LEAF WATER POTENTIAL AS A PARAMETER IN DEFINING PLANT WATER STATUS AND AVAILABLE SOIL WATER.

For all species, leaf water potential measured before sunrise represents a useful parameter in defining plant water status and soil water available, while there is no correlation between these parameters recorded during the day for peach and kiwi plants.

Species react in different ways to the soil water content. Olive trees transpire less than peach when soil water content is high, while at low levels of A.W. water consumption in olive trees is higher than in peach trees. Kiwi plants are the most sensitive to decreases in soil water available.

In the case of peach trees, when soil water content was approximately 30% of A.W. the fruit growth rate diminished. Pre-dawn leaf water potential at the same level of A.W. ranged from -0.6 to -0.8 MPa. The effect of water stress on fruit growth was more marked during the phase of rapid swelling of the fruit due to cell expansion.

The critical level of A.W. for kiwi trees seems to be around 40–50% of A.W., since at that level transpiration during the hot hours of the day decreases and leaf damage due to the high temperatures can be seen.

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