Transpiration from a kiwifruit vine as estimated by the heat pulse technique and the Penman-Monteith equation

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Abstract
Heat pulse velocities were measured at 4 depths in the stem of a kiwifruit plant (Actinidia chinensis Planchon) throughout one lateautumn day, and sap velocities and total stem sap flux were calculated from physical principles without resorting to empirical calibration. Concurrent measurements of net radiation, air temperature, vapour pressure deficit, wind speed, and stomatal conductance were utilised in a second, independent calculation of transpiration based on the Penman-Monteith combination equation. Results indicated that most flow occurred in the outer ring or rings of the stem xylem tissue, and there was a close relationship between fluxes estimated by the 2 methods. We conclude that heat pulse velocity measurement is potentially a practicable method for measuring transpiration rates in kiwifruit.