Short communication Calcium increases sodium exclusion in olive plants J.C. Melgar * , M. Benlloch, R. Ferna ´ndez-Escobar Departamento de Agronomı ´a, Universidad de Co ´rdoba. Edificio ‘Celestino Mutis’, Campus Universitario de Rabanales, Ctra. Madrid-Ca ´diz km. 396, Co ´rdoba 14071, Spain Received 18 April 2005; received in revised form 18 January 2006; accepted 7 April 2006 Abstract ‘Picual’ olive cuttings were grown in a greenhouse under saline conditions in 2 L plastic pots containing perlite. Plants were irrigated with a nutrient solution plus 75 mM NaCl and 0, 2.5, 10 or 40 mM CaCl 2 . Vegetative growth, leaf and root Na + and Ca 2+ concentrations were measured. Na + toxicity symptoms were observed in plants non-treated with Ca 2+ . Shoot length was higher in Ca 2+ treated plants, although shoot growth was reduced at 40 mM CaCl 2 , probably due to the high total ion concentration reached in the external solution. Ca 2+ supply linearly increased leaf and root Ca 2+ concentration and decreased leaf Na + concentration. However, there were no differences in root Na + concentration. Results indicate Ca 2+ may take part in the Na + exclusion mechanism, mainly preventing Na + transport to the shoot, that may be an important ability for survival under saline conditions. # 2006 Elsevier B.V. All rights reserved. Keywords: Olea europaea; NaCl; Sodium exclusion; Calcium 1. Introduction Ca 2+ supply to the saline soil solution regulates Na + uptake by plants and can prevent the accumulation of toxic levels of Na + (Maas, 1993). However, effectiveness in alleviating the toxic effect of Na + depends on the Ca 2+ and Na + concentration and on the species (Grattan and Grieve, 1999). Olive trees cultivation in saline soils depends on the cultivar (Marı ´n et al., 1995). Its tolerance is mainly associated to ion exclusion mechanisms located in the root (Benlloch et al., 1991; Tattini et al., 1995) and consisting in holding Na + and Cl  at the root level and limiting the accumulation of these ions in the shoot. Cl  uptake and transport to the shoot in olive trees is lower than for Na + (Tattini et al., 1992), without causing negative effects if concentrations do not exceed 80 mM Cl  in tissue water (Bongi and Loreto, 1989). Although the mitigating effect of Ca 2+ on the adverse NaCl effects has been reported in many plant species (La Haye and Epstein, 1969), the role of Ca 2+ has not been sufficiently studied in some perennial trees such as the olive tree. Considering that olive trees are mainly grown in areas with high salinity, the objective of the present study was to determine the effect of supplementary Ca 2+ on Na + uptake and transportation in olive plants grown under saline conditions. 2. Materials and methods Mist-rooted ‘Picual’ olive cuttings, grown in 2 L plastic pots containing perlite, were placed in a greenhouse between January and May with a temperature range of 20–30 8C. Plants were initially watered daily for 14 days. After buds were broken, plants began to be irrigated three times per week with 150 mL of a nutrient solution with the following composition: 2.5 mM KNO 3 , 1 mM MgSO 4 , 0.5 mM KH 2 PO 4 , 12.5 mM H 3 BO 3 , 1.0 mM MnSO 4 , 1.0 mM ZnSO 4 , 0.25 mM CuSO 4 , 0.2 mM (NH 4 ) 6 Mo 7 O 24 and 10 mM Fe-ethylenediamine-di-o- hydroxyphenylacetic acid (Fe-EDDHA) plus 0.5 mM Ca 2+ . After 25 days of acclimation, shoots were pruned to a single shoot per plant and four treatments were established. Eighty uniform plants were selected and arranged in a completely randomized experiment with 20 plant replications. Plants were irrigated with a saline nutrient solution with the following composition: 2.5 mM KNO 3 , 1 mM MgSO 4 , 0.5 mM KH 2 PO 4 , 12.5 mMH 3 BO 3 , 1.0 mM MnSO 4 , 1.0 mM ZnSO 4 , 0.25 mM CuSO 4 , 0.2 mM (NH 4 ) 6 Mo 7 O 24 and 10 mM Fe-EDDHA plus 75 mM NaCl, and the following different CaCl 2 concentrations for each treatment: 0, 2.5, 10 or 40 mM, respectively. The www.elsevier.com/locate/scihorti Scientia Horticulturae 109 (2006) 303–305 * Corresponding author. Tel.: +34 957 218 498; fax: +34 957 218 569. E-mail address: pa2mejij@uco.es (J.C. Melgar). 0304-4238/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2006.04.013