Graduate Thesis Or Dissertation
 

Mycological Maintenance of Rangelands and the Impacts of a Thatch Forming Invasive Annual Grass (Taeniatherum caput-medusae)

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  • Arbuscular mycorrhizal fungi (AMF) may exert profound influences on ecosystem resilience and invasion resistance in western North American sagebrush steppe and other arid rangeland plant communities. Maintenance of plant community structure through ecological feedbacks such as facilitation of nutrient cycling and uptake by host plants, physical and chemical contributions to soil structural stability, and mediation of plant competition suggest AMF may act as keystone facilitators in stressful arid environments. A review of the existing scientific literature highlights the relevance to AMF in sagebrush steppe rangelands, with specific focus on impacts of land management, disturbance, and invasion on AMF communities. A mycologically-based approach to invasive plant management is proposed, based on an example root AMF analysis of the native perennial bunchgrass Pseudoroegneria spicata and the exotic invasive annual grass Taeniatherum caput-medusae along an invasion gradient in eastern Oregon. This example demonstrates AMF colonization of the foundation bunchgrass species and limited colonization of the annual grass, at least in the sitestudied. Taeniatherum caput-medusae may effect colonization rates of dark septate endophytes in the roots of neighboring P. spicata, although direction of influence varied between years. Hypothesis testing of possible effects of T. caput-medusae on soil structure and function was explored, finding correlations between increasing invasive plant cover, and increased soil moisture levels during periods of high soil moisture (i.e. April). During drought periods a relationship was only visible on one of three research hills, with increased invasive cover correlating with decreases in soil moisture percentage. Influences of soil texture on site invasibility is discussed, along with possible long term effects of a thatch-forming invasive annual grass with limited mycorrhizal colonization, and recommendations are made for future research.
  • Keywords: rangeland, mycorrhizae, bluebunch wheatgrass, DSE, invasion, AMF, medusahead, resilience
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