Effects of water stress on water relations, gas exchange and leap structure of olive tree

Olive (Olea europea L., cv 'Koroneiki') plants grown in 50-1 containers filled with a sandy-clay-learn soil, were subjected to two irrigation regimes during the dry season (April to October) for two years to evaluate the physiological responses and anatomical changes induced by water stress. Irrigation was applied when the soil water potential reached -0.03 MPa and -1.5 MPa for the wet and dry treatments, respectively. In stressed plants predawn leaf water potential (Psi) declined by 4.8 MPa after 8 days of withholding water, whereas the turgor potential (PsiP) remained positive due to a rapid decrease in osmotic potential, indicating their ability for osmoregulation. Mainly mannitol and in less extent glucose seem to contribute to the osmotic adjustment. Bulk modulus of elasticity (epsilon) was significantly higher in stressed compared to well irrigated plants. photosynthetic rate (Pn) as well as stomatal conductance (g(delta)) were decreased in stressed plants when Psi fall below -1.3 MPa. After re-watering, Pn and gs reached the 80% of the values attained by the well-watered plants. The volume fraction of intercellular spaces of the upper palisade parenchyma, the spongy parenchyma as well as the lower palisade parenchyma were slightly but significantly lower in stressed plants, while the density of mesophyll cells increased compared to the well-watered plants.