Cation uptake by Douglas-fir seedlings grown in solution culture

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Abstract
Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were grown in nutrient solutions and cation uptake was measured by disappearance from solution. Although seedlings were uniform in size and weight, a range of uptake rates was observed. Potassium and calcium uptake rates were determined over a range of cation concentrations. Using the Michaelis–Menten formula, kinetic constants were calculated for potassium (Km = 0.017 mM) and for calcium (Km = 0.043 mM). These values were similar to those reported for other plant species. Temperature optima were determined (20 °C for potassium and 26 °C for calcium), indicating that cation uptake was an active metabolic process, sensitive to temperature. Low levels of calcium were required for both potassium and magnesium uptake; at higher levels of calcium, magnesium uptake was reduced.