Ornamental characters, ion accumulation and water status in Arbutus unedo seedlings irrigated with saline water and subsequent relief and transplanting

Abstract

Arbutus unedo seedlings were grown in a greenhouse and submitted to three irrigation treatments (salinity period) using solutions with an EC of 0.85 dS m −1 (control treatment), 5.45 dS m −1 (S1) and 9.45 dS m −1 (S2). After 16 weeks, growth and ornamental characters, leaf water potentials, gas exchange and ion concentrations were determined. After the salinity period, plants were exposed to a relief period for 1 month, whereby half of the plants were transplanted to field conditions and the other half into 24 cm diameter plastic pots. Salinity induced a significant decrease in shoot biomass and leaf area but root/shoot ratio was increased. Plant height was significantly inhibited by salinity. The ornamental characters were affected in the treated plants, with symptoms of salt injury, such as burning of leaf margin. Leaf water potentials decreased with increasing salinity, more significantly at predawn than at midday. The relationship between net photosynthesis ( P n) and leaf conductance ( g l) was linear for all treatments and the same values of P n are associated with lower values of g l for the saline treatments than for control treatment. The concentration of Cl − in leaves increased with increasing salinity and was higher than the corresponding concentration of Na +. Na + and Cl − contents were higher in the leaves than in the roots in both saline treatments. The K + and Ca 2+ levels were lower in the treated plants than in control plants and applied salinity reduced the K +/Na + ratio in leaves, stems and roots, the decrease being much greater for leaves than for roots. The Ca 2+/Na + ratio fell with salinity in all parts of the plants. At the end of the relief period leaf water potentials were recovered mainly in field conditions. S2 treatment showed lower values of P n and g l than control and S1 treatments in pot conditions and in field conditions S1 showed the lowest values for P n and g l.