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

IntroductionNickel (Ni) is an essential micronutrient required for optimal plant growth and development, but excessive Ni is toxic and threatens plant growth and productivity as well as human health. The removal of Ni from soil through phytoextraction is an ecofriendly technique for heavy metal remediation. But low bioavailability of metals in soil is often a limiting factor in phytoextraction. Ethylenediaminetetraacetic acid (EDTA) is recognized as a highly effective chelate that can increase soil mobility and uptake and translocation of heavy metals in plants. However, its long soil persistence time and its resistance to breakdown by soil microorganisms limits its efficiency for phytoremediation. The objective of this study was the evaluation of the effects of various concentrations of EDTA on the bioavailability of Ni in soil and the phytoremediation capacity of Ni in Calendula tripterocarpa plant.Materials and methodsIn 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 discussionThe 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.ConclusionIt 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.