ROOT TEMPERATURE EFFECT ON HYDRAULIC CHARACTERISTICS OF ROOTS IN HYDROPONICS

Abstract

Water uptake and gas exchange in cucumber roots (Cucumis sativus L. cv Chojitsu-Ochiai) were examined in a root temperature control system of air-tightened hydroponics. The effect of root temperature on water uptake rate was found in a sigmoidal pattern: The water uptake rate was reduced at root temperatures lower than 12°C. The responses of O2 decrease rate and CO2 increase rate to the root temperatures appeared almost parallel to the pattern of water uptake rate. Furthermore, the effect of root temperature on total root resistance was examined in a detached root system by applying suction to the proximal end. The total root resistance became higher at lower root temperatures. Thus, it could be suggested that at the lower root temperatures, the increase in root hydraulic resistance in relation to the inhibited root respiration results in the decrease in water uptake in intact plants. On the other hand, the total root resistance at lower root temperatures in figleaf gourd plant (Cucurbita ficifolia B.) which is more tolerant of low temperature were kept higher as compared with that of cucumber plant. This fact indicates that low temperature tolerance in plant growth closely relates to root hydraulic characteristics at the lower root temperatures.