The prediction of grapevine transpiration by the Penman-Monteith (1973) model was tested by measurements of sap flow using the stem heat balance technique adapted to woody plants. Gauges clamped to the base of the stem, including heaters and sensors, were self-constructed by A. Peressotti and G. Delle Vedove, University of Udine (peressotti@palantir.dpvta.uniud.it) according to the indications of Steinberg et al. (1989). A CR10 (Campbell Scientific Corp., Logan Utah, USA) datalogger equipped with a AM416 relay multiplexer was programmed to record measurements every 15 s and to average and store them every 12 min. In order to calibrate sap flow sensors the sheath conductance of the gauge was daily recalculated using minimum pre-dawn values obtained after night calibration loops. A stem thermal conductance value of 0.54 W m-1 °C-1 was determined according to Sakuratani (1979). Leaf transpiration was also estimated by extrapolating single leaf gas exchange measurements to the whole canopy. To Penman-Monteith transpiration (ETE) calculate, air temperature and humidity, wind velocity (u), and solar radiation were recorded. Stomatal conductance of single leaves (rleaf), average leaf width (d) and horizontal (LAI) and vertical foliage density (p = the ratio between leaf area and the area of the vine canopy projected onto a vertical plane) were assessed. The canopy resistance (rc) of the vine was hourly calculated rc = rleaf / 0.5*LAI. The aerodynamic resistance (ra) was hourly calculated using an empirical relation: ra = 58p0.56 (d/u)0.5. The average LAI was 2.13 and the ratio (p) between the leaf area and the projection of leaves onto a vertical plane was 1.71. The transpiration data assessed with the three methods, i.e. Penman-Monteith, sap flow and single leaf transpiration, were in good agreement. There was a delayed response in the sapflow measurement relative to the estimate of transpiration rate based on leaf gas exchange readings. The delay may be attributed to the capacitance of the vine (Lovisolo et al. 1998). Consequently, as far as sapflow measurements are concerned, modifications in vine transpiration do not appear to be immediately reflected as a change in water flux through the trunk (Lascano et al. 1992).
Validation of the Penman-Monteith transpiration model by sap flow measurements in grapevines.
LOVISOLO, Claudio;FERRARIS, Stefano;SCHUBERT, Andrea
2000-01-01
Abstract
The prediction of grapevine transpiration by the Penman-Monteith (1973) model was tested by measurements of sap flow using the stem heat balance technique adapted to woody plants. Gauges clamped to the base of the stem, including heaters and sensors, were self-constructed by A. Peressotti and G. Delle Vedove, University of Udine (peressotti@palantir.dpvta.uniud.it) according to the indications of Steinberg et al. (1989). A CR10 (Campbell Scientific Corp., Logan Utah, USA) datalogger equipped with a AM416 relay multiplexer was programmed to record measurements every 15 s and to average and store them every 12 min. In order to calibrate sap flow sensors the sheath conductance of the gauge was daily recalculated using minimum pre-dawn values obtained after night calibration loops. A stem thermal conductance value of 0.54 W m-1 °C-1 was determined according to Sakuratani (1979). Leaf transpiration was also estimated by extrapolating single leaf gas exchange measurements to the whole canopy. To Penman-Monteith transpiration (ETE) calculate, air temperature and humidity, wind velocity (u), and solar radiation were recorded. Stomatal conductance of single leaves (rleaf), average leaf width (d) and horizontal (LAI) and vertical foliage density (p = the ratio between leaf area and the area of the vine canopy projected onto a vertical plane) were assessed. The canopy resistance (rc) of the vine was hourly calculated rc = rleaf / 0.5*LAI. The aerodynamic resistance (ra) was hourly calculated using an empirical relation: ra = 58p0.56 (d/u)0.5. The average LAI was 2.13 and the ratio (p) between the leaf area and the projection of leaves onto a vertical plane was 1.71. The transpiration data assessed with the three methods, i.e. Penman-Monteith, sap flow and single leaf transpiration, were in good agreement. There was a delayed response in the sapflow measurement relative to the estimate of transpiration rate based on leaf gas exchange readings. The delay may be attributed to the capacitance of the vine (Lovisolo et al. 1998). Consequently, as far as sapflow measurements are concerned, modifications in vine transpiration do not appear to be immediately reflected as a change in water flux through the trunk (Lascano et al. 1992).
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