CO₂ elevation and chelation induced sunflower phytoremediation of copper-contaminated soil

【Objectives】The aim of this study was to investigate efficiency of sunflowers phytoremediation in copper-contaminated soil under different CO2 concentration levels and various chelating agents. Furthermore, this study aimed to screen CO2-sensitive cultivars of sunflowers, therefore, providing data tosupport the need for phytoremediation of copper-contaminated soil.【Methods】A pot experiment was conducted in artificial climate chambers under two CO2 concentration levels, normal (370 mol/mol) and elevated (800 mol/mol). Using a completely randomized design, five different cultivars of sunflowers in soil contaminated with 100 mg/kg Cu were treated with different concentrations of EDTA and DTPA to determine the effects of a chelating agent in combination with various levels of CO2 concentration on repair efficiency of sunflowers in Cu-contaminated soil.【Results】1) The extraction of Cu from the contaminated soil using different chelating agents is significantly different. Based on the low toxicity followed by high concentration of chelate when extracting Cu from contaminated soil, EDTA 3 mmol/kg soil and DTPA 5 mmol/kg soil are selected. 2) The loss of green in leaves and dehydration of sunflowers are relieved to some extent under the elevated CO2 concentration following the application of chelating agents. Furthermore, the total biomass amounts of Shikui-3 and Altai-2 are increased, while those of Shikui-4 and Altai-1 are decreased. 3) Soil pH values are increased in the treatments with chelating agents at both CO2 concentrations, and the extent of the increase in the DTPA treatments is significantly higher than that in the EDTA treatments. Although the elevated CO2 concentration has an impact on soil pH, there was no significant difference in soil pH between the two CO2 levels for the five sunflower cultivars. 4) The above-ground Cu accumulation in Shikui-4 and Altai-1 significantly decreased under conditions of elevated CO2.The Cu accumulation amounts in shoots of Shikui-3 and Youshengyin-2 are slightly increased under conditions of elevated CO2, while the amount in shoots of Altai-2 is significantly increased. The Cu concentrations of sunflower leaves and stems in the treatments with 5 mmol/kg soil DTPA under elevated CO2 conditions are increased by 239%-646% compared with the controls, and the Cu accumulation amounts of the plants are increased by 230%-362%. The results also show that the effect of Cu concentrations in stems and leaves of sunflowers are consistent. The mobilization of Cu in soils is more active in the DTPA treatments compared with the EDTA treatments.【Conclusions】Sunflower resistance to Cu can be enhanced to some extent under conditions of elevated CO2. Altai-2 is the most sensitive to elevated CO2 in 100 mg/kg Cu-contaminated soil. It is possible that the application of chelating agents is a main factor of affecting the soil pH change under conditions of elevated CO2. TheDTPA 5 mmol/kg treatment is more effective in the remediation of Cu-contaminated soil (100 mg/kg) under the elevated CO2 condition compared with EDTA 3 mmol/kg.