Investigations of physiological and competitive relationships of Elymus species related to establishment in the Great Basin, USA.

The Great Basin of western North America is rapidly being invaded by exotic annual grasses that decrease cover of native perennial bunchgrasses and shrubs. Bromus tectorum (cheatgrass) is the most widespread and problematic of the annual grass invaders in the Great Basin. Restoration in the Great Basin has had limited success. Restoration success could be related to physiology of native plants in competition for limiting nutrients: Bromus tectorum employs ruderal strategies of resource acquisition, is an effective competitor for water and nitrogen, and can cause mortality of natives in invaded fields as well as prevent establishment of native seedlings. In response to the survival pressure placed on native communities by invaders, natives may experience evolutionary changes. Directional selection for plant traits in restored populations may occur as a result of differential mortality related to the ability to acquire resources. The goal of this research was to determine what physiological traits of native perennial grasses lead to successful establishment under Bromus tectorum competition and to determine if selection for root traits is occurring during restoration. Identification of key plant traits related to establishment and competition is an important step in selecting and breeding plant materials with the best chance of success in restoration. Traits selected during establishment of natives under competition with Bromus tectorum may give insight into the mechanisms of plant establishment. We focus on Elymus elymoides and Elymus multisetus because they have wide geographic ranges and have been identified as good competitors against Bromus tectorum. Results from the first study indicate that different Elymus seed sources had few differences in their physiology and resource acquisition. Bromus tectorum dominated soil water use and nutrient acquisition at the Elymus seedling stage, but was much less effective in competition with mature Elymus plants. Competitive effect of mature Elymus plants on Bromus tectorum was related to water acquisition. Results from the second study show that directional selection for smaller plants with a higher fraction of root biomass occurred in two sites in the Great Basin during seeding of Elymus plants. Together, these results are consistent with selection for traits that allow plants to survive as seedlings in areas of high Bromus tectorum cover, but not consistent with selection for nutrient acquisition or competitive ability with Bromus tectorum. Plant selection for effective restoration of arid rangelands should focus on selecting seedlings for establishment under Bromus tectorum pressure and mature plants capable of inducing competitive effect through water acquisition