Growth of Agropyron elongatum in a simulated nickel contaminated soil with lime stabilization

A greenhouse study was performed to evaluate the feasibility of using Agropyron elongatum and lime treatment for remediation of a simulated nickel (Ni) contaminated acidic soil. The acid soil was spiked with four levels of Ni, i.e., 0, 15, 50, and 100 mg Ni kg^-1 soil and the soil pH at each Ni level was adjusted to 4, 6 and 8 by liming with CaO. Addition of lime raised the soil pH and resulted in a decrease in concentrations of DTPA-extractable and water-soluble Ni in the soil, with a maximum reduction of 64 and 28 mg kg^-1, respectively at the highest level of Ni treatment as compared to the control without Ni treatment. In general, excessive Ni content in soil, especially at pH 4 inhibited the growth of Agropyron. Liming improved the growth condition and the highest dry weight yield of 12 g pot^-1 was obtained in soil spiked with 15 mg Ni kg^-1 at pH 6; and at the highest level of Ni, the dry weight yield increased from 0.48 to 5.96 g pot^-1 when the pH was increased from 4 to 6. However a further increase in pH to 8 did not improve plant yield because of the unavailability of nutrients at such a high pH. Nickel contents in plant were positively correlated to soil Ni contents at each respective pH level. Most of the Ni taken up by Agropyron was retained in the roots and the highest Ni uptake by plant was 3.9 mg pot^-1 in soil spiked with 100 mg Ni kg^-1 at pH 5.9, which was about 2.6% of total Ni added to the soil. This implies that Agropyron is not a hyperaccumulating species but is highly tolerant. Lime amendment together with the tolerant characteristic of Agropyron could provide a possible means to remediate Ni contaminated soils through phytostabilization.