Effects of different organic amendments on soil cadmium availability and phytostabilization by poplar

Cadmium (Cd) contamination in soil poses serious environmental risks. Phytostabilization with fast-growing species like poplar offers a sustainable solution. The addition of soil organic amendments, including pig manure (PM), wheat straw (WS), and biochar (BC), may affect soil Cd availability and the phytoremediation efficiency of poplar. The results revealed that the order of dissolved organic carbon (DOC) content during poplar growth was PM > WS > BC > CK (without soil organic amendments). From the 8th week, the water-soluble Cd content in the soils treated with PM, WS, and BC was notably lower than that in CK (P < 0.05). After 4 months of poplar growth, compared with CK, the addition of soil organic amendments reduced the proportion of exchangeable Cd in the soil and increased the ratios of carbonate-bound, Fe-Mn-oxidized, organic-bound, and residual Cd in the soil. The poplar grew and adapted well to soil contaminated with Cd, as evidenced by the 100% survival rate. At each Cd level, the accumulation of Cd was highest in the roots compared to stems and leaves. Especially, compared with the other soil organic amendments, PM increased the dry biomass of the poplar to 4.86 ± 1.08 g and accumulated 0.31 ± 0.11 mg of Cd. These findings suggest that pig manure may serve as a low-cost and effective amendment for poplar-based phytostabilization in moderately to highly Cd-contaminated soils.