Root Length, Leaf Area, and Biomass of Crested Wheatgrass and Cheatgrass Seedlings

Abstract

Cheatgrass (Bromus tectorum L.) dominates large tracts of rangeland in the western United States. Previous research has demonstrated the competitive nature of this species; however, the mechanisms contributing to its dominance have not been well elucidated. It is often suggested that cheatgrass outcompetes perennial seedlings because it germinates and grows at lower soil temperatures. However, even in studies where temperatures are not limiting, cheatgrass outcompetes perennial seedlings. Therefore, I conducted a study to compare accumulation of root length, leaf area, and biomass of cheatgrass and crested wheatgrass (Agropyron desertorum (Fisch. ex Link) Schult. cv. Nordan) seedlings under non-limifting conditions. Seedlings were grown in pots in the greenhouse for 60 days post-sowing. There were 4 seedlings per pot, and sampling was conducted weekly at 24-60 days after sowing. Maximum and minimum temperatures were 28? C and 40 C, respectively, and plants were watered twice a week. Cheatgrass had greater root length density and leaf area than crested wheatgrass, especially during the later samplings. For the last 2 samplings, cheatgrass averaged about 12% more root mass and 56% more shoot mass, yet had more than twice the root length and leaf area of crested wheatgrass. Cheatgrass was more efficient (per unit of biomass) in producing leaf area and root length, which helps explain its ability to quickly become established and exploit soil nutrient and moisture reserves.