The Addition of Degradable Activators Enhances Sedum alfredii Phytoremediation Efficiency in Cd-Contaminated Soils

Soil cadmium (Cd) pollution is a critical environmental issue that requires urgent remediation. Sedum alfredii Hance, known for its high biomass, strong stress tolerance, and suitability for harvesting, serves as an excellent hyperaccumulator. This study used field experiments to investigate the enhancement of Cd phytoremediation in soil using three activators: citric acid (CA), malic acid (MA), and polyaspartic acid (PASP). The results showed that the biomass of Sedum alfredii was increased by 8.95–28.37% by the addition of these activators, significantly boosting its Cd accumulation efficiency, with an average removal rate increase of 12%. Among all activators, CA exhibited the most substantial enhancement effect, with enrichment coefficients of 36.26% and 11.56% for the aboveground parts and roots of Sedum alfredii, respectively, and a 21.15% increase in the Cd removal rate. Although PASP had a less pronounced effect on biomass and Cd uptake, with decreases of 15.25% and 35.34% in the aboveground parts and roots, respectively, it significantly impacted soil Cd speciation and increased the activation rate by 20%.