Siemens, J. Aurea , Zwiazek, Dr. Janusz .
Nitrogen metabolism, assimilation, and water relations in ectomycorrhizal Populus tremuloides.
In controlled experiments, trembling aspen (Populus tremuloides) has been shown to exhibit symptoms of ammonium toxicity at low concentrations. However, P. tremuloides is one of the dominant tree species of mixedwood boreal forest where ammonium is the main form of nitrogen available to plants. In the present study, we examined the hypothesis that the ectomycorrhizal fungi play a significant role in conferring ammonium tolerance to P. tremuloides. Physiological experiments were conducted to better understand some of the mechanisms by which P. tremuloides is able to tolerate the presence of ammonium alone and in combination with nitrate. Seedlings were inoculated with ectomycorrhizal fungi (Hebeloma crustuliniforme) and used in several studies examining water relations, xylem and soil pH, nitrogen uptake, and nitrogen metabolism. Results indicated that activity of glutamine synthetase (GS), a key enzyme in ammonium assimilation, was higher in roots and leaves of mycorrhizal seedlings, which was consistent with the nitrogen analysis of tissue and xylem exudate. Additionally, the optimal pH for root water flux was slightly higher in mycorrhizal seedlings, and the pH of soil leachate from mycorrhizal seedlings was most similar to that of xylem pH compared to non-mycorrhizal seedlings. These results suggest that mycorrhizal fungi may allow for greater ammonium tolerance in P. tremuloides by altering the physiological processes that allow for increased ammonium assimilation.
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1 - University of Alberta, Renewable Resources, 4-42 Earth Sciences Bldg., Edmonton, Alberta, T6G 2E3, Canada
2 - University of Alberta, Renewable Resources
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM