Decreased colonization rates of invasive species compared to natives by arbuscular mycorrhizal fungi (AMF) have lead to the hypothesis that decreased dependence on mutualists is a key trait for invisibility of a species. However, studies of invasives in their native range show increased levels of colonization. This information coupled with knowledge that mycorrhizal species are not equally beneficial to a single host has led us to hypothesize the decreases of mycorrhizal colonization in invasive species may be due to novel interactions between plants and an AMF makes the association less beneficial for naive hosts. This would reduce host fitness resulting in a reduced fitness on the AMF community, which over many generations may reduce AMF abundance, and possibly allowing the plants to shift from the establishment phase to aggressive expansion. Ten plants of Brachypodium sylvaticum and native Elymus glaucus from five populations in Oregon, USA were sampled for current levels of colonization and spore abundance. Individuals of B. sylvaticum from two invasive populations and the most likely source populations in Europe were grown with and without Oregon AMF innoculum and fertilizer addition to test the potential benefits of mycorhhizae for plant growth.
Results/Conclusions
There was a significant decrease in AMF spore abundance in Oregon soils occupied by invasive rather than native species (p<0.001) providing evidence that this invasive plant may have negative effects of the AMF community. Plants that received inoculation without receiving fertilizer experienced decreased growth while plants that received both AMF and fertilizer had increased growth (p<0.05). European populations experienced the greatest effect on growth due to AMF inoculation though this effect is not significantly different from the invasive regions. Future analysis of colonization and spore data will indicate the level of dependence of B. sylvaticum on AMF for plants from the invaded and native regions.