Intraspecific Variation in the Response of \u3ci\u3eElymus Elymoides\u3c/i\u3e to Competition from \u3ci\u3eBromus Tectorum\u3c/i\u3e

Native plant materials are often seeded to restore biodiversity and ecosystem function in areas overtaken by exotic weeds. Plant materials are evaluated on intraspecific differences in productivity and expression of traits advantageous to establishment (e.g., phenology, seed mass, and growth rate); some investigations also consider population-level adaptation to exotic species. However, there is a lack of studies that broadly evaluate response to competition from exotic species at multiple scales within a species. In a greenhouse experiment, we used analysis of variance to assess the growth response of a perennial grass native to the Intermountain West, (Elymus elymoides), to competition from a common invasive species, (Bromus tectorum), at three levels of intraspecific differentiation: subspecies, lineage (wild vs. domestic germplasm), and population. We used regression analysis to assess whether E. elymoides populations from highly invaded areas were less affected by B. tectorum competition. Finally, we explored the relationship between growth traits and competitive response using random forest regression. We found significant differences among E. elymoides subspecies in their response to B. tectorum competition, no difference between wild and domestic lineages, and no population-level differentiation within subspecies. Field abundance of B. tectorum had a significant positive relationship with E. elymoides biomass, but not competitive response, suggesting that E. elymoides has not adapted to the invader. Elymus elymoides plants which were less affected by competition were smaller, allocated more biomass to leaves, and had fewer fine roots, suggesting that light interception and tissue retention were prioritized by seedlings in this competitive greenhouse environment