Foliar application of 2,4-dichlorophenoxyacetic acid promotes cadmium phytoextraction by Celosia argentea Linn

The efficiency of phytoextraction highly depends on the growth of accumulating plants. To enhance cadmium (Cd) phytoextraction, 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin, was applied foliarly to Celosia argentea Linn. The results showed that foliar application of 2,4-D induced hormesis effect which enhanced the growth of C. argentea. At an application rate of 1.0 mg/L, 2,4-D treatment most significantly increased the growth of C. argentea (p < 0.05). The increase in growth may be linked to changes in endogenous hormone balance induced by 2,4-D. After treatment with 1.0 mg/L 2,4-D, a significant decrease in abscisic acid (ABA), Jasmonic acid (JA) and trans-Zeatin-riboside (tZR) levels and a significant increase in indole-3-butyric acid (IBA), 3-Indolepropionic acid (IPA) and 6-Benzylaminopurine (BAP) levels were observed in C. argentea. Specifically, the reductions in ABA and JA may be correlated with a decrease in stomatal closure on the leaf surface and increases in IPA and BAP may support root and plant growth development. Furthermore, a low concentration of 2,4-D significantly increased the uptake and translocation of Cd in C. argentea. At 1.0 mg/L treatment, Cd phytoextraction efficiency increased by 108 %. Residues of 2,4-D in soil were below 0.01 mg/kg after 7 days when applied foliarly at 1.0 mg/L. These findings suggest that foliar application of low-dose 2,4-D is a simple, efficient, and environmentally safe method to improve Cd phytoextraction efficiency in contaminated soils.