Effects of invasive and native grassland plant species on diversity and composition of associated communities of arbuscular mycorrhizal fungi

Background/Question/Methods

Many grasslands are currently experiencing invasions by exotic plant species. Invasive species have the potential to alter the diversity and composition of mycorrhizal fungal communities both directly, by serving as hosts for a particular subset of the fungal community, and indirectly, through affecting the colonization of native hosts by mycorrhizal fungi. Depending on the nature of these changes, they could act to suppress native plants, reinforce invasions and interfere with re-establishment of native grasslands even after effective management of invasive species. In previous experimental work, we found that a legacy of soil occupancy by invasive perennials reduced growth of native perennial seedlings. In this study, we tested the hypotheses that (1) diversity and composition of arbuscular mycorrhizal fungi (AMF) differ between roots of native and exotic perennial hosts and (2) diversity and composition of arbuscular mycorrhizal fungi in roots differ between soils conditioned by native and exotic perennial plant species. Three invasive perennials (crested wheatgrass, Agropyron cristatum; leafy spurge, Euphorbia esula; and smooth brome, Bromus inermis), three native perennials (blue grama, Bouteloua gracilis; Lewis’ flax, Linum lewisii; green needlegrass, Nassella viridula), and a native perennial species mixture were grown separately through three three-month cycles of soil conditioning in the greenhouse, after which twelve plant species (six natives and six exotics) were grown together for an additional cycle. We subsequently identified AMF in roots using T-RFLP.

Results/Conclusions

In general, native plants were more likely to be colonized by AMF and exhibited a greater richness of AMF per root sample than invasive plants. Invasive soil conditioning did not reduce AMF richness or affect colonization levels, but did alter the taxonomic composition of mycorrhizal associations. Our results suggest that over time invasive plant species will restrict the diversity of AMF communities in grasslands in ways that may be detrimental to maintenance of native plant species.