Nitrogen saturation in northern hardwood forests and the N metabolism of Acer saccharum
- Univ. of Michigan, Ann Arbor, MI (United States)
- Michigan Technological Univ., Houghton, MI (United States)
It is generally assumed that plant assimilation constitutes the major sink for anthropogenic NO{sub 3}- deposition in temperate forests because growth is generally limited by N availability . However, few studies have directly determined the ability of overstory trees to take up and assimilate NO{sub 3}-. We studied the NO{sub 3}- nutrition of Acer saccharum Marsh. in four northern hardwood forests receiving experimental NO{sub 3}- additions equivalent to 30 kg N ha{sup -1} y{sup -1}. Kinetic parameters for uptake of NO{sub 3}- and NH{sub 4}+ by excised fine roots were determined using {sup 15}N, and rates of nitrate reductase activity (NRA) in leaves and fine roots were measured using an in vivo assay. Rates of leaf (7.87 nmol g{sup -1} h{sup -1}) and fine root (2.72 nmol g{sup -1} h{sup -1}) NRA were substantially lower than rates for most woody plants, and showed no response to NO{sub 3}- fertilization. The mean V{sub max} for NO{sub 3}- uptake in fine roots (0.67 {mu}mol g{sup -1} h{sup -1}) was approximately 30-times lower than the V{sub max} for NH{sub 4}+ uptake. At the present concentrations of NO{sub 3}- in soil solution, NO{sub 3}- uptake by fine roots already occurs at its maximum velocity, suggesting that Acer saccharum has a limited ability to directly assimilate NO{sub 3} entering these ecosystems from the atmosphere.
- OSTI ID:
- 95875
- Report Number(s):
- CONF-9507129-; ISSN 0012-9623; TRN: 95:004728-0143
- Journal Information:
- Bulletin of the Ecological Society of America, Vol. 76, Issue 2; Conference: 80. anniversary of the transdisciplinary nature of ecology, Snowbird, UT (United States), 30 Jul - 3 Aug 1995; Other Information: PBD: Jun 1995
- Country of Publication:
- United States
- Language:
- English
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