Field-scale differences in rhizosphere micro-characteristics of Cichorium intybus, Ixeris polycephala, sunflower, and Sedum alfredii in the phytoremediation of Cd-contaminated soil

Understanding the intricate interplay between Cd accumulation in plants and their rhizosphere micro-characteristics is important for the selection of plant species with profitable Cd phytoextraction and soil remediation efficiencies. This study investigated the differences in rhizosphere micro-ecological characteristics and Cd accumulation in chicory, Ixeris polycephala, sunflower, and Sedum alfredii in low-moderate Cd-contaminated soil. Data reveal that the dominant organic acids in rhizosphere soil that responded to Cd were oxalic and lactic acids in chicory and Ixeris polycephala, tartaric acid in sunflower, and succinic acid in Sedum alfredii. These unique organic acids could also influence the abundance of specific rhizobacterial communities in rhizosphere soil that were Sphingomonadaceae and Bradyrhizobiaceae in both Sedum alfredii (9.75 % and 2.56 %, respectively) and chicory (8.98 % and 2.82 %, respectively) rhizosphere soil, Xanthomonadaceae in both Sedum alfredii and Ixeris polycephala rhizosphere soil, and Gaiellaceae in chicory rhizosphere soil. In this case, the combined effects of the organic acids and unique rhizobacterial communities by plant species increased the bioavailable concentration of Cd in Sedum alfredii, Ixeris polycephala, and sunflower rhizosphere soil, while decreasing the Cd-DOM concentrations in chicory rhizosphere soil and the water-extractable Cd reduced by 88.02 % compared to the control. Though the capacity for Cd accumulation in the shoots of chicory was weaker than of Sedum alfredii but better than either Ixeris polycephala or sunflower, chicory presented better Cd translocation and harbored Cd mainly as the low toxic chemical form of pectates and proteins-bound Cd and Cd oxalate in its shoot. Generally, chicory, as an economic plant, is suitable for phytoremediation of low-moderate Cd-contaminated soil after Sedum alfredii.