ROOT-GROWTH, OSMOTIC ADJUSTMENT AND NO3- UPTAKE DURING AND AFTER A PERIOD OF DROUGHT IN ARTEMISIA-TRIDENTATA

Nitrate uptake in pot-grown, well watered and water-stressed Artemisia tridentata seedlings was determined both during drought and during recovery from drought using (NO3-)-N-15. Water deficit caused a 40% decrease in NO3- uptake compared to well watered plants and the restricted NO3- uptake persisted 4 days after rewatering. Between 4 and 14 days after rewatering, NO3- uptake in previously stressed plants was the same as that of the controls. Root relative growth rate (RGR) during the drying cycle was about one-fourth that of the control, but recovered to the control level within 4 days after rewatering. Between 4 and 14 days after rewatering, the previously droughted plant roots exhibited nearly three times greater RGR than the control plant roots. Estimates of root solute content indicated that at no time during the stress and recovery periods did the droughted roots exhibit osmotic adjustment. Changes in root growth properties were uncoupled from turgor. During the recovery period, drought-induced adjustments in cell wall yielding properties are thought to have increased root growth in previously stressed seedlings. Nevertheless, the greater root growth of previously droughted plants did not result in more NO3- acquisition than in control plants. The pattern of NO3- uptake upon rewatering was apparently more closely associated with root uptake capacity.