Kinetics of root ion absorption affected by environmental factors and transpiration I. Measurement system for intact roots

For sustainable production of high-quality plants, information about kinetics of root absorptive functions responding to change in environmental condition is essential. A system for measuring rates of water absorption, ion absorption and respiration in intact roots was developed, and the system performance was found to be reliable with a relative error less than 3.5% and applicable under different root zone temperatures and dissolved O₂ concentrations. Furthermore, the simultaneous measurements of rates of water and ion absorption enabled the evaluation of ion concentration in the xylem sap. The root absorptive functions were enhanced with increase in root zone temperature, and root respiration was depressed by the low dissolved O ₂ under the high root zone temperature of 35°C. In addition, the absorbed water diluted the xylem sap, and this dilution effect on the concentration of each ion in the xylem sap appeared in different patterns. These results suggest that the system developed is applicable for the analyses of the absorptive functions of intact roots responding to change in environmental condition.