Physiological responses and lipidomic analysis underlying lithium tolerance in Cardamine violifolia

The rapid expansion of electronics and electric vehicle industries has substantially increased electronic waste generation, exacerbating soil and water lithium (Li) contamination. Despite growing environmental concerns, research on Li phytotoxicity mechanisms remains limited. This study investigated Li tolerance in Cardamine violifolia using controlled exposure to lithium chloride (LiCl) at concentrations of 50, 100, 200, and 400 mg L^-1. Key findings demonstrate that 400 mg L^-1 LiCl (a high-concentration exposure) significantly reduced biomass and total chlorophyll content by 37.1 % and 15.6 %, respectively; relative to control. Conversely, 100 mg L^-1 LiCl elevated total chlorophyll content by 8.5 %. Tissue Li accumulation exhibited concentration-dependent increases, reaching maximal values of 251.30 mg kg^-1 FW in shoots and 12.71 mg kg^-1 FW in roots under 400 mg L^-1 exposure. These accumulation levels represented 6.1-fold and 4.7-fold compared to those observed under 50 mg L^-1 LiCl treatment. Subcellular analysis revealed Li predominantly localized in cell walls (38.6-48.1 % in shoots; 53.0-64.4 % in roots) and soluble components (31.2-40.1 % in shoots; 15.9-29.3 % in roots), with the ethanol-extractable fraction (93.1-94.3 % in shoots; 85.8-90.8 % in roots) representing its dominant speciation form. Critically, lipidomic profiling indicated that C. violifolia enhances Li stress tolerance through shoot- and root-specific lipid remodeling: triacylglycerols (TG) mitigate toxicity via hydrophobic interactions and low phase transition properties, while ceramides (Cer) modulate root antioxidant systems. These results elucidate physiological and molecular adaptations underlying C. violifolia's exceptional Li tolerance, laying the groundwork for its further investigation in remediation of Li-contaminated soils.