DIURNAL CHANGES IN GAS EXCHANGE AND WATER RELATIONS IN FIELD GROWN GRAPE VINES

Diurnal changes in gas exchange and stomatal conductance in relation to leaf water (w), osmotic (s), turgor potential (p) and relative water content (R.W.C) were studied in leaves in field grown grape vines (V. vinifera L. cv Roditis). The vines were cordon trained -a training system used widely in Greece-and the orientation of the rows was north-south. The measurments were made on fully expanded exterior leaves, on the eastern and western side of the canopy. s of leaves of both sides decreased during the day and helped maintain a positive p. The reduction in s was largely due to active solute accumulation in leaf cells. Photosynthetic rate was higher on the eastern side and declined in leaves of both sides when leaf water potential fell below - 1.1 MPa. Transpiration rate which was also higher on the eastern side, reached a maximum at midday and then decreased. The onset of decline occured at a lower leaf water potential (-1.3 MPa) than photosynthesis. The calculated water use efficiency (W.U.E.) indicated that the leaves of the eastern side of the canopy were more efficient.