Sap Flow in Chamaecyparis obtusa in Relation to Water Economy of Woody Plants.

The rate of sap flow was measured by a heat pulse method. In order to determine the relationship between heat pulse velocity and actual rate of sap flow or transpiration, the water flow through the stem and heat pulse velocity were measured simultaneously on stem segments of young trees of Chamaecyparis obtusa (Fig. 1). A following linear equation between water flux (Wv, cc/cm2/hr) through the stem segments and heat pulse velocity (V, cm/hr) was established (Fig. 2): Wv=1.37V. Since the water flux in the equation is parallel to the sap flux in intact trees, the actual sap flux (Sv, cc/cm2/hr) is obtained from the following equation: Sv=1.37V. To obtain the actual amount of sap flow (SF, cc/hr), the cross sectional area of conducting system (A, cm2) is required beside the equation of the actual sap flux. The amount of sap flow is expressed in the following equation: SF=1.37AV