ARS | Publication request: Effects of maternal environment on cheatgrass seed dormancy

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 5, 2011
Publication Date: February 1, 2012
Citation: Harmon, D.N., Clements, D.D., Young, J.A. 2012. Effects of maternal environment on cheatgrass seed dormancy. In: Proceedings of Society for Range Management, January 29-February 3, 2012, Spokane, Washington. 65:46.

Technical Abstract: One of the greatest advantages cheatgrass (Bromus tectorum) has is building large seed banks. Seed banks can persist during self dominance, post fire, post herbicidal control and healthy plant communities. There are numerous reasons a seed does not germinate, primarily being a lack of moisture. However, even with adequate moisture a state of seed dormancy can prevent germination. Two major types of primary dormancy exist, exogenous and endogenous. Cheatgrass is usually observed as endogenous or caused by conditions within the embryo. After-ripening, a period of time when germination inhibitors break down, can lead to cheatgrass seeds being exceedingly non-dormant. Non-dormant seeds have the ability to germinate during fall, winter, spring and summer in northwestern Nevada. Cheatgrass can also acquire a secondary dormancy when non-dormant seeds go through an overwinter process of freeze-thaw and wet-dry. This leads to a continuous germination strategy, a clear advantage in harsh unpredictable environments. The objective of this research was to document variability in seed dormancy of cheatgrass populations dominating wide-ranging plant communities within the same northwestern Nevada watershed. Cheatgrass seed dormancy has been found to be variable between and among populations, asking the question; is dormancy bound by an adapted genetic code or determined by the conditions during seed maturation? Summer germination is thought of as a risk at best increasing selective pressure for seed dormancy. Population comparisons often examine wide geographic/climate comparisons, opening the door for confounding factors. This can lead to rudimentary explanations of multiple exotic introductions. In order to focus on environmental prediction indicators, we sampled from differing plant communities in the same climatic ecosystem. We hypothesized that 1) summer germination, 2) plant size as a function of resource availability, and 3) soil moisture can predict seed dormancy. In 2010-2011 we located 15 cheatgrass populations within the Truckee watershed of northwestern Nevada. Five commonly invaded plant communities were identified 1) Wyoming big sagebrush (Artimesia tridentata ssp. wyomingensis), 2) post-burn cheatgrass, 3) sandy soil salt desert, 4) black greasewood (Sarcobatus vermiculatus)/silt soil salt desert, and 5) Jeffery pine (Pinus jefferyi) community. At each site we collected, short (<10cm plant), tall (>30cm plant) and random sized parent seed samples (3 samples each >20 plants >30 m apart). Germination was tested pre/post after-ripening (<6 weeks, >16 weeks) at four temperatures (2C, 15C, 25C and 2/15C alternating). Dormancy percent was ranked by plant community at 25C pre-post after-ripening. Both salt desert communities ranked the highest (86% and 63% dormant pre-post) followed by post-burn cheatgrass (75% and 54%). Wyoming big sagebrush and pine forest ranked the lowest (55% and 37%). Summer germination occurred at the salt desert sites making it a possible predictor of dormancy. Small plants exhibited slightly increased dormancy (short 76%, random 71%). Lower soil moisture also corresponded to increased dormancy between populations and years; May 2011 soil moisture by site (sandy salt desert 0.75%, post burn 1.5%, greasewood 1.7%, big sagebrush 4.2% and Pine forest 17.7%) and by year (i.e. greasewood; 2010 = 4.8% moisture-84% dormant verses 2011 = 1.7% moisture-94% dormant) indicating a possible stress response of physiological dormancy. Based on our observations it is likely that the maternal environment effects cheatgrass seed dormancy.