Water Use of Kiwifruit Vines and Apple Trees by the Heat-Pulse Technique

Abstract

Green, S. R. and Clothier, B. E. 1988. Water use of kiwifruit vines and apple trees by the heat-pulse technique.–J. exp. Bot. 39: 115–123. The compensation heat-pulse method has been used to measure sap velocities in the stem of kiwifruit vines (Actinidia deliciosa) and apple trees (Malus sylvestris × Red Delicious). Because of the high flow rates typical in kiwifruit vines, we were unable to measure heat-pulse velocity using standard probe spacings. We increased the spacing between sensors with the downstream sensor 20 mm and the upstream sensor 5-0 mm respectively from the heater probe. Corrections for flow blockage by the probes were re-calculated at this new spacing for our 2-0 mm-diameter heater and teflon temperature probes following the procedure of Swanson and Whitfield (1981) Sap flux through the stem was found from heat-pulse velocities at four radial depths in the stem. Fluxes measured using the heat-pulse technique were compared with water uptake from apple trees and kiwifruit vines that had been cut-off at the base and the butt placed in a container of water. Heat-pulse measurements were also compared with known flow rates through stem-sections of kiwifruit vine in the laboratory. In apple the heat-pulse measurements agreed with independent flux measurements in excision experiments. In kiwifruit the independently measured fluxes were consistently 1.6 times larger than the fluxes measured with the heat-pulse method. Possible reasons for this anomalous result in kiwifruit vines are discussed