>-infected plants inhibited AMF growth. In the symbiotic phase of grass–AMF symbiosis, the <i>Epichloë</i> infection was found to reduce root mycorrhizal colonization in plants. No pattern in the response of soil AMF to <i>Epichloë</i> presence was found. This study should improve our understanding of the impact of <i>Epichloë</i> endophytes on belowground microbial symbionts within the same host plant. Grass–<i>Epichloë</i>–AMF symbiosis may become an important model for studying above–belowground interactions.
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