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Abstract
Three varieties of olive, Barnea, Arbequina and Proline, varying in salt tolerance, were examined to check the sensitivity of their root system hydraulic properties to salinity. Up to three levels of saline water (EC = 1.2, 4.2 and 7.5 dS m−1) were used for long-term irrigation of mature trees. Specific conductivities and embolism rates of roots and branches were estimated by low-pressure conductivity measurement; variability and plasticity of root and branch axial conductivities were calculated. Cross-sections of roots were analysed with respect to xylem anatomy. Barnea, and to a minor degree Arbequina, were found to be more salt-resistant than Proline. Axial root hydraulics under salt stress reacted in a more plastic fashion than branch conductivities. Increased specific conductivities of roots, different plasticities of root hydraulics and modifications in mean conduit diameters can be dismissed as foremost reasons of the observed differences in salt resistance. Instead, a high within-population variability in root conductivity, as found in the salt-tolerant Barnea and Arbequina varieties, coming to full effect in high conductivity roots of Barnea trees, and an increased bimodal distribution of conduit sizes may represent favourable traits to enhance water uptake in soils with heterogeneous salinity.
Acknowledgements
The authors thank Prof. Y. Waisel for his critical comments on an early version of the manuscript, and Prof. M. Silberbush and S. Weissbein for fruitful discussion and excellent support in the field. The first author was financially supported by the Dryland Research Specific Support Action (DR-SSA) of the European Union (FP6). This project was developed within the COST E38 action “Woody Root Processes”.
