Characteristics of cadmium accumulation in tobacco under field conditions and their enhancement strategies

Tobacco, with its substantial biomass and strong cadmium (Cd) enrichment capacity, is a potential candidate for phytoremediation of Cd-contaminated soil. However, its Cd accumulation characteristics under field conditions remain unclear. In this study, a field experiment (soil Cd concentration: 0.9 mg·kg⁻¹) demonstrated that the Cd accumulation per tobacco plant reached 1148.1 μg, with a dry biomass of 432.2 g in the mowing treatment. Cd was detected in all parts of the tobacco plant, with the highest concentration found in the leaf mesophyll (7.0 mg·kg⁻¹), and the predominant Cd chemical form was the less toxic NaCl-extractable fraction, which may be associated with the plant's Cd detoxification mechanism. Additionally, the Cd concentration was higher in the lateral roots than in the main roots, higher in the stem phloem than in the xylem, and a certain amount of Cd was also present in the flowers. Compared to 60 d after transplanting, the Cd concentrations in leaves, stems and roots, as well as the total and available Cd concentrations in rhizosphere soil, were significantly reduced at 180 d after transplanting. This decline may be attributed to Cd depletion in the rhizosphere soil and dilution effects caused by rapid plant growth. Nevertheless, the total Cd accumulation per plant at 180 d was significantly higher than that at 60 d. Mowing measures increased leaf dry biomass by 1.6 times, consequently enhancing total Cd accumulation by 1.6 times. These results provide a theoretical foundation for the practical application of tobacco in remediating Cd-contaminated soil.