ARS | Publication request: Drought tolerance in two perennial bunchgrasses used for restoration in the Intermountain West, U.S.A.

Submitted to: Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 23, 2010
Publication Date: March 7, 2011
Citation: Mukherjee, J.R., Jones, T.A., Adler, P.B., Monaco, T.A. 2011. Drought tolerance in two perennial bunchgrasses used for restoration in the Intermountain West, U.S.A. Plant Ecology. 212:461-470.

Interpretive Summary: Seedling establishment is the most vulnerable life stage of rangeland perennial bunchgrasses such as bluebunch wheatgrass and Snake River wheatgrass. Downy brome, an invasive annual weed in the Intermountain West, germinates in the fall and preempts early-season abundant-soil resources from bunchgrass seedlings, which do not germinate until spring. We found that immature seedlings of bluebunch wheatgrass exhibited highshoot and root biomass and high shoot length, likely advantageous in high-resource environments. In contrast, Snake River wheatgrass's display of high specific leaf area (SLA; leaf area per unit biomass) and high specific root length (SRL; root length per unit biomass) is suggestive of faster growth and greater resource-extraction capability, likely advantageous in resource-limited environments. The high root length of downy brome may be responsible for its ability to preempt early-season soil resources, ensuring its successful establishment. Our results suggest that native perennial plant materials with greater root length or SRL may prove beneficial for seedling establishment under competitive rangeland conditions.

Technical Abstract: The success of Bromus tectorum L., an invasive winter annual grass of North America's Intermountain West, has been attributed to its early germination, superior cold-temperature growth, profuse root production, and high specific leaf area (SLA). To better understand B. tectorum's success with respect to seed germination, seeding morphological traits, and growth rates, we compared it to two perennial rangeland bunchgrasses native to the region, Pseudoroegneria spicata (Pursh) A. Love, and Elymus wawawaiensis J. Carlson & Barkworth. In addition, we sought to compare commercially available plant materials of these native species for seedling-growth characteristics and to identify perennial-grass traits that likely contribute to successful seedling establishment. To accomplish these objectives, we compared B. tectorum to three commercially available P. spicata populations ('Whitmar', 'Goldar', and Anatone germplasm) and 'Secar' E. wawawaiensis at the immature seedling stage under cold (5/10 degrees C) and more favorable (15/20 degrees C) day/night temperatures. At this early stage, our data suggest that a substantial investment in root surface area, rather than high shoot length or SLA, may account for B. tectorum's success. Pseudoroegneria spicata, in particular Anatone germplasm, exhibited highest shoot biomass, root biomass, shoot length, and absolute growth rate. However, E. wawawaiensis displayed highest SLA at both temperatures and highest specific root length (SRL) at low temperature, despite displaying the lowest shoot and root biomass. Although P. spicata's greater productivity makes for better seeding establishment, it also may prove disadvantageous in competitive or highly resource-limited environments where high SRL could be advantageous.