Drought stress-induced variation of pressure-volume relationships in Olea europaea L cv "Coratina"

The aim of this study was to determine the effects of water stress on total water potential components, tissue water content, maximum elastic modulus and osmoregulation capacity evaluated by means of the pressure-volume curves technique. The trial was conducted using two year-old ownrooted olive trees, cv. "Coratina", grown in 18 l containers and subjected to different stress levels determined on the basis of predawn leaf water potential measurements. Osmotic potentials at saturation (pi(100)) were -2.06 MPa in controls and -2.81 MPa in the most stressed treatment. Osmotic adjustment determined a broadening of the range within which turgor potentials remained positive. At incipient plasmolysis, osmotic potential (pi(0)) in fact varied from -3.07 in controls to -3.85 MPa in the most stressed plants, and relative water content (RWC0) from 77.8% to 74.5%. The maximum elastic modulus calculated at full turgor was 11.6 MPa in the leaves of controls and of the first stress level (-1.6 MPa) and 15.1 and 18.6 MPa in the second (-3.3 MPa) and third (-5.2) stress levels respectively. High osmotic adjustment values and the rigidity of the cell wall induced high potential gradients between leaves and roots, making for water absorption through roots even at low soil water potentials.