Transpiration and root water uptake by olive trees

While the cultivated olive tree (Olea europaea L.) is known to be sclerophyllous and effective at tolerating drought, little is known of its short-term water-use dynamics for most studies have been based on longer- term, water-balance in formation. We present here, for the first time, heat- pulse measurements of the sap flux measured not only within the semi-trunk of an olive tree, but also within a root excavated close to the stump. One tree in the olive grove near Seville in Spain had regularly received basin irrigation during the summer, whereas the other, growing on this deep silt loam, had been without water for over 3 months. Following a flood irrigation of 730 L to a dyked area around the tree, the regularly-irrigated olive maintained a transpiration rate of 1.65 mm3 mm-2 d-1 on a leaf area basis, for only 3 days following the irrigation. This rate was maintained for a total consumption of 110 L. It then begun again to limit its rate of water use with transpiration falling below that predicted for well-watered conditions by the Penman-Monteith equation. The flow of sap in the near- surface root dropped concomitantly. Meanwhile the unirrigated tree was using water at just 0.78 mm d-1. Yet following an irrigation of 870 L it only lifted its consumption to 1.12 mm d-1, on a leaf area basis. Neither did it recover its leaf water potential following this wetting because of an inability to refill cavitated vessels. These data again show olive to be a parsimonious and cautious consumer of soil water.Consejo Superior de Investigaciones Científicas.Peer Reviewe