Effects of magnetically treated Sedum alfredii seeds on the dissolved organic matter characteristics of Cd-contaminated soil during phytoextraction

The effects of magnetic field treatments on the two determining factors of phytoremediation, growth status and element uptake capacity, of Sedum alfredii Hance. have been thoroughly studied; however, minimal studies have been performed to determine the influence of the Cd hyperaccumulator S. alfredii, grown from magnetically treated seeds, on the dissolved organic matter (DOM) characteristics in its rhizosphere. A series of pot experiments were conducted to evaluate the variations in the DOM concentration and fractionations in the rhizosphere of S. alfredii treated with external magnetic fields. Compared with the untreated seeds, S. alfredii grown from magnetically treated seeds excreted more DOM in its rhizosphere. Additionally, the hydrophilic DOM fractionation proportion, which presented a greater capacity to mobilize Cd in the soil, increased from 42.7 % in the control sample to 47.2 % in the 150 mT magnetically treated S. alfredii sample. The water-soluble and exchangeable forms of Cd in the rhizosphere of the magnetically treated S. alfredii were significantly lower than those of the control sample. Furthermore, the Cd extraction capacity of DOM from the rhizosphere of the magnetically treated S. alfredii was greater than that of the control sample, thereby increasing the Cd uptake ability of the magnetically treated species. This study proves that a suitable magnetic field treatment can enhance the phytoremediation effect of S. alfredii, and reveals the mechanism of the phenomenon from the perspective of changes in soil DOM.