Effects of combined NaCl and CaCl2 salinity on photosynthetic parameters of barley grown in nutrient solution

The changes caused by NaCl− and CaCl₂-induced salinity on several leaf parameters have been measured in two cultivars of barley ( Hordeum vulgare L.) growing in a growth chamber in nutrient solution. Salinity was induced by adding to the nutrient solution equal weights of NaCl and CaCl₂, to obtain conductivities of 2, 6, 12, 19 and 26 dS m⁻¹. Salinity induced decreases in the leaf water potential and in the osmotic potential. Salinity did not induce significant changes in the relative photosynthetic pigment composition of barley leaves, the photosynthetic pigment stoichiometry for neoxanthin:violaxanthin cycle pigments:lutein:β-carotene:Chl b :Chl a being close to 3:6:14:12:25:100 (mol:mol). Salinity per se did not induce interconversions in the carotenoids within the violaxanthin cycle in most barley leaves. The PSII photochemistry of most barley leaves was unchanged by salinity. However, some apparently healthy leaves growing in high salinity exhibited sudden decreases in PSII photochemistry and increases in zeaxanthin (at the expense of violaxanthin), that preceded rapid leaf drying. Salinity induced significant changes in the slow part of the chlorophyll fluorescence induction curve from barley leaves.