Water uptake and growth of cucumber plants (Cucumis sativus L.) under control of dissolved O₂ concentration in hydroponics

Dissolved O₂ concentration ([O₂]) in nutrient solution was controlled at 0.01, 0.10 and 0.20 mM with accuracy of ±0.005 mM in a newly developed hydroponic system, and the effects of [O₂] on water uptake and growth of cucumber plants (Cucumis sativus L.) were analyzed. For evaluating water uptake rate under the control of [O₂] water flux at the stem base was measured on-line with ±5% in accuracy, 1 mg s^-1 in resolution and 1 min in time constant by heat flux control (HFC) method. Water uptake rate was drastically increased by lighting to the plant at each [O₂] and water uptake per day was depressed in proportion to decrease in [O₂]. In the plants grown for 10 days, leaf area, fresh weight and dry weight of leaves decreased at lower [O₂], while stem length and number of leaves were scarcely affected. These facts suggest that membrane permeability of root cells reduces at lower [O ₂] through respiration-dependent processes, and growth is inhibited through leaf turgor loss caused by the depressed water uptake of roots in O ₂-deficient nutrient solution in hydroponics.