STUDIES ON WATER RELATIONS OF GRAPEVINE (VITIS VINIFERA)

On stressed and non-stressed 3-year-old grapevines grown in 100 1 containers leaf water potential (LWP) and diffusion resistance (LR) were measured during July and August 1978.\nIn non limiting soil water condition a linear correlation was found between LWP and the atmosphere water potential (AWP) at any time of the day, except at 10–11 am and 4–5 pm, when the plants were in a very unsteady status. At 7–8 am and 2–3 pm the regression lines were steeper than at the other times of the day. Explanations for that are given.\nIn non limiting water condition LWP was also related with transpirational fluxes (TF), decreasing linearly with increasing fluxes. The stressed plants did not show any of these relationships. The stressed grapevines usually showed lower LWP even at early morning hours. With relatively high AWP the stressed vines maintained sometime LWP similar to that of non stressed plants, doubling LR and reducing dramatically TF, limiting therefore the gas exchanges. After irrigation the stressed plants recovered fairly rapidly. In fact after 90 min LWP was similar to that of non-stressed plants but LR was much higher suggesting a slow metabolic recovering.\nIn July and August 1979 LWP and LR measurements were made on fruiting grapevines (FG) and on defruited plants (DG). FG showed a higher TF, because of a lower LR, but maintained LWP similar to that of DG, suggesting the importance of the fruit in the plant water balance either determining a more efficient water transport or acting as a capacitance.