Abstract:The intensification of cadmium (Cd) contamination in soil and the low efficiency of Cd reduction by sole application of natural materials have made material modification and compounding important approaches to achieving efficient remediation of Cd-contaminated soil. To this end, a pot experiment with lettuce was conducted to investigate the effects of the sole application of modified attapulgite and its combined application with straw biochar on soil physicochemical properties, soil Cd availability and speciation, as well as lettuce growth, development, and Cd absorption. The results indicated that the calcined and iron-modified attapulgite significantly reduced soil Cd availability by 47.50%-67.19%, the Cd content in lettuce by 31.82%-36.36%, and increased the lettuce dry weight by 8.45%-11.27% (P<0.05). The attapulgite combined with straw biochar significantly decreased soil Cd availability by 40.00%-72.50%, increased soil pH by 0.21–0.36 units, organic matter content (OM) by 13.10%-15.53%, electrical conductivity (EC) by 37.42%-50.10%, and cation exchange capacity (CEC) by 7.97%-12.75% (P<0.05), reduced the Cd content of lettuce by 28.79%-39.90%, and enhanced the dry weight of lettuce by 13.15%–21.13% (P<0.05). The best effect was obtained by the iron-modified attapulgite combined with straw biochar. This combination promoted the transformation of Cd from an active state to a stable state. The SEM analysis revealed that soil pH was the primary determinant directly influencing soil Cd availability, which in turn had a direct impact on Cd content in lettuce. Therefore, the combination of iron-modified attapulgite with straw biochar could significantly enhance soil pH, improve soil structure (by increasing OM, CEC, etc.), synergistically promote soil Cd stabilization and lettuce growth, and reduce soil Cd availability and Cd absorption in lettuce, demonstrating strong application potential for soil Cd pollution remediation.