Effects of ammonium and nitrate on nutrient uptake and activity of nitrogen assimilating enzymes in western hemlock
Abstract
Western hemlock seedlings were grown in nutrient solutions with ammonium, nitrate or ammonium plus nitrate as nitrogen sources. The 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 glutamate dehydrogenase, in relation to the uptake of different nitrogen sources. The uptake studies revealed that western hemlock takes up ammonium faster than nitrate and that ammonium partially inhibits nitrate uptake. Efflux of H +, 1.26 μequiv H + μequiv ‑1 NH + 4, occurred to maintain charge balance in plants utilizing ammonium nitrogen whereas potassium served as a counterion in the uptake of nitrate. Nitrate reductase activity varied with nitrate availability in root tissue, but showed no response in needles. There was no glutamine synthetase response to differing nitrogen sources or uptake rates in root tissue, and little response in needles. Glutamate dehydrogenase activity in root tissue varied significantly with nitrogen source, being greatest in treatments containing ammonium. Results indicate that western hemlock may be adapted to sites where NH + 4 is the predominant N source.
- Publication:
-
Forest Ecology and Management
- Pub Date:
- January 1993
- DOI:
- 10.1016/0378-1127(93)90001-4
- Bibcode:
- 1993ForEM..59..179K