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Abstract Detail


Symbioses: Plant, Animal, and Microbe Interactions

Baughman, Owen W. [1], Meyer, Susan E. [2].

Investigating Bromus tectorum die-offs in Great Basin cold deserts: Quantification of the pathogen Pyrenophora semeniperda.

The invasive annual grass Bromus tectorum occurs in monocultures across large areas of the semiarid West. A frequent phenomenon in B. tectorum monocultures is the presence of ‘die-offs’, areas where this grass suddenly fails to establish and produce seeds. Our study explored the role of the pathogen Pyrenophora semeniperda in B. tectorum die-offs. This pathogen can kill most dormant and slow-germinating B. tectorum seeds in the spring seed bank and may also cause mortality of non-dormant seeds. We combined field observations with seed bank studies to quantify B. tectorum stand characteristics, seed carryover, and P. semeniperda-caused seed mortality at ten die-off sites across the Great Basin. Each die-off was compared with an adjacent control where B. tectorum had a healthy current-year seed crop. If P. semeniperda were a causal agent in a recent die-off, we would expect higher densities and proportions of P. semeniperda-killed seeds in die-off areas. We found that in seven of ten sites, total seed bank densities were significantly higher in the controls, suggesting that the die-off was not recent. Six of these sites also showed significantly higher viable carryover seed density in the controls. Four had lower densities but significantly higher proportions of P. semeniperda-killed seeds in die-offs. Thus, there was little direct evidence supporting P. semeniperda as a causal agent in these older die-offs. The other three sites did not have significantly different total seed, P. semeniperda-killed seed, or viable carryover seed densities between controls and die-off areas. This indicated that die-off events were in their first year, but again produced no evidence for P. semeniperda as a causal factor. While failing to detect any clear role for P. semeniperda in the die-off phenomenon, this study has demonstrated a methodology for determining the age of a B. tectorum die-off based on seed bank data.


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1 - University of Idaho College of Natural Resources, Natural Resource Ecology, PO Box 441142, Moscow, ID, 83844-1142, United States of America
2 - USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 N 500 E, Provo, Utah, 84606, USA

Keywords:
Bromus tectorum
Pyrenophora semeniperda
die-off
cheatgrass
Great Basin
seed bank .

Presentation Type: Poster:Posters for Topics
Session: P1
Location: Event Tent/Cliff Lodge
Date: Monday, July 27th, 2009
Time: 5:30 PM
Number: P1SY001
Abstract ID:263


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