Allen, Phil S. , Meyer, Susan E. , Merrill, Katherine T. .
Comparing Thermal After-ripening Patterns for Seeds of Two Invasive Annual Brome Grasses.
Weedy winter annual brome grasses (Bromus spp.) have displaced millions of hectares of native vegetation in the semiarid western United States. Extensive studies on cheatgrass (B. tectorum L.), the dominant invader of cool desert/shrub steppe ecosystems in this region, have shown that seed populations exhibit varying levels of primary dormancy at maturity. Dormancy loss during dry storage for B. tectorum can effectively be modeled using thermal after-ripening time (i.e., linear accumulation of thermal-time units above a base temperature). In the present study, we use a similar approach to characterize seed dormancy loss in red brome (B. rubens L.), which is a primary invader of many warm desert ecosystems. Dormancy loss of B. rubens seeds in dry storage can also be described using thermal time models. However, seeds of B. rubens have a generally longer thermal time requirement for complete dormancy loss than seeds of B. tectorum. The seeds of B. rubens also have a low optimum germination temperature (<15C) that does not increase during dormancy loss, and they germinate more slowly than the seeds of B. tectorum at optimum temperature even when fully after-ripened. Thus, germination of B. rubens seeds is subject to more ecological constraints than germination of B. tectorum seeds. The ecological relevance of this germination strategy for B. rubens is readily apparent. The harsher seedling establishment environment present in warm desert ecosystems requires a more conservative germination strategy in order to maximize the probability for seedling establishment success. This conclusion is supported by the fact that at least one B. tectorum genotype that is highly successful in warm deserts has a germination strategy that approaches the strategy of B. rubens.
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1 - Department of Plant and Animal Sciences, Brigham Young University, Provo, Utah, 84602, USA
2 - USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 N 500 E, Provo, Utah, 84606, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood A/Snowbird Center
Date: Monday, July 27th, 2009
Time: 9:15 AM