Contribution to transpiration of different tissues of kiwifruit vines from their water reserves

The trial was carried out in Metaponto (N 40° 24', E 16° 48') on fully-cropping kiwifruit vines propagated from cuttings. A number of plants were subjected to a period of stress by suspending irrigation. One month after the beginning of the trial the vines of the stressed treatments had reached pre-dawn leaf water potentials of -0.90 MPa and -0.60 MPa against -0.25 MPa in controls. At 14:00 hours potentials were -1.6 MPa in the vines having least water available, -1.4 MPa in those with an intermediate water availability and -0.9 MPa in controls. Transpiration at midday was 1 mmol H2O m-2 s-1 in the first group, 2 mmol H2O m-2 s-1 in the second and 4 mmol H2O m-2 s-1 in controls. Low transpiration levels in the stressed plants provoked a 6–8°C higher leaf temperature compared to controls. Water potential and transpiration fluctuations from pre-dawn to 14:00 hours determined a limited fluctuation in water content of exposed and shaded leaves in controls and in stressed vines. Fruits showed no change in their water content in the same period of time. Shoots, branches and roots gave up from 2 to 4% of their water content. In absolute terms, from pre-dawn to 14:00 hours the various organs of control vines, those with intermediate water availability ad those with least water available contributed to transpiration respectively 2.21 m3/ha, 1.35 m3/ha and 0.42 m3/ha of water. These values correspond respectively to 8.5%, 9.6% and 5.1% of the water lost through transpiration over the same period