Morpho-physiological responses of purslane (Portulaca oleracea L.) to humic acid under Nickle stress

In order to investigate the morpho-physiological responses of purslane plant to humic acid under Nickle stress a split plot experiment based on a completely randomized design with two factors and three replications were carried out in the greenhouse. The factors were nickel concentrations with four levels (0, 0.2, 0.4 and 0.6 mM) as the main plots and four levels of humic acid concentrations (0, 200, 400 and 600 mg/L) as sub-main plots. The results showed that different nickel and humic acid concentrations had significant effects on most of morpho-physiological traits such as; root length, MDA, SOD, CAT chlorophyll and carotenoid contents. By increasing nickel levels, the growth indices such as shoot and root length, fresh and dry weight, chlorophyll, a, total chlorophyll and the amount of carotenoid decreased, while by increasing the nickel levels the proline content, MDA and CAT decreased. By increasing humic acid level, the proline content and the activity of CAT increased, while the amount of MDA and SOD enzymes decreased. The highest yield and chlorophyll and carotenoid contents was obtained at 0.4 mM nickel and 600 mg/L humic acid. However, it can be concluded that applying the humic acid can be a suitable procedure to reduce the harmful effects of nickel stress and improving in physiological and biochemical parameters and plant tolerance to nickel stress in Portulaca oleracea.