Phytoremediation ability of nickel-contaminated soil using Sunflower (Helianthus annuus L.) and Sorghum (Sorghum bicolor L.)

Soil contamination due to heavy metals is one of the major environmental problems across the world, causing significant risks to public health and ecosystems. Phytoremediation is a low-cost and ecofriendly method, which can be applied to clean up contaminated soils. Appropriate plants for phytoremediation should be characterized by rapid growth, high biomass production, and tolerance to high concentrations of heavy metals in shoots. The main objectives of the current study were to 1) evaluate the effects of Nickel contamination on growth characteristics of sunflower and sorghum and 2) assess the ability of refining nickel contamination by sunflower and sorghum.
To study the capability of sunflower and sorghum plants in phytoremediation of Ni contaminated soils, a greenhouse experiment as factorial arranged in completely randomized design with three replications was carried out at Faculty of Agriculture, University of Tehran, Karaj, Iran in 2012. The experimental treatments consisted of two crop species, sunflower and sorghum, and four levels of nickel concentrations in the soil (0, 150, 300, and 450 mg of Ni per kg of soil). After 8 weeks from sowing date (flowering stage, R4), plants were harvested by cutting the shoots approximately 0.5 cm above the soil surface. Nickel, Fe, and Zn concentrations were determined using atomic absorption spectrophotometry. The analysis of variance for the obtained data was done by SAS v9.1 software.
Results showed that the highest values of shoot, root, and total dry matter (36.66, 29.77 and 66.43 g.plant-1, respectively) were related to sorghum plants grown in non-contaminated soil. Also, the lowest values of shoot, root, and total dry matter (8.39, 1.74 and 10.12 g.plant-1, respectively) were related to sunflower plants grown in 450 mg Ni per kg of soil. The maximum values of Ni uptake by total plant biomass and shoot part of plants (6.1 and .67 mg.plant-1, respectively) were observed in sorghum plants grown in 450 mg Ni per kg of soil. While, the minimum values of Ni uptake by total plant biomass and shoot part of plants (0.11 and 0.09 mg.plant-1, respectively) were observed in sunflower plants grown in non-contaminated soil.
Generally, results revealed that the capability of sorghum plant in phytoremediation of Ni contaminated soils was better than sunflower plant. In sorghum plants, low proportion of accumulated Ni in roots was translocated to shoot part. Therefore, sorghum plant can be used for ‘phytostabilization’. While, sunflower plants despite of relatively lower biomass, translocated higher proportion of Ni to shoot parts. So, sunflower can be suitable plant for phytoremediation of Ni contaminated soils (Phytoextraction).