Perennial grass seedlings modify biomass and physiological traits in response to an annual grass neighbor

Authors: Jones, Thomas; BELL, B - Utah State University; Monaco, Thomas

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2021
Publication Date: 5/17/2021
Citation: Jones, T.A., Bell, B.P., Monaco, T.A. 2021. Perennial grass seedlings modify biomass and physiological traits in response to an annual grass neighbor. Rangeland Ecology and Management. 77:93-100. https://doi.org/10.1016/j.rama.2021.04.001.
DOI: https://doi.org/10.1016/j.rama.2021.04.001

Interpretive Summary: Downy brome is an invasive annual grass that is pervasive on rangelands in the Intermountain West. This weed damages ecosystems by facilitating the loss of soil nutrients and fueling recurrent wildfires, thereby hindering desirable perennial vegetation. The establishment of perennial vegetation through seedling is needed to reclaim downy brome-infested lands, but establishment of slow-growing perennials is difficult in the presence of this highly competitive weed. We grew seedlings of populations of two desirable perennial grasses, bluebunch wheatgrass and Snake River wheatgrass, in the presence of downy brome in three greenhouse trials, two in winter and one in summer. A single downy brome seedling reduced the shoot dry-matter of a single perennial seedling about 30% overall in all three trials. While some perennial populations fared better than others, this varied by trial. In response to downy brome, perennials partially closed their stomata and increased the tension with which they held their internal water in the winter trials, but in the summer trial, competition from downy brome for nitrogen may have limited perennial growth. More effective populations of these perennial species will be needed to recover lands impacted by downy brome.

Technical Abstract: We conducted three greenhouse trials, two in the winter and one in the summer, to evaluate the performance of populations of bluebunch wheatgrass (BBWG; Pseudoroegneria spicata [Pursh] A. Love) and Snake River wheatgrass (SRWG; elymus wawawaiensis J. Carlson & Barkw.). A single seedling of either of these two perennial grasses was grown with or without competition from a single seedling of the invasive annual, downy brome (DB; Bromus tectorum L.). After five weeks, DB had reduced perennial shoot dry-matter (DM) 23-42% across the three trials. The DB treatment x population interaction for shoot DM was inconsistent among the three trials, suggesting that the environments of the three trials were dissimiliar. In the winter trials, DB reduced stomatal conductance and xylem pressure potential, suggesting it induced drought stress. Howevver, in the summer trial, DM had no effect on these parameters, suggesting that DB competition was related to some unmeasured variable, perhaps N concentration. Averaged across the two winter trials, DB reduced SRWG shoot DM more than BBWG (31.8% vs. 27.6%), but in the summer trial, the reverse occurred with DB reducing BBWG shoot DM more than SRWG (41.9% vs. 22.9%). Through stomatal, conductance was consistently higher and xylem pressure potential was consistently more negative for BBWG than SRWG, BBWG exceeded SRWG in shoot DM for four of five comparisons (all except the DB treatment in the summer trial). Compared to older cultivars, newer plant materials tended to produce less shoot DM, suggesting a more conservative growth strategy. The sizeable reduction in perennial shoot DM induced by a single DB competitor plant suggests that seedlings of these native plant materials would be highly susceptible to DB competition in a rangeland seeding.