Effects of NaCl salinity and CO2 enrichment on pepino (Solanum muricatum Ait.) - II. Leaf photosynthetic properties and gas exchange

One-month old, rooted semi-hardwood cutting plants of pepino cv. Xotus in s and-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 CO2 in controlled environment ch ambers during the last month of the experiment. Both NaCl salinity in the r hizosphere and atmospheric CO2 enrichment reduced the leaf content of total chlorophyll, chlorophyll a and chlorophyll b, as well as stomatal conducta nce and transpiration rate, but raised intercellular CO2 concentration and C2H4 emission of leaves. Minimal fluorescence yield, maximal fluorescence y ield, variable fluorescence yield of dark-adapted leaves, optimal quantum y ield and effective quantum yield of PS II, photochemical quenching coeffici ent, net photosynthetic rate, leaf water-potential, and photosynthetic wate r-use efficiency decreased under NaCl stress, but rose with an increase of the atmospheric CO2 concentration. In addition, the non-photochemical quenc hing coefficient and the dark respiration rate of leaves increased due to N aCl salinity and decreased at high CO2 conditions. On average, net photosyn thetic 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, bu t increased by 75-98% and 85-123% at 700 ppm CO2, and by 72-91% and 124-147 % at 1050 ppm CO2 in comparison with 350 ppm CO2 treatments. Under NaCl str ess, high CO2 improved photosynthetic water-use efficiency of leaves. (C) 1 999 Elsevier Science B.V. All rights reserved.