Effects of NaCl salinity and CO 2 enrichment on pepino ( Solanum muricatum Ait.) : II. Leaf photosynthetic properties and gas exchange

Abstract

One-month old, rooted semi-hardwood cutting plants of pepino cv. Xotus in sand-potted culture were treated with 200 ml Hoagland nutrient solution with or without additional 25 mM NaCl twice a week for 2 months, and exposed to 350 ± 10, 700 ± 10 or 1050 ± 10 ppm CO 2 in controlled environment chambers during the last month of the experiment. Both NaCl salinity in the rhizosphere and atmospheric CO 2 enrichment reduced the leaf content of total chlorophyll, chlorophyll a and chlorophyll b, as well as stomatal conductance and transpiration rate, but raised intercellular CO 2 concentration and C 2H 4 emission of leaves. Minimal fluorescence yield, maximal fluorescence yield, variable fluorescence yield of dark-adapted leaves, optimal quantum yield and effective quantum yield of PS II, photochemical quenching coefficient, net photosynthetic rate, leaf water-potential, and photosynthetic water-use efficiency decreased under NaCl stress, but rose with an increase of the atmospheric CO 2 concentration. In addition, the non-photochemical quenching coefficient and the dark respiration rate of leaves increased due to NaCl salinity and decreased at high CO 2 conditions. On average, net photosynthetic rate and photosynthetic water-use efficiency of leaves decreased by 26–35% and 19–29% due to the presence of NaCl stress in the root medium, but increased by 75–98% and 85–123% at 700 ppm CO 2, and by 72–91% and 124–147% at 1050 ppm CO 2 in comparison with 350 ppm CO 2 treatments. Under NaCl stress, high CO 2 improved photosynthetic water-use efficiency of leaves.