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Optimizing Acetic Acid Application Strategy Can Effectively Promote the Remediation Performance of Oilseed Sunflower on Cd-Contaminated Soils

Applying exogenous organic acids is an effective method to improve the remediation efficiency of Cd-contaminated soils. To investigate the effects of exogenous acetic acid on Cd forms in rhizosphere soils and phytoremediation performance for Cd-contaminated soils, a potted experiment was performed with oilseed sunflower as the extractive plant. Acetic acid was applied at 1, 2, 3, 4, 5, and 6 mmol/kg at 20, 30, 40, and 50 days after seedling emergence. Soil without acetic acid was used as a control (CK). Emblematic chemical properties and different Cd forms in rhizosphere soils were inspected. Results showed that adding acetic acids improved the biomass of shoot and root; it increased firstly and then decreased with the increase of acetic acid concentrations. For all treatments, acetic acids increased sucrase activity and catalase activity but decreased amylase activity in rhizosphere soils. At 30 or 40 days after seedling emergence, the exchangeable Cd content, Fe-Mn oxide Cd content, and organic Cd content were lower, while the carbonate Cd content was greater. Adding acetic acids improved the removal rate of Cd, and when 1 mmol/kg acetic acid was applied at 40 days after seedling emergence, it was increased by 60%, which was the highest compared to CK. RDA showed that catalase activity, sucrase activity, carbonate Cd, and pH could promote the growth of oilseed sunflower, while organic Cd, Fe-Mn oxide Cd, total Cd, exchangeable Cd, and amylase activity inhibited the growth of oilseed sunflower. These findings suggest that acetic acid can improve the efficiency of phytoremediation in Cd-contaminated soils. In particular, the treatment with 1 mmol/kg acetic acid at 40 days after seedling emergence had the most obvious effect.