The Uptake and Distribution of Copper in Some Forage Grasses as Affected by Nitrate-nitrogen Supply in Flowing Solution Culture

The effect of changes in nitrate-nitrogen supply on the absorption and distribution of copper was examined in grasses grown in flowing solution culture with a maintained concentration of copper. Absorption by roots (μg Cu g−1 dry root) decreased markedly when nitrogen had been depleted or was maintained at 0.1 mg l−1 N, but there was an immediate increase when nitrogen was maintained at 1.0 or 10.0 mg l−1. There were also large increases in the concentration of copper in the shoots of plants grown with 1.0 and 10.0 mg 1−1 N. The roots of plants grown with 0.1 or 1.0 mg 1−1 N retained similar proportions of uptake, but a lower proportion was retained when the plants were grown with 10.0 mg 1−1. Although a lower proportion of the copper was associated with cell walls in the plants grown at 10.0 mg 1−1 N this was the result of a lower content of cell walls rather than an effect on copper itself. In a longer-term experiment in conventional solution culture with a range of nitrogen concentration, the concentration of copper in shoots was largely determined by shoot growth.