Effect of Arundo Donax L. Combined with Low-Molecular-Weight Organic Acids in Remediation of Cadmium-Contaminated Soil

To investigate the remediation efficiency of Arundo donax L. alone and its combined application with low-molecular-weight organic acids (LMWOAs) for cadmium(Cd) contaminated soil, a 180 day pot experiment was conducted. Six treatments included clean control (CK), Cd-contaminated control (CDG), low concentration of citric acid (LC-CA), high concentration of citric acid (HC-CA), low concentration of tartaric acid (LC-TA) and high concentration of tartaric acid (HC-TA) were set up. The growth response of Arundo donax L. under Cd stress, as well as the effects of different treatments on Cd uptake, translocation, accumulation and removal of Cd, were studied. The results showed that: ① At the tested Cd concentration, the growth of Arundo donax L. was slightly inhibited. The addition of citric acid and tartaric acid increased the biomass of Arundo donax L. and enhanced its Cd tolerance, with the most significant promoting effect on root biomass accumulation. ② Cd distribution in different organs of Arundo donax L. followed the order of root > stem > leaf. The Cd content in underground parts was 1.3~1.8 times that in aboveground parts, and the Cd removal amount of underground parts accounted for 58.1%~75.0% of the total removal amount, confirming that underground tissues were the main accumulation sites of Cd. ③ The application of LMWOAs improved the Cd extraction efficiency of Arundo donax L.. The Cd content in plants under LMWOAs treatments ranged from 3.36 to 4.49 mg·kg⁻¹, the translocation factor (TF) was 0.34~0.51, and the bioconcentration factor (BCF) was 0.45~0.66. ④ Significant differences existed in the effects of different organic acids: low-concentration citric acid showed the best promotion effect of Cd translocation; high-concentration tartaric acid exhibited the optimal enhancement on Cd accumulation; high-concentration citric acid effectively increased the total removal amount of Cd. In conclusion, the combined remediation of Cd-contaminated soil by Arundo donax L. with LMWOAs has good application potential. Different types and concentrations of organic acids can achieve differentiated remediation objectives: high-concentration citric acid is suitable for maximizing total Cd removal; low-concentration citric acid is suitable for enhancing Cd translocation to aboveground parts, which is beneficial to phytoextraction; high-concentration tartaric acid is suitable for enhancing Cd accumulation in roots, which is conducive to phytostabilization. In practical application, appropriate type and concentration ratio of organic acid can be selected flexibly according to remediation targets and subsequent utilization mode of Arundo donax L.. This study can provide a reference for the combined phytochemical remediation of heavy metal-contaminated soils.