[Effect and Mechanism of Water-soluble Chitosan Promoting Phytoremediation of Cd and/or Pb-contaminated Soils by <i>Sedum aizoon</i> L.]

A pot experiment was conducted to investigate the growth response, concentration, and transportation characteristics of Cd and Pb in <i>Sedum aizoon</i> L. in four typical Cd/Pb-contaminated soils from northern and southern China with the addition of different levels of water-soluble chitosan （WSC）. The effect of WSC on physicochemical properties, Cd and Pb forms, and functional groups in contaminated soils was determined to clarify the internal mechanism of WSC promoting Cd and Pb accumulation by <i>S. aizoon</i>. The results showed that WSC improved the physicochemical properties of rhizosphere soil by increasing alkaline nitrogen and organic matter contents and significantly reducing pH values. In addition, WSC significantly increased the acid-extractable Cd and Pb in contaminated soils by 16.3%-34.5% and 88.9%-272.4%, respectively. Fourier transform infrared spectra analysis showed that amino （-NH₂） and hydroxyl （-OH） groups in soils were significantly increased by adding WSC. Therefore, the coordination of Cd/Pb with -NH₂ and -OH may play important roles in forming complexes and mobilizing Cd/Pb in soils. Moreover, the improvement in the rhizosphere environment of contaminated soils by WSC contributed to promoting Cd and Pb accumulation by <i>S. aizoon</i>. WSC significantly increased the total Cd and Pb accumulation by 14.5%-72.1% and 55.0%-128.5%, respectively, without obvious growth inhibition. Therefore, it is feasible to apply WSC to promote Cd/Pb accumulation using <i>S. aizoon</i>, while the matching of WSC addition amount, soil pollution condition, and plant materials should be further considered in practical application.