Stomatal behaviour and water use efficiency in two cultivars of Olea europaea L.

A number of dry-down/recovery cycles were performed in three different experiments to determine changes in stomatal conductance in fully-expanded leaves of olive (cultivars 'Frantoio' and 'Leccino') plants grown in containers, with different watering regimes or by withholding irrigation. The level of water deficit was assessed by measurements of pre-dawn leaf water potential, whereas gas exchange parameters were measured by infrared gas analysis. Stomatal aperture and density were determined on frozen-hydrated leaves by low-temperature scanning electron microscopy. The cultivar 'Leccino' showed significantly higher water use efficiency than the cultivar 'Frantoio'; the latter cultivar had higher leaf conductance under well-watered conditions. In plants subjected to water deficit (pre-dawn leaf water potential less than -1.5 MPa) the differences in water use efficiency disappeared. Both cultivars recovered equally well upon relief of stress. Low-temperature scanning electron microscopy confirmed that stomatal aperture of 'Frantoio' was more than that of 'Leccino', while stomatal density and leaf area were similar in both cultivars.