Kinetics of Root Ion Absorption Affected by Environmental Factors and Transpiration II. Environmental Effects and a Concentration-Dependent Model

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Welsh onion plants (Allium fistulosum L.cv. Koutou) were grown under the different conditions of root zone temperature and dissolved O2 concentration. The absorptive functions in intact roots were analyzed by evaluating rates of water absorption, ion absorption, respiration and ion concentration in xylem sap simultaneously by applying the measurement system newly developed in the precedent study. The root water and ion absorption were activated with increase in root zone temperature, and the long term treatment with the high temperature and the low dissolved O2 concentration in the root zone significantly depressed water and ion absorption, while ion concentration in the xylem sap was not significantly affected by the root zone temperature. These suggest that the temperature dependence observed in root ion absorption is brought mainly through the temperature dependence of water absorption. A concentration-dependent model based on the theory of enzyme kinetics was applicable to kinetics of the root ion absorption responding to the root zone environment. The effects of root zone temperature and ion concentration on the root ion absorption were represented well by the concentration-dependent model which involves two parameters sensitive to changes in conditions of plants and the environment.