Exploring phytoremediation potential of willow NJU513 for cadmium-contaminated soil with and without epibrassinolide treatment

There has been a growing concern over soil cadmium (Cd) pollution, underscoring the importance of finding effective remediation strategies. Willow trees have emerged as promising candidates for phytoremediation of Cd-contaminated soils. Nevertheless, the specific potential of a novel willow genotype, NJU513, in remediating Cd-polluted soil remains unexplored. Hence, the primary objectives of this study were twofold: firstly, to ascertain the suitability of the willow genotype NJU513 for remediating Cd-contaminated soil; and secondly, to elevate its remediation efficciency with the application of epibrassinolide (Brs). In the pot-culture experiment without Brs, its leaf and stem Cd concentrations were 203 mg kg⁻¹ and 65.1 mg kg⁻¹, with a bioaccumulation factor (BCF) of 20.8 and 6.68, respectively. In the pot-culture experiment with Brs, the corresponding Cd concentrations were 226 mg kg⁻¹ and 59.2 mg kg⁻¹, with a BCF of 23.1 and 6.06, respectively. In addition, the extracted Cd contents were higher in the Brs treatments (1.11–1.37 mg plant⁻¹) than in the no-Brs treatments (0.78–0.96 mg plant⁻¹) because Brs increased the plant biomass and leaf BCF. The mechanism underlying the Cd accumulation of NJU513 leaves with and without Brs was revealed by a transcriptome analysis. The expression levels of genes related to metal ion binding, channel activity, and transporters in leaves were up-regulated, which contributed to the high Cd accumulation and stress tolerance. Analyses of soil metabolites and bacteria in the presence and absence of Brs spraying on willow leaves indicated that soil organic compounds with carboxyl and amino groups may induce Cd activation and passivation, respectively. This study provides valuable insights for developing woody plant varieties that can be used for remediating Cd-contaminated soil.