ARS | Publication request: Bromus tectorum: Variation in Seed Dormancy Among Populations

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 19, 2010
Publication Date: June 20, 2010
Citation: Clements, C.D., Harmon, D.N. 2010. Bromus tectorum: Variation in Seed Dormancy Among Populations [abstract]. Seed Ecology III International Conference.

Technical Abstract: Cheatgrass (Bromus tectorum) is an exotic invasive annual grass that has invaded millions of hectares of rangelands throughout the west. The introduction and invasion of cheatgrass has increased the chance, rate and spread of wildfires. Cheatgrass truncates secondary succession as it outcompetes native perennial grass species for limited resources, primarily moisture. As little as 13 cheatgrass plants/m² can outcompete native perennial grasses. The establishment of long-lived perennial grasses is the best known method at suppressing cheatgrass. Cheatgrass is reported to be primarily dormant at dispersal, and following after-ripening, dormancy is rapidly broken down. Yet there is also strong evidence in the literature for the ability of cheatgrass to build persistent seed banks. We collected cheatgrass seed from five different sites near Reno, Nevada to conduct laboratory germination tests at our Wildland Seed Laboratory. Germination tests were conducted to address three basic questions; 1) cheatgrass seed dormancy at dispersal time, 2) cheatgrass germination following after-ripening requirements, and 3) cheatgrass seed carry-over and germination the following year. Cheatgrass seed was collected from each of the five sites bi-weekly from May 2009 through July 2009. Cheatgrass plant density, seed production and seed bank densities were measured for each population. Germination tests were conducted using 6 temperature regimes (2 C, 5 C, 15 C, 20C, 25 C and alternating 2/15 C) under 5 treatments; 1) within one week of dispersal, 2) 24 weeks after-ripening, 3) 6 weeks at 2 C wet, 4) 6 weeks at 2 C dry and 5) 6 weeks at 40C dry. Tetrazolium tests were conducted for each cheatgrass population to test for viability. Cheatgrass viability was a 95% or more for each population. Cheatgrass germination ranged from 0% to 68% at dispersal time suggesting that cheatgrass is not completely dormant at dispersal time. Cheatgrass dormancy was highest at the constant 25 C, yet this dormancy is lost when germinated at the alternating 2/15 C (2 C for 16 hrs and 15 C for 8 hrs). After-ripening germination rates ranged from 0% to 98% suggesting that even with after-ripening there is a dormancy breaking requirement such as cold-moist-stratification necessary.Cheatgrass seeds that did not germinate under the various dormancy treatments the first year (average 30%), but did germinate the second year ranged from 35% to 69%. This suggests that not only does cheatgrass have the ability to build seed banks for the next year, but also the second year. This is important in the management of rangelands throughout the west as to the degree of innovative weed control practices needed just to suppress cheatgrass densities to levels that seeded species used in restoration efforts have a chance to compete with and establish in these environments.