Leaf water status and gas exchange of field-grown olive trees of the cultivars

Leaf water status and gas exchange were investigated in trees of two olive cultivars, Ascolana Tenera and Kalamata, to estimate the sensitivity to water stress. Three different irrigation regimes were applied: T33 and T66 received 33 and 66% of crop evapotranspiration, respectively, whereas T0 was the rain-fed control. Prolonged Summer drought strongly reduced the soil water content [Theta sub(v)] in the T0 treatment of both cultivars, as compared to T33 and T66. Ascolana Tenera showed a better water status than Kalamata in both dry and wet soil conditions. The minimum leaf water potential [psi sub(l)] observed at the end of July in the rainfed treatment was -3.81 MPa in Kalamata and significantly higher in Ascolana Tenera (-3.25 MPa) when soil water content [Theta sub(v) = 20%] was at wilting point. Moreover, the pre-dawn psi sub(l) in T66 measured in late Summer was -0.71 MPa in Ascolana Tenera and -1.31 MPa in Kalamata, indicating a greater degree of water stress in the latter cultivar. Optimal soil moisture in early Summer allowed relatively high gas exchange with overall mean values of 0.140 mol mE-2 sE-1 for stomatal conductance [g sub(s)] and 12 micronmol mE-2 sE-1 for leaf photosynthesis (A). During late Summer, the stomata in T0 almost closed in both cultivars and Kalamata presented a lower minimum g sub(s) (0.017 mol mE-2 sE-l) compared to Ascolana (0.030 mol mE-2 sE-1), meanwhile A was reduced to 11.2% in Kalamata and 27% in Ascolana Tenera as compared to T66. A was more affected by psi sub(l) in Kalamata than in Ascolana Tenera