Hydraulic conductivity and xylem structure in young kiwifruit vines

The aim of this study was to investigate in kiwifruit vines the hydraulic conductivity in relation to the morphology of the vascular system, i.e., the xylem structure. The study was carried out on one-year-old potted micropropagated Actinidia deliciosa ('Hayward') plants, grown under optimal water availability conditions. Flow through the stems sections was measured and the hydraulic conductivity values calculated. Anatomical investigations were also carried out on the same stem sections by using histochemical techniques and image analysis tools, in order to define structurally the stem conductive system in terms of xylem area, vessel size and density. The hydraulic conductivity values were consequently expressed as xylem hydraulic conductivity and vessel lumen hydraulic conductivity. In young kiwifruit stems, the vessel conductive area represented 18% of the total xylem area. The mean values of the calculated hydraulic conductivity (4.7 x 10(-9) m(4)s(-1)MPa(-1)) proved to be higher in comparison to other plant species. The conductivity measurements proved that kiwifruit have an efficient conductive system which enables the transport under optimal water availability of high amounts of water towards the leaves, therefore reducing daily variations in the leaf water potential.