© 2006 Heron Publishing—Victoria, Canada
Calibration of sap flow estimated by the compensation heat pulse method in olive, plum and orange trees: relationships with
xylem anatomy
J. E. Fernández (1, 3), P. J. Durán (1), M. J. Palomo (2), A. Diaz-Espejo (1), V. Chamorro (1) and I. F. Girón (1)
1. Instituto de Recursos Naturales y Agrobiología, Apartado 1052, 41080 Sevilla, Spain / 2. E.U.I.T.A., Departamento de Ciencias Agroforestales, Carretera de Utrera km 1, 41013 Sevilla, Spain / 3. Corresponding author (jefer@irnase.csic.es) / Received August 2, 2005; accepted September 27, 2005; published online March 1, 2006
Summary
The compensation heat pulse method is widely used to estimate sap flow in conducting organs of woody plants. Being an invasive
technique, calibration is crucial to derive correction factors for accurately estimating the sap flow value from the measured
heat pulse velocity. We compared the results of excision and perfusion calibration experiments made with mature olive (Olea europaea L. ‘Manzanilla de Sevilla’), plum (Prunus domestica L. ‘Songal’) and orange (Citrus sinensis (L.) Osbeck. ‘Cadenero’) trees. The calibration experiments were designed according to current knowledge on the application
of the technique and the analysis of measured heat pulse velocities. Data on xylem characteristics were obtained from the
experimental trees and related to the results of the calibration experiments. The most accurate sap flow values were obtained
by assuming a wound width of 2.0 mm for olive and 2.4 mm for plum and orange. Although the three possible methods of integrating
the sap velocity profiles produced similar results for all three species, the best results were obtained by calculating sap
flow as the weighted sum of the product of sap velocity and the associated sapwood area across the four sensors of the heat-pulse-velocity
probes. Anatomical observations showed that the xylem of the studied species can be considered thermally homogeneous. Vessel
lumen diameter in orange trees was about twice that in the olive and plum, but vessel density was less than half. Total vessel
lumen area per transverse section of xylem tissue was greater in plum than in the other species. These and other anatomical
and hydraulic differences may account for the different calibration results obtained for each species.
Keywords:
Mediterranean crop trees, transpiration, water consumption, wood characteristics.
