Effect of sodium chloride and cadmium interaction on some vegetative and physiological characteristics and Na and Cd uptake in roots and shoots of purslane (Portulaca oleraceae L.)

  Salinity, especially NaCl, is one of the most important abiotic stresses which limits crop productivity in dry regions like Iran. Also, soil and water heavy metal pollution is increasing in developing countries, which may suppress crop yield. The adverse effect of salinity on crop growth may be affected by soil cadmium content and vice versa. Purslane is one of the oldest and the most salt tolerant plant species having medicinal and edible uses in arid climates. Little is known about growth response of purslane to combined effect of NaCl and cadmium in soils. The aim of this study is to investigate the interaction of NaCl and cadmium on vegetative and physiological characteristics, sodium (Na) and cadmium (Cd) uptake and accumulation in roots and shoots of purslane. This experiment was arranged as factorial based on complete randomized design with four replications and conducted in growth chamber with 25/18 °C temperatures. Factors included growth medium NaCl concentration at four levels (0, 23.1, 57.4 and 100.2 mM) and cadmium at five levels (0, 0.5, 1, 2 and 4 mg/l). Seeds of purslane (local ecotype of Jiroft) were sown in 1-litre plastic pots filled with coco peat-perlite (2:1) and were watered until full emergence and establishment. Then, seedlings were treated with Hoagland solution containing calculated amounts of NaCl and cadmium until 87 days afterward. Significant decrease in shoot biomass started from 23.1 mM NaCl and 2 mg/l cadmium. Also, leaf greenness index (SPAD value) decreased with increase in salinity in each cadmium level; however, when no cadmium was applied, SPAD did not significantly decrease up to 57.4 mM NaCl. Similarly, salinity had no significant effect on leaf relative water content (RWC), but in each salinity level, RWC decreased with increased cadmium level. On the other hand, tissue electrolyte leakage significantly increased with NaCl concentration, however, increase in Cd concentration had no substantial effect on it. Shoot and root Na content linearly increased with salinity, but in each salinity and Cd level, contents of Na in roots were significantly higher than those of shoot. Same results were observed for shoot and root Cd content. Shoot Na content was not significantly affected by Cd concentration in growth medium until 2 mg/l Cd and only 4 mg/l Cd significantly increased it. Although sodium chloride and Cd contamination decreased purslane growth, but our results suggest that considerable accumulation of Na and Cd in roots of purslane inhibits excess translocation of Na and Cd to shoot tissues and further growth inhibition