The relation between oxygen and water uptake by roots of intact plants

Vita.Bean plants (Phaseolus vulgaris L. var. 'Blue Lake') were grown in small pots, transferred to large root chambers with washed quartz sand and further established until the flowering stage, in a large growth chamber. Maximum irradiance at the level of the established plants averaged 74Wm⁻². Daylength was set for 14 hours with a simulated sunrise and sunset over 2-3 hours each. The plants were tested in a stem chamber attached to the root chamber so that the root and upper plant environments were separately controlled. A continuous flow system was used in both chambers. Oxygen uptake and water uptake measurements were made with a polarographic electrode and differential psychrometer respectively, under varying oxygen concentrations from 0.4-21% and standard transpiration conditions of about 44% relative humidity and average irradiance of 47Wm⁻². A potential of -0.5 bar was maintained on the root chamber. Leaf diffusion conductance was monitored with a diffusive resistance meter. The data showed a direct linear relation between oxygen uptake and water uptake in individual and combined data when expressed on a unit root weight and unit leaf area, respectively. Data was excluded when there was suspected damage to the root tips and where a sudden large increase in oxygen level was introduced after prolonged exposure to low oxygen levels. Bean roots exposed to 1.9 to 1.4% oxygen for longer than 8 but less than 18 hours showed a disruption in water uptake. This was observed as a temporary increase to the maximum water uptake for about 4 hours, followed by a decrease to about 5% of the maximum rate. The ratio of water uptake to oxygen uptake ranged from 179 to 322 on a weight basis. Recovery from long exposure to low oxygen levels was delayed for 1 day and 5 days was not long enough for recovery of the maximum water uptake rates observed before the low oxygen treatment