Biochar-assisted copper removal and metabolic responses of Hydrocotyle vulgaris in a hydroponic system: Insights from untargeted metabolomics and computational modeling

Biochar-assisted phytoremediation has potential for improving copper (Cu) removal, but the plant metabolic responses associated with biochar amendment remain insufficiently understood. Here, we established a biochar-Hydrocotyle vulgaris L. hydroponic system to evaluate Cu removal performance and associated plant physiological responses under controlled Cu exposure. Addition of 0.5 g corn-stalk biochar enhanced Cu removal and alleviated photosynthetic inhibition and oxidative damage at low-to-moderate Cu concentrations. Untargeted metabolomics indicated that biochar exposure was associated with metabolic reprogramming, involving energy metabolism and secondary metabolite biosynthesis. Notably, α-linolenic acid/jasmonic acid (JA) signaling were identified as candidate regulators for mitigating oxidative stress. Exogenous methyl jasmonate (MeJA) was further applied as an experimental signal-enhancement treatment, which improved photosynthetic pigment levels and reduced MDA under high Cu stress. Molecular docking and 100 ns molecular dynamics simulations supported the potential stability of JA-COI1 interactions. These results provide mechanistic insight into biochar-assisted Cu tolerance in a hydroponic plant system and may inform future water-based remediation strategies.