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+ 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 NO3- deposition did not alter the V max or K m for NO3- and NH4+ uptake nor did it influence NO3- reductase activity in leaves and fine roots. Moreover, the mean V max for NH4+ uptake (5.15 μmol 15N g-1 h-1) was eight times greater than the V max for NO3- uptake (0.63 μmol 15N g-1 h-1), 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.