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Chronic Atmospheric NO⁻ Deposition Does Not Induce NO⁻ Use by Acer saccharum Marsh
William C. Eddy, Donald R. Zak, William E. Holmes and Kurt S. Pregitzer
Vol. 11, No. 3 (Apr., 2008), pp. 469-477
Published by: Springer
Stable URL: http://www.jstor.org/stable/40296299
Page Count: 9
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The ability of an ecosystem to retain anthropogenic nitrogen (N) deposition is dependent upon plant and soil sinks for N, the strengths of which may be altered by chronic atmospheric N deposition. Sugar maple (Acer saccharum Marsh.), the dominant overstory tree in northern hardwood forests of the Lake States region, has a limited capacity to take up and assimilate NO₃⁻. However, it is uncertain whether long-term exposure to NO₃⁻ deposition might induce NO₃⁻ uptake by this ecologically important overstory tree. Here, we investigate whether 10 years of experimental NO₃⁻ deposition (30 kg N ha⁻¹ y⁻¹) could induce NO₃⁻ uptake and assimilation in overstory sugar maple (approximately 90 years old), which would enable this species to function as a direct sink for atmospheric NO₃⁻ deposition. Kinetic parameters for NH₄⁺4 + and NO₃⁻ uptake in fine roots, as well as leaf and root NO₃⁻ reductase activity, were measured under conditions of ambient and experimental NO₃⁻ deposition in four sugar maple-dominated stands spanning the geographic distribution of northern hardwood forests in the Upper Lake States. Chronic NO 3 ~ deposition did not alter the V max or K m for NO₃⁻and NH₄⁺ uptake nor did it influence ₃⁻ reductase activity in leaves and fine roots. Moreover, the mean V max for NH₄⁺ uptake (5.15 nmol ¹⁵N gɻ¹; hɻ¹;) was eight times greater than the Vmax for NO₃⁻ uptake (0.63 ¼mol ¹⁵N gɻ¹; hɻ¹;), indicating a much greater physiological capacity for NH₄⁺ uptake in this species. Additionally, NO₃⁻ reductase activity was lower than most values for woody plants previously reported in the literature, further indicating a low physiological potential for NO₃⁻ assimilation in sugar maple. Our results demonstrate that chronic NO₃⁻ deposition has not induced the physiological capacity for NO₃⁻ uptake and assimilation by sugar maple, making this dominant species an unlikely direct sink for anthropogenic NO₃⁻ deposition.
Ecosystems © 2008 Springer