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Loss of hydraulic functioning at leaf, stem and root level and its role in the stomatal behaviour during drought in olive trees

Torres-Ruiz, J.M., Díaz-Espejo, A., Perez-Martin, A., Hernandez-Santana, V.
Acta horticulturae 2013 no.991 pp. 333-339
drought, irrigation, leaf water potential, leaves, olives, plant available water, roots, stems, stomatal conductance, stomatal movement, trees, water stress, xylem
Knowing the mechanisms and factors related with the control of the stomatal behaviour by plants is crucial for understanding the variation of transpiration with time or among plants under different conditions. The loss of hydraulic functioning in some parts of the plants has been reported to have an important influence in the plant stomatal closure and, therefore, in the plant transpiration. Both low soil water availability and high atmospheric demand, common in Mediterranean regions, can cause plants to reach water stress levels limiting their hydraulic functioning due to cavitation of xylem conduits, among other factors. On this basis, our aims in this study were (i) to determine the loss of hydraulic functioning at different plant levels (leaves, stems and roots), and (ii) to evaluate the influence of the loss of hydraulic functioning at those levels on the stomatal behaviour of olive trees. Experiments were carried out in 1-year-old olive plants grown in pots in which irrigation was withheld for an increasing water stress. The irrigation was resumed and the end of the study for the plants to recover. The seasonal courses of the stomatal and hydraulic (in leaves, stems and roots) conductances were determined. Results showed a considerable decrease of the stomatal conductance in plants with leaf water potential lower than ca. -1.5 MPa. Marked losses of hydraulic functioning were also observed in leaves and roots at water potentials lower than ca. -1.5 MPa, but not in stems which showed a lower vulnerability to cavitation. Results showed a certain hydraulic segmentation that confines the loss of the hydraulic functioning in the leaves, and that leaves were the most vulnerable component of the hydraulic system, being well correlated with stomatal conductance during the dry-down period but not during recovery.