Melatonin application enhances the remediation of cadmium-contaminated soils by Cinnamomum camphora

Abstract

Cinnamomum camphora (C. camphora) is a tolerant plant with high potential for cadmium (Cd) uptake and resistance. However, it is still unclear how melatonin application regulates Cd absorption and detoxification in C. camphora, and whether the soil quality is improved after remediation. In this study, melatonin was applied at the concentration of 20 mg·kg⁻¹ soil to the Cd-contaminated soil planted with C. camphora. We aimed to investigate the effect of exogenous melatonin on Cd phytoextraction and detoxification in C. camphora by assessing physiological and biochemical responses. We found that melatonin application improved Cd content in C. camphora (p < 0.05), with a pronounced increase by 150 % in both stem phloem and leaves. Under Cd stress, melatonin application resulted in a Cd bioconcentration factor that was over 2-times higher, and Cd translocation factors from root to stem and from stem to vein which were increased to the level of 1.0. Exogenous melatonin also enhanced plant growth and photosynthesis under the 180-day Cd stress. In addition, melatonin promoted C. camphora to modify its antioxidant defense systems in response to various temporal stages of Cd stress. At the early stage, melatonin decreased malondialdehyde by >20 % and increased both proline and glutathione reduction by over 30 %. At the late stage, melatonin increased glutathione and soluble sugar by 46.0 % and 10.7 %, respectively. Peroxidase activity was stimulated by melatonin throughout the growth period (p < 0.05). In the remediated soil, melatonin application decreased soil respiration by 12.5 % and inhabited activities of urease, catalase, and dehydrogenase, indicating improved soil quality. Overall, our findings suggest that melatonin application can enhance Cd phytoextraction and detoxification in C. camphora from contaminated soils, providing new insights into applicable strategies for Cd phytoremediation.