PARENT SESSION
Poster Session 7: Invasive Species.

Monday, August 2 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.

Vesicular-arbuscular mycorrhizae in cheatgrass (Bromus tectorum) and two native bunch grasses on the Colorado plateau.

DeMarco, Bethany ^*,, Sanford, Robert,

ABSTRACT- Cheatgrass (Bromus tectorum) is a highly invasive competitor that threatens native species. The competitive mechanisms belowground that allow B. tectorum success in new ecosystems have been studied minimally. Vesicular-arbuscular mycorrhizae (VAM) allow plants to access additional nutrients, and the possibility of a facultative association between B. tectorum and VAM fungi is likely and potentially important. The main objective of this research is to determine if B. tectorum and two native grasses, Hilaria jamesii and Stipa oryzopsis , are associated with mycorrhizal fungi under grazed and ungrazed conditions on the Colorado Plateau. Ten root samples of each grass species, B. tectorum, H. jamesii, and S. oryzopsis, were collected from 2 grazed and 2 ungrazed sites. The ungrazed sites were collected within Canyonlands National Park and the grazed sites are located near the Park boundary, on BLM land. Roots were cleared and stained for mycorrhizal cells in the root segments. The roots were viewed microscopically to detect stained fungi, and were quantified by measuring the percent of the root that is infected. A significant interaction occurred for percent mycorrhizal infection between treatment and species (P<.0001); both B.tectorum and H. jamesii exhibited an increase in infection in ungrazed sites (P<.05, P<.0001, respectively), whereas S. oryzopsis showed a significant decrease in percent infection in ungrazed sites (P<.01). The interaction of mycorrhizal infection between grass species and site treatments has important implications. Previously B. tectorum has been shown to have a facultative relationship with VAM fungi (Allen, unpublished). Our data suggest that this invasive grass does not gain a competitive advantage over native grasses from association with VA mycorrhizae. In contrast to S. oryzopsis, an increase in infection of both B. tectorum and H. jamesii supports the hypothesis that grazing reduces VAM fungal colonization for some grass species.

Key words: colorado plateau, desert grassland, mycorrhizae, bromus tectorum