Symbiotic interactions between plants and microorganisms have recently become the focus of research on biological invasions. However, the interaction between different symbionts and their consequences in host-plant invasion have been seldom explored. Here, we propose that vertically transmitted fungal endophytes could reduce the dependency of invasive grasses on mycorrhizal fungi allowing host establishment in those environments where the specific mutualist may be not present. Through analyzing published studies on nine grass species, we evaluated the effect of seed-borne Epichloë endophytes on the relationship of invasive and non-invasive grasses with arbuscular mycorrhizal fungi (AMF), a symbiosis known to be fundamental for plant fitness and invasion success. The endophyte effect on AMF colonization differed between invasive and non-invasive grasses, reducing mycorrhization only on invasive species but with no impact on their biomass. These results allowed us to propose that Epichloë endophytes could reduce the dependency of host plants on the mutualism with AMF, promoting host grass establishment and subsequent invasion. Simultaneous interactions with different types of mutualists may have profound effects on the host-plant fitness facilitating its range expansion. Our findings suggest that some specific mutualistic fungi such as epichloid endophytes facilitate host invasion by reducing the requirements of the benefits derived from other mutualisms.

植物和微生物之间的共生相互作用最近成为生物入侵研究的重点。然而，很少探索不同共生体之间的相互作用及其在宿主植物入侵中的后果。在这里，我们建议垂直传播的真菌内生菌可以减少入侵草对菌根真菌的依赖，从而允许在可能不存在特定共生者的环境中建立宿主。通过分析已发表的关于九种草的研究，我们评估了种子传播的Epichloë内生菌关于侵入性和非侵入性草与丛枝菌根真菌 (AMF) 的关系，AMF 是一种已知对植物健康和入侵成功至关重要的共生关系。内生菌对 AMF 定植的影响在侵入性和非侵入性草种之间有所不同，仅减少入侵物种的菌根形成，但对其生物量没有影响。这些结果使我们能够提出Epichloë内生菌可以减少寄主植物对与 AMF 共生的依赖，促进寄主草的建立和随后的入侵。与不同类型的互惠者同时相互作用可能对寄主植物适应性产生深远的影响，促进其范围的扩大。我们的研究结果表明，一些特定的共生真菌，如表皮内生菌，通过减少对其他共生所带来的好处的需求来促进宿主入侵。