Arbuscular Mycorrhizal Fungi In Sage Steppe

Study Site Locations: Camp Guernsey, Wyoming; Piceance Basin, Colorado; Utah.

Arbuscular mycorrhizal fungi (AMF) are root symbionts that have a strong influence on plant interactions by aiding plants in resource acquisition, disease suppression, and tolerance to soil pollution. Just like their plant hosts, AMF have differing degrees of tolerance to environmental variation, such as disturbance regime, soil chemistry and climate. In many systems, plant succession is closely tied to the availability of suitable AMF in the soil, and a reduction in AMFcan slow down replacement of weedy plants by more desirable vegetation.

In western rangelands, the invasion of cheatgrass has been shown to alter AMF in invaded soils, and has led to a semi-permanent steady state whereby the introduced winter annual grass never reverts back to perennial grasslands and shrublands. Although cheatgrass alters AMF, the extent of these alterations have not been documented, the effects of these changes on native vegetation are not known, and the role of these alterations in successional stagnation have not been determined. The goal of our research is to understand how cheatgrass interacts with AMF, what changes occur to the AMF community due to cheatgrass invasion, and how these changes affect native vegetation. Experiments being conducted by REL staff, led by Ryan Busby, include 1) temporal variaton in cheatgrass association with AMF, 2) interactions between native weeds and AMF, 3) diversity of AMF associating with coexisting big sagebrush and cheatgrass,  and 4) utilization of AMF interactions with native weeds for targeted succession in invaded rangelands.  Methods include greenhouse, laboratory/molecular techniques, and field trials.

“Cheatgrass (Bromus tectorum L.) interactions with arbuscular mycorrhizal fungi in the North American Steppe: Prevalence and diversity of associations, and divergence from native vegetation”.  Presented Friday, April 22nd, 2011.Ryan Busby dissertation abstract:

ABSTRACT: Accumulating evidence suggests that plant-microbe interactions play an bimportant role in plant invasion, including arbuscular mycorrhizal fungi (AMF).  Cheatgrass (Bromus tectorum) invasion has been associated with reductions in AMF density and altered AMF colonization in neighboring plant roots. However, specific interactions with AMF, how these interactions differ from native vegetation, and how native vegetation responds to alterations due to cheatgrass have not been investigated. Studies were conducted to measure cheatgrass colonization by AMF throughout its life, identify AMF species associated with cheatgrass, compare AMF diversity between cheatgrass and big sagebrush (Artemisia tridentata), and determine how native plant species interact with AMF in soil invaded by cheatgrass. Cheatgrass was colonized throughout its life by AMF, although colonization was always low. Cheatgrass roots from three sites were colonized by 13 unique AMF DNA sequences. AMF associating with cheatgrass individuals had lower alpha diversity, higher beta diversity, and similar gamma diversity compared to AMF associating with coexisting big sagebrush individuals. Two AMF species associated with big sagebrush more frequently than with cheatgrass. Native plant species were highly variable in their interactions with AMF from an invaded soil. Mutualisms, commensalisms, amensalisms, and parasitisms were all observed. Thus, cheatgrass is a poor host for AMF, modifies the AMF community compared to big sagebrush, and invasion could result in loss of AMF species preferred by big sagebrush. However, some native plant species can rapidly increase AMF density in invaded soils and are highly responsive to the resulting AMF community. This knowledge could improve restoration of invaded soils through focused management of the AMF community.