Water relations of ‘Wijcik McIntosh’ apple trees

Abstract

SummaryAspects of water flow in columnar apple trees were analysed in relation to variation with height of leaf conductance to water vapour, tree morphology and vascular anatomy. Water potential gradients in transpiring trees were in the range of 0.02-0.09 MPa m1. Although the cross-sectional area of stem per unit leaf area supplied increased towards the tip of the tree, there was no evidence for a corresponding decline in water potential gradient, implying a decreased stem conductivity with height. Measurements of stem conductivity confirmed this, and the mean diameter of xylem vessels was also found to decrease with height. Mean leaf size, leaf area per unit length of stem, and specific leaf area were all smallest at the tops of the trees. Although leaf conductance tended to increase with height, it was most closely related to irradiance, not to leaf water status. The results indicate that columnar apple trees provide a useful model system for studying the limitations to water flow within fruit trees, ...