Influence of root zone oxygen stress on potassium and ammonium absorption by Myrobalan plum rootstock

Growth chamber experiments were conducted with 'French' prune (Prunus domestica L.) scions grafted on Myrobalan 29C (P. cerasifera Ehrh.) rootstocks grown in nutrient solution to characterize K and NH₄ uptake before, during, and after anaerobiosis. Conditions of oxygen stress were imposed by removing the source of aeration and bubbling solutions with nitrogen gas. At solution oxygen concentrations less than 1%, K leaked from plant roots. After 18 h of anaerobic conditions, aeration was restored and K depletion from solution occurred within 2 h. Uptake of K the following day was similar to that before oxygen stress was imposed. Under similar conditions with solution oxygen concentrations less than 1%, both K and NH₄ uptake were inhibited. Potassium leakage from roots was significantly greater than that of NH₄. The presence of NH₄ had no significant effect on K leakage from roots. Signs of wilting during oxygen stress appeared first on those trees that received NH₄. Potassium uptake by rootstocks in the presence of NH₄ was inhibited prior to and following anaerobiosis. However, the extent of NH₄-induced inhibition of K uptake before anaerobiosis was similar to the K uptake inhibition after anaerobiosis.