MSA - Ecology/Pathology
Meyer, Susan E. , Allen, Phil S. , Beckstead, Julie .
Predicting Carryover Seed Bank Density for Cheatgrass (Bromus tectorum).
The winter annual weed Bromus tectorum L. is known for the production of prodigious quantities of seeds. Its seed bank is considered short-lived, but factors mediating seed persistence in soil have not been well-quantified across a range of habitats. We examined seed bank dynamics over a two-year period at five sites that vary in mean annual precipitation from 185 to 528 mm. We use the first year of data to develop a model for predicting viable carryover seed density, and use the second year of data as an independent test of model validity. Carryover seed density at the end of spring is determined by three variables: seed density in the transient fall seed bank, proportion of seeds that germinate, and proportion of potential carryover seeds that are killed, primarily by the fungal seed bank pathogen Pyrenophora semeniperda. Fall seed bank densities are mediated largely by productivity the previous year. This varies tremendously across years and is not closely tied to habitat, as populations at xeric sites may have large seed crops in favorable years, and populations at mesic sites may be infected with systemic smut pathogens that greatly reduce seed set. The fraction of seeds that germinate is largely controlled by the effectiveness of fall and early winter precipitation and tends to be larger at more mesic sites. The fraction of ungerminated seeds that are killed is a function of pathogen inoculum load at the site. More mesic sites, where fewer seeds remain ungerminated in spring, tend to have lower inoculum loads and higher seed survival. Xeric sites have large potential carryover fractions, but also have higher inoculum loads and lower survival. This negative relationship between size of the carryover seed fraction and survival tends to normalize the density of viable carryover seeds, which varies over a relatively small range.
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1 - USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 N 500 E, Provo, Utah, 84606, USA
2 - Department of Plant and Animal Sciences, Brigham Young University, Provo, Utah, 84602, USA
3 - Gonzaga University, Department of Biology, 502 East Boone Avenue, Spokane, Washington, 99258, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood B/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 4:30 PM