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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
Ecosystems
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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Chronic Atmospheric NO⁳⁻ Deposition Does Not Induce NO⁳⁻ Use by Acer saccharum Marsh
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Abstract

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.

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