The Theory and Practice of Measuring Transport Coefficients and Sap Flow in the Xylem of Red Maple Stems (Acer rubrum)

In this paper we report measurements concerning the conductivity of water and ions and the interaction between the two in excised pieces of xylem of red maple stems under various conditions. We have also demonstrated that it is possible to detect the flow of solutions through the stems of maple by measuring the degree of interaction between the flow of water and ions. In this technique we apply voltage pulses of ± V volts across a length of stem and detect the unequal current pulses resulting from the greater frictional drag when current (which is carried primarily by cations) is flowing against the water stream than when flowing with the water stream. The hydraulic conductivity of recent maple sapwood ranges from 30 to 90 cm3 sr1 cm-2 (J cm3)1 cm; in 2 ml KCl the electrical conductivity is roughly 3 x 104 mho cm-1 and the electro-kinetic cross coefficient is roughly 4x 10~5 A cm-2 (J cm3)1 cm.