Study on the Enhancement of Amaranthus mangostanus in the Remediation of Cadmium Contaminated Soil by Biodegradable Chelating Agents GLDA and NTA

Chelating agents can improve the bioavailability of heavy metals in soil and the efficiency of hyperaccumulating plants to absorb and enrich heavy metals. In order to improve the efficiency of Cd extraction from soil by Cd hyperaccumulating plants, Amaranthus mangostanus was focused in this study. In addition, the effect of different concentrations of biodegradable chelating agents, glutamic acid N, N-diacetic acid (GLDA) and nitrilotriacetic acid (NTA) on the enrichment of Cd from soil by Amaranthus mangostanus was investigated through laboratory pot experiment. The results show that addition of 5.0 mmol·kg^-1 NTA and 2.5 or 5.0 mmol·kg^-1 GLDA could significantly increase the aboveground biomass of Amaranthus mangostanus. when the concentration of Cd in soil was 5 mg·kg^-1, and the increment was 44.12%, 17.12% and 8.00%, respectively. Both GLDA and NTA could effectively increase the Cd content in the aboveground parts of Amaranthus mangostanus. When 5 mmol·kg^-1 of GLDA and NTA were added to the soil with Cd concentration of 40 mg·kg^-1, Cd concentration in the aboveground parts of Amaranthus mangostanus could reach 100.88 and 63.08 mg·kg^-1, which was 2.46 and 1.54 times higher than that without chelating agents, respectively. Moreover, addition of 5 mmol·kg^-1 GLDA or NTA was more effective in increasing the Cd content in the aboveground parts of Amaranthus mangostanus compared to 2.5 mmol·kg^-1 GLDA or NTA. Applying chelating agents to the soil could effectively increase the total amount of Cd enrichment in Amaranthus mangostanus. When applying 5.0 mmol·kg^-1 GLDA to a soil with Cd content of 20 mg·kg^-1, the total Cd extraction by Amaranthus mangostanus reached the highest point of 613.86 μg·pot^-1, which was 1.4 times higher than that without chelating agent addition. Both GLDA and NTA could increase the available Cd content in soil, and promote the absorption and enrichment of Cd from soil Cd by Amaranthus mangostanus compared with NTA and GLDA. It was found that in soil with Cd content of 5 and 10 mg·kg^-1, the application of NTA was more effective than GLDA in increasing the total Cd extraction by Amaranthus mangostanus. While in soil with Cd content of 20, 30, and 40 mg·kg^-1, the application of GLDA was more effective than NTA. This study provides a theoretical basis and reference for improving the efficiency of Cd extraction by hyperaccumulating plants.