Study on root absorption responding to environmental stress by using hydroponic systems

This study deals with effects of high temperature stress and salt stress on root physiological functions by using the system newly developed for measurements of water and nutrients uptake by roots. Dynamic and simultaneous evaluation of rates of water and nutrients uptake by roots was enabled in the hydroponic system. Rates of water and nutrients uptake by roots were evaluated simultaneously on the basis of time courses analyses of water balance and nutrients balance in the system. Furthermore, the simultaneous evaluation of water and nutrients uptake rates enabled estimation of concentration of each nutrient in xylem sap. In the short-term (one or two weeks), the high root temperature activated water and nutrients uptake through decrease in water viscosity, and the salt stress significantly depressed water uptake rate through decrease in osmotic potential of the nutrient solution, which retarded mass flow in the nutrients uptake. On the other hand, the long-term (several weeks) of the high root temperature depressed water and nutrients uptake and resulted in growth depression and browning in roots. The long-term effects of the high root temperature were considered to relate to the reduced oxygen solubility and the increased enzymatic oxidization of phenolic compounds in root epidermal and cortex tissues. Thus, the short-term effects of the high root temperature and the salt stress were brought mainly through the physical processes, and the long-term effects of the high root temperature were brought through the physiological processes.