Malic acid and Phosphorus Influences on Nickel Phytoremediation Efficiency and Metal Nutrients Relationships in a Ni-Polluted Calcareous Soil

ABSTRACT: Influence of malic acid and phosphorus (P) on nickel (Ni) phytoremediation was investigated in maize grown on a Ni-polluted calcareous soil. Addition of P levels increased shoot dry weight of maize in malic acid-treated and malic acid-untreated soil. Root dry weight of maize was also influenced by P levels in both malic acid-treated and malic acid-untreated conditions. The highest Ni uptake efficiency was observed with the addition of 60 mg P kg-1 in the absence of malic acid. Malic acid caused a considerable increase in Ni uptake efficiency only in control, where no P fertilizer was added. Malic acid was not effective at the levels 30 and 60 mg P Kg-1. Where 90 mg P kg-1 added to the soil, malic acid decreased Ni uptake efficiency. The value of Ni remediation factor, the percentage of Ni removed by plant shoot from the total Ni content in the soil, was affected by the addition of P levels or the application of malic acid. The low values of Ni remediation factor revealed that only a tiny proportion of this metal from its total content was removed throughout the phytoremediation. Ni uptake showed significant correlation coefficients with Zn, Cu and Mn uptake in maize shoot demonstrating synergistic relationships between the translocation from root to shoot of Ni with those of Zn, Cu and Mn. Significant correlation coefficients were observed between the uptake of Ni with those of Zn, Cu and Mn in maize root demonstrating synergistic relationships between the absorption of Ni with those of Zn, Cu and Mn.