Allelopathic Effects of Foliar Epichloë Endophytes on Belowground Arbuscular Mycorrhizal Fungi: A Meta-Analysis

Many grasses are simultaneously symbiotic with Epichloë fungal endophytes and arbuscular mycorrhizal fungi (AMF). Epichloë 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 Epichloë 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 Epichloë presence/infection results in variations of soil and root AMF through allelopathic effects. We performed a meta-analysis that integrated the allelopathic effects of Epichloë endophytes on grass–AMF development. In the pre-symbiotic phase of grass–AMF symbiosis, root exudation from Epichloë -infected plants positively affected AMF growth, whereas the shoot exudates of Epichloë -infected plants inhibited AMF growth. In the symbiotic phase of grass–AMF symbiosis, the Epichloë infection was found to reduce root mycorrhizal colonization in plants. No pattern in the response of soil AMF to Epichloë presence was found. This study should improve our understanding of the impact of Epichloë endophytes on belowground microbial symbionts within the same host plant. Grass– Epichloë –AMF symbiosis may become an important model for studying above–belowground interactions.