The role of soil elemental forms in the soil-plant migration system: An example of heavy metals in Epimedium production areas

Investigating the heavy metal content and migration behavior in the soil and plant system of Epimedium origin is crucial for ensuring the safety and sustainable development of this valuable medicinal plant. The concentration of heavy metals in the soil of Epimedium was found to be highest in the residuel form (RS) and lowest in the water-soluble form (WS). Among the different parts of the Epimedium plant, leaves showed the highest content of Cr, Ni, Cu, As, and Pb with average contents of 0.02 mg.kg⁻¹, 0.01 mg.kg⁻¹, 0.11 mg.kg⁻¹, 0.16 mg.kg⁻¹, and 0.01 mg.kg⁻¹, respectively, and roots showed the highest content of Zn with average contents of 0.30 mg.kg⁻¹. The results of correlation analysis and linear fitting showed significant correlation and better linear fitting results between different parts of Epimedium (roots, stems and leaves) and various forms of heavy metals in soil. Among them, Zn (ion-exchange form) and Zn (leaf) showed the best fit with R² reaching 0.74. Results from random forest modeling indicated that the forms of heavy metals in soil, such as bound form, ion exchange form, and strong organic bound form, significantly influenced the distribution of heavy metals in roots, stems, and leaves of Epimedium. Overall, besides the readily available heavy metals in soil, other forms of heavy metals also play a critical role in the soil-plant migration system.