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Ben-Gurion University of the Negev (2013)

Water Relations in Date Palm Trees – a Combined Approach using Water, Plant, and Atmospheric Data

Sperling Or

Titre : Water Relations in Date Palm Trees – a Combined Approach using Water, Plant, and Atmospheric Data

Auteur : Sperling Or

Université de soutenance : Ben-Gurion University of the Negev

Grade : DOCTOR OF PHILOSOPHY (PhD) 2013

Résumé partiel
The date palm (Phoenix dactylifera L., cv. Medjool) is a widely cultivated crop, with high economic importance in arid Mediterranean regions, since this tree is well adapted to extreme environmental conditions. Nevertheless, for producing commercial fruit yields, date plantations require large amounts of irrigation water. As water is scarce in these regions, the share of low-quality (e.g of high salinity) water is large in date palm irrigation practices, leading in many cases to reduced growth and yields. Moreover, application of low-quality water entails a range of economic and environmental concerns, best addressed by high efficiency irrigation. Thus, irrigation of date palms should follow their actual water demands and allow sufficient leaching fraction in order to avoid salinization of the root zone. The monocotyledonous date palm lacks vascular cambium or renewal of xylem vessels and therefore cavitation of xylem vessels can cause significant reduction of water conductance. Under modern cultivation practices, the date palm root zone is continuously wetted. However, during summer midday, due to hydraulic constraints of soil and roots, transpiration could suppress the rate of water extraction from soil. In these times of extreme water demands additional intra-plant water exploitation strategies are essential for maintaining vital physiological activity. The aim of this dissertation is to present a thorough and comprehensive description of the soilplant-atmosphere water continuum in date palms, and the effects of high salinity irrigation on plant physiological performances and water budget. This work is based on the running hypothesis that the tolerance of date palms to high salinity irrigation-water entails inevitable losses in yields, inhibited growth, regulated water loss, and activation of protection strategies from photo and solute damage. Thus, a thorough investigation of the water continuum in date palms, comprising irrigation salinity, would exhibit the main physiological stresses date palms are exposed to under modern cultivation, and possibly lead to significant water saving. The common and practical Penman-Monteith equation was applied for determination of water use requirements ; this is an indirect-environmental approach integrating physiological and meteorological parameters. This method requires data accessible by common farmers but relies on empirical factors and therefore not applicable without extensive research. Also, data from direct water-balance measurements attained using weighing lysimeters, widely used in agricultural research, were collected and analyzed. Internal sensors for continuous water status and flow measurements, i.e., stem water content and sap flow sensors were constructed for the first time as part of this research. These sensors indicate water stress, define intra-flows, and possibly improve irrigation scheduling. Moreover, the sensors are inexpensive, easy to install, and require low maintenance while supplying all the relevant information for defining plant water status. Finally, date palms were treated with four irrigation salinities, 1.8, 4, 8, and 10 dS m-1, and solute allocation in the date palm and its relation to irrigation salinity was defined. Tissue samples were analyzed for their mineral concentration, resulting in a complete description of solute transport in the date palm

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