Abstract
The effect of rapid changes in the water potential of the root medium or the atmosphere was investigated with particular respect to water and ion uptake in young wheat plants. Either PEG 400 or PEG 6000 were added to the nutrient solution, so that the water potential was decreased from about 0 to –5 bars and –13 bars, respectively. Both water and ion uptake immediately decreased when the water potential of the medium was reduced. By raising the humidity around the shoots from 1400 N m−2 (60% RH) to about 2300 N m−2 (100% RH) water uptake decreased, whereas ion uptake transiently increased. If sodium chloride was added to reduce the water potential of the mutrient solution, ion uptake was found to decrease to essentially the same level as when PEG was used. It is suggested that a change in the water potential of the plants has effects on the active‐ion‐transport mechanism.