ISHS Acta Horticulturae 526: V International Symposium on Grapevine Physiology
COMPARISON OF HEAT BALANCE AND GAS EXCHANGE METHODS TO MEASURE TRANSPIRATION IN IRRIGATED AND WATER STRESSED GRAPEVINES |
| Authors: | L. Escalona, J. Flexas, H. Medrano |
| Keywords: | Vitis vinifera, Drought, Sap Flow, Photosynthesis |
| Abstract:
Heat balance and leaf gas exchange methods were compared to measure plant transpiration rate in grapevine potted plants in different environmental conditions. Diurnal time courses of last fully expanded leaf gas exchange rates, and sap flow rates were compared in sunny and cloudy days, in well watered and water-stressed plants. Total plant transpiration rates were derived from instantaneous leaf gas exchange and plant leaf area measurements. In sunny and cloudy situations, different transpiration rates were observed. Rate of transpiration showed to be completely dependent of the irradiance. Any change in the amount of irradiance causes an immediate response in transpiration rate, measured in the whole plant with heat balance method. Similar response was observed also in an individual leaf, measured with gas exchange method. The sap flow measurements carried out by heat balance method and the plant transpiration rates derived from leaf gas exchange rates showed quite high correlation in irrigated plants (r2=0,96). When plants were under water stress (  pd= -0,58 MPa), this correlation didn't stabilize, even total daily rates of plant transpiration and sap flow were quite similar.
These results shows the high interest of sap flow measurements for ecophysiological field studies, showing that in high transpiratory flux conditions it is possible to estimate transpiration rate variations continuously from the sap flow measurements obtained with the heat balance method. However, for permanent lower transpiratory fluxes., as recorded for water stressed plants, the sap flow measurements can only reflect, with certain accuracy, the total daily transpiration rate, but not the variations along the day. | |
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