Date of Award:


Document Type:


Degree Name:

Master of Science (MS)




Christopher A. Call


Screening populations for development into released plant materials can be done inexpensively and in a timely manner. A common approach has been to quantify the amount of shoot dry mass produced as a surrogate for competitiveness. Besides dry mass production , other morphological characteristics have been employed , but physiological parameters have received less emphasis. Dry mass production may be an important characteristic, but identifying the traits responsible can be just as imperative . Populations with greater drought tolerance may be less impacted by competition for water from weeds, which could lead to greater establishment of desirable grasses on disturbed landscapes.

The objective for chapter 2 was to evaluate the effects of cheatgrass competition on the growth and water relations of three Snake River wheatgrass (Elymus wawawaiensis) populations and two bluebunch wheatgrass (Pseudoroegneria spicata) populations in the seedling stage in a greenhouse setting. The treatments were 1) containers with a single wheatgrass plant or 2) containers with one wheatgrass and one cheatgrass plant. Containers were watered gravimetrically to 11.5% soil-water content, regard less of treatment, every few days until harvested on day 35. Cheatgrass competition reduced root dry mass, shoot dry mass, leaf area, leaf number, tiller number, xylem pressure potential, and stomata} conductance. The bluebunch wheatgrass populations generally had more negative xylem pressure potential, higher stomata! conductance, and higher shoot dry mass, while the Snake River populations had higher specific leaf area and less negative xylem pressure potentials .

The objective for chapter 3 was to evaluate the effects of planting density on the growth and water relations over a 2-year period among five Snake River wheatgrass populations, one thickspike wheatgrass (Elymus lanceolatus) population , and three interspecific hybrids. High (25 plants/m 2 ) and low-density (7.8 plants/m2) plots of each grass were transplanted to Millville, Utah in the spring of 2005 and 2006 intended to generate low and high resource availability environments, respectively. Thickspike wheatgrass had the highest shoot dry mass and least negative xylem pressure potential , the hybrids were intermediate, and the Snake River wheatgrasses were least productive and more water stressed.

The primary benefit of this thesis will be through identifying the potential for developing these populations into improved plant materials and releasing them for commercial use in degraded rangelands across the Intermountain West. These new plant materials may also help transition damaged rangelands towards more desirable stable states composed of lower abundances of invasive annual grasses.