The Relationship Between Oxygen and Water Uptake by Roots of Intact Bean Plants

Abstract

To facilitate simultaneous measurements of root oxygen and water uptake, bean plants (Phaseolus vulgaris L. var. ‘Blue Lake’) were grown in washed sand in a root chamber which could be isolated from a chamber used to enclose the aerial portion of the plant. A continuous flow system was used in the root chamber and shoot chamber to measure oxygen consumption and transpiration, respectively. A good relationship between root oxygen uptake and transpiration was found during periods where the plants were subjected to gradual decreases in oxygen concentrations in the air in the root zone and during periods after some recovery had occurred as a result of reintroduction of 21% O2. The relationship failed, however, when plants were subjected to prolonged low oxygen concentrations, probably as a result of root injury, and when plants were abruptly given an ample supply of oxygen following a period of O2 deficiency, probably as a result of the need for oxygen to grow new roots before water uptake could begin again. For conditions other than those excluded, the correlation between root oxygen uptake and transpiration was 0.89. Transpiration decreased slightly as the oxygen concentration in the root zone decreased from 21 to 3%. Below 3%, the transpiration varied widely and depended on the length of time that the plant had been exposed to the decreased concentration. Recovery from damage resulting from low oxygen concentrations depended on the length of time the roots were subjected to the low concentrations. In some cases, full recovery was not achieved in 5 days. The ratio of the uptake of oxygen to water averaged 1:250 for the plants tested.