The effect of EDTA on the growth and phytoremediation capacity of nickel in pot marigold (Calendula tripterocarpa Rupr.)

Materials and methods In this study, the effect of different concentrations of EDTA (0, 0.5, 1, 2 g kg-1 soil) was investigated on Calendula tripterocarpa exposed to various concentrations of nickel (0, 100, 150 mg/kg). The experiment was conducted in a completely randomized design with factorial arrangement with three replications in greenhouse. To stabilize Ni in soil, repeated cycles of saturation with distilled water was performed for 20 days. Then, EDTA was added to soil 15 days before cultivation. Seeds were sown in pots and plants grown in pots without EDTA and nickel was considered as control. After, 45 days, plants were harvested and fresh and dry weights of shoot and roots, the content of chlorophyll a, b (Chl a, Chl b), malondialdehyde (MDA) content, Ni concentration in shoot and roots, and available nickel of soil was measured and bioaccumulation factor (BAF), translocation factor and total Ni removal per pot were computed for All treatments. Results and discussion The results revealed that with increasing nickel concentration, the growth parameters and content of Chl a, Chl b significantly reduced but the content of MDA in roots increased in comparison to the control. In non-stress condition, applying concentration of 1 and 2 g kg-1 EDTA reduced the growth parameters and content of Chl a, Chl b while increased MDA content in roots. These results indicate the toxicity of higher dose of EDTA for Calendula tripterocarpa plants. Under 100 and 150 mg kg-1 Ni in soil, applying 0.5 g kg-1 EDTA, increased nickel concentration in the aerial parts (65 and 60.35%) and roots (35 and 29.44%), translocation factor (22.5 and 25.20%) and total Ni removal per pot (27.66 and 23.44%). Interestingly, the application of 1 and 2 g kg-1 EDTA, decreased available nickel concentration in soil as well as nickel concentration in roots and shoots and translocation factor in plants. In addition, these concentrations of EDTA considerably decreased the biomass of plants and consequently reduced total Ni removal per pot. Conclusion It can be concluded that application of 0.5 g kg-1 EDTA enhanced phytoremediation capacity of Calendula tripterocarpa. In contrast, higher concentrations of EDTA decreased available nickel concentration in soil and due to decreasing biomass and Ni concentration in roots and shoots, reduced total Ni removal per pot and impaired phytoextraction efficiency of Calendula tripterocarpa.