Sap flow as an indicator of transpiration and the water status of young apricot trees

The relationship between water loss via transpiration and stem sap flow in young apricot trees was studied under different environmental conditions an d different levels of soil water status. The experiment was carried out in a greenhouse over a 2-week period (November 2-14, 1997) using three-year-ol d apricot trees (Prunus armeniaca cv. Bulida) growing in pots. Diurnal cour ses of leaf water potential, leaf conductance and leaf turgor potential als o were recorded throughout the experiment. Data from four days of different enviromental conditions and soil water availability have been selected for analysis. On each of the selected days the leaf water potential and the me an transpiration rates were well correlated. The slope of the linear regres sion of this correlation, taken to indicate the total hydraulic resistance of the tree, confirmed an increasing hydraulic resistance under drought con ditions. When the trees were not drought stressed the diurnal courses of sa p flow and transpiration were very similar. However, when the trees were dr oughted, measured of sap flow slightly underestimated actual transpiration. Our heat-pulse measurements suggest the amount of readily available water stored in the stem and leaf tissues of young apricot trees is sufficient to sustain the peak transpiration rates for about 1 hour.