Nutrient Uptake and Distribution in Subterranean Clover During Recovery from Nutritional Stresses I. Experiments with Phosphorus

Abstract

Young subterranean clover plants (Trifolium sub-terraneum L. cv. ''Mt. Barker''), raised at three phosphorus levels in culture solutions, were transferred to complete solutions and to solutions without phosphorus and grown for a further 7 days. After transfer to complete solutions, the roots retained approximately the same proportion of absorbed phosphorus at all pretreatment levels. In previously deficient plants most of the phosphorus translocated to the shoots was distributed to leaves existing at transfer, while in non-deficient plants most was distributed to leaves formed after transfer. In a similar experiment with 32P, phosphorus translocated to existing shoots during the first few days of recovery was less readily available the greater the previous phosphorus stress. By contrast, phosphorus accumulated in the roots was more available for subsequent translocation to new shoots the greater the previous stress. After transfer of plants in the first experiment to solutions without phosphorus, not net losses of root phosphorus were found for any of the pretreatments. Phosphorus in new leaves and petioles formed after the transfer had all been derived from existing shoots. Export from these shoots was relatively greater the higher the phos phorus status of the plant at transfer.