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EFFECTS OF AMMONIUM AND NITRATE ON NUTRIENT UPTAKE AND ACTIVITY OF NITROGEN ASSIMILATING ENZYMES IN WESTERN HEMLOCK
Citation:
Knoepp, J., D. Turner, AND D. Tingey. EFFECTS OF AMMONIUM AND NITRATE ON NUTRIENT UPTAKE AND ACTIVITY OF NITROGEN ASSIMILATING ENZYMES IN WESTERN HEMLOCK. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-93/424.
Description:
Western hemlock seedlings were grown in nutrient solutions with ammonium, nitrate or ammonium plus nitrate as nitrogen sources. he objectives were to examine (1) possible selectivity for ammonium or nitrate as an N source, (2) the maintenance of charge balance during ammonium and nitrate uptake, and (3) the activity of the nitrogen assimilating enzymes, nitrate reductase, glutamine synthetase, and glutamine dehydrogenase, in relation to the uptake of different nitrogen sources. he uptake studies revealed that western hemlock takes up ammonium faster than nitrate and that ammonium partially inhibits nitrate uptake. fflux of H+, 1.26 ueq H+/ueq NH+4, occurred to maintain charge balance in plants utilizing ammonium nitrogen whereas potassium served as a counter ion in the uptake of nitrate. itrate reductase activity varied with nitrate availability in root tissue, but showed no response in needles, indicating that most nitrate in reduced in the roots. here was no glutamine synthase response to differing nitrogen sources or uptake rates in root tissue, and little response in needles. lutamate dehydrogenase activity in root tissue varied significantly with nitrogen source, being greatest in treatments containing ammonium. esults indicate that western hemlock may be adapted to sites where NH+4 is the predominate N source.