Suppression of cheatgrass by perennial bunchgrasses

Authors: BLANK, ROBERT - Retired ARS Employee; Clements, Darin - Charlie; MORGAN, TYE - Bureau Of Land Management; Harmon, Daniel - Dan; Allen, Fay

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2020
Publication Date: 11/13/2020
Citation: Blank, R.R., Clements, D.D., Morgan, T., Harmon, D.N., Allen, F.L. 2020. Suppression of cheatgrass by perennial bunchgrasses. Rangeland Ecology and Management. 73(6):766-771. https://doi.org/10.1016/j.rama.2020.04.004.
DOI: https://doi.org/10.1016/j.rama.2020.04.004

Interpretive Summary: Biological suppression is critical to long-term control of the invasive annual grass, cheatgrass. We compared the ability of a non-native grass (‘Hycrest’ crested wheatgrass) and two native grasses (Snake River wheatgrass and bluebunch wheatgrass) to suppress cheatgrass. All perennial grasses suppressed cheatgrass; however, crested wheatgrass was superior. A combination of reduced nitrogen availability, occupation of soil space by perennial roots, and attenuation of the nitrogen cycle were all factors in perennial grass suppression of cheatgrass.

Technical Abstract: Long-term control of the invasive annual grass, cheatgrass, is predicated on its biological suppression. Perennial grasses, which have been shown to effectively suppress cheatgrass, vary in their suppressive ability. We compared the ability of a non-native grass (‘Hycrest’ crested wheatgrass) and two native grasses (Snake River wheatgrass and bluebunch wheatgrass) to suppress cheatgrass. In a greenhouse in separate tubs, 5 replicates of each perennial grass was established for 96 days upon which two seeds of cheatgrass were then sown at distances of 10, 30, and 80 cm from the established plants. Water was not limiting to growth of cheatgrass. After 60 days growth, cheatgrass plants were harvested, dried, weight recorded, and tissue C and N quantified. Soil N availability was quantified at each location where cheatgrass was sown, both before sowing and after harvest. Relative to cheatgrass grown at 80 cm, all perennial grasses significantly reduced aboveground biomass at 30 cm (68% average reduction) and at 10 cm (98% average reduction). Sown at 10 cm from established perennial grasses, cheatgrass aboveground biomass was inversely related with perennial grass root mass per unit volume of soil. All cheatgrass sown at 10 cm from ‘Hycrest’ crested wheatgrass died within 38 days. Before sowing of cheatgrass, soil 10 cm from established perennial grasses had significantly less mineral N than soil taken at 30 and 80 cm. Relative to cheatgrass tissue N for plants grown at 80 cm, cheatgrass nearest to the established perennial grasses contained significantly less tissue N. All perennial grasses inhibited the NO2- to NO3- nitrification step; for ‘Hycrest’ crested wheatgrass, soil taken at 10 cm from the plant had a molar proportion of NO2- in the NO2- + NO3- pool of greater than 90%. In summary, a combination of reduced nitrogen availability, occupation of soil space by perennial roots, and attenuation of the nitrogen cycle all contributed to suppression of cheatgrass. Interpretive Summary: Biological suppression is critical to long-term control of the invasive annual grass, cheatgrass. We compared the ability of a non-native grass (‘Hycrest’ crested wheatgrass) and two native grasses (Snake River wheatgrass and bluebunch wheatgrass) to suppress cheatgrass. All perennial grasses suppressed cheatgrass; however, crested wheatgrass was superior. A combination of reduced nitrogen availability, occupation of soil space by perennial roots, and attenuation of the nitrogen cycle.