Calibration of sap flow estimated by the compensation heat pulse method in olive, plum and orange trees: relationships with xylem anatomy

Abstract

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.

Spatial variations in xylem sap flux density in evergreen oak trees with radial-porous wood: comparisons with anatomical observations

“…413 and 414), the sap flow at 40-60 mm was ignored. In addition, we assumed that spatial variation in F d at depths deeper than the outermost depth could be neglected for Q estimates (e.g., Lu et al 2000;James et al 2002;Fernández et al 2006). The theoretical water conductivity of a vessel (K n ; kg m MPa -1 s -1 ) was calculated according to Hagen-Poiseuille's law (see Tyree and Zimmermann 2002):…”

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…Yet their suitability for scheduling irrigation depends on the water stress indicator derived from the sap flow measurements. When the total plant sap flux is obtained with an invasive method (see the website mentioned above for differences between invasive and non-invasive sap flow methods), calibration of the raw data is required, for which correction factors must be previously derived for the species of interest [94,103,104]. In addition, a high number of sensors are usually required for trees with trunks of large diameter, because the azimuthal sap flow variability is usually high.…”

Regulated deficit irrigation in citrus: agronomic response and water stress indicators

“…The general underestimation in tree transpiration obtained in our study in all the cases could be in part consequence of using a low number of probes per tree but also because the "actual" unknown wound size might have been higher than the value used here (2.4 mm) which is the suggested value for citrus trees based on direct calibrations (Fernández et al, 2006).…”