Effect of coexisting nutrient divalent cations on cadmium transport in soil-herbal crop systems

Cadmium (Cd) pollution in Chinese herbal medicines poses a serious risk to medication safety. Regulating Cd uptake, transport, and accumulation in plants through ion-ion interactions offers a novel, environmentally sustainable, and practical approach to address this issue. However, the effects and underlying mechanisms of coexisting divalent cations zinc (Zn), magnesium (Mg), and manganese (Mn) on Cd uptake by Ligusticum sinense cv. Chuanxiong (L. chuanxiong) have not been comprehensively studied or well understood. In this study, the application of coexisting these cations (Zn, Mg, Mn) could significantly promote the growth of L. chuanxiong (21.11%-36.04%) and change the mobility of Cd in the soil-crop system. Specifically, adding Zn decreased Cd content in soil and plants by 18.23% and 20.62%, respectively, while Mg increased it by 10.99% and 62.27%. Mn addition, however, had no significant effect. Similar trends in soil enzyme activity were also observed with Zn, Mg, and Mn treatments. Simultaneously, the findings explore how coexisting divalent cations influence plant physiological responses, including photosynthesis and antioxidant capacities, enabling L. chuanxiong to better manage Cd stress. This study underscores the potential of ion-to-ion interactions as an effective approach to mitigate Cd accumulation, offering a practical and sustainable solution for enhancing the safety of Chinese herbal medicines. Additionally, the effects of mixed cation applications on Cd dynamics are complex, shaped by interactions between ion types, dosages, and their specific properties. These insights provide a foundation for developing more effective remediation strategies for Cd-contaminated soils, particularly in the cultivation of medicinal plants.