Adsorption behavior of carbon dots on La3+ and the multiple effects on the growth of mung bean seedlings under La3+ stress

The excessive use of rare earth elements (REEs) as micro-fertilizers is harmful to agricultural production and the environment. This study explored the potential application of carbon dots (CDs) to mitigate the effects of La contamination. The results indicate that the CDs based on citric acid (C-CDs) can adsorb La3+ in an aqueous solution system through surface carboxyl and pyrrolic-N. While no significant alteration in the total La content within mung bean seedlings was observed, the presence of C-CDs induced the conversion of La into an inactive form within the body and significantly affected the chemical form and distribution of La in the plant body. However, with increased concentrations, C-CDs do not effectively improve growth inhibition of the seedlings under La stress but exacerbate it. This may be relevant to the peroxidation damage and excess extracellular precipitates. RNA-seq results showed stronger cell wall-related synthesis under C-CD and La co-treatment than in La treatment, which indicated the important role of the cell wall in this process. Although many issues remain to be addressed, this study demonstrates that C-CDs possess distinct advantages in remediating soil La contamination without significantly impeding the plant's La absorption, thus exhibiting considerable potential for agricultural application.