Effects of NaCl salinity and CO 2 enrichment on pepino ( Solanum muricatum Ait.) : I. Growth and yield

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. NaCl salinity in the rhizosphere reduced growth of all the organs, but raised stem dry weight ratio and root dry weight ratio. In contrast, atmospheric CO 2 enrichment increased plant and fruit growth. Leaf dry weight ratio and fruit dry weight ratio rose, but stem dry weight ratio and root dry weight ratio decreased at high CO 2 levels. Daily expansion rate of leaf area, growth rate of side-shoot length, rate of plant dry mass production, and increased rate of fresh fruit weight decreased due to NaCl stress, but increased with CO 2 enrichment. Side-shoot diameter rose, whereas specific leaf area, leaf area ratio, and side-shoot dry weight ratio declined under both NaCl-stressed and CO 2-enriched conditions. In comparison with the 350 ppm CO 2 treatment without NaCl salinity in the rhizosphere, net assimilation rate and relative growth rate of plants were reduced by 8–13% and 16–32% due to NaCl salinity, and enhanced by 22–23% and 42–64% at 700 ppm CO 2, and by 36–44% and 64–101% at 1050 pm CO 2, respectively. The simultaneous treatments of NaCl salinity and high CO 2 resulted in indefinite effects on vegetative and reproductive growth as well as on dry mass production of different plant organs. Nevertheless, the negative impacts of NaCl stress on plant growth and fruit yield diminished at high CO 2 levels. Atmospheric CO 2 enrichment increased the tolerance of pepino to NaCl salinity in the root medium.