Morphological, Physiological and Metabolomic Responses of Mulberry to Cadmium Exposure: Unveiling Dose‐Dependent Tolerance and Activation Mechanism

This study investigated the mechanisms of cadmium (Cd) tolerance and root exudate-mediated soil activation in mulberry (Morus alba L.), a promising species for phytoremediation. Hydroponic experiments with Cd-tolerant seedlings exposed to 5 and 50 mg/L Cd revealed a biphasic concentration-dependent response. Low Cd induced negligible biological effects, whereas high Cd triggered substantial disturbances across multiple biological levels, including morphological alterations, physiological dysregulation and disrupted elemental accumulation patterns. Metabolomic profiling indicated that Cd stress significantly altered the secretion patterns of 17 root exudate metabolites in mulberry, exemplified by the upregulation of sucrose, lactose and 4-acetylbutyric acid, and the downregulation of β-alanine and myo-inositol. Further pathway enrichment analysis linked these differential metabolites to 17 metabolic pathways, with carbohydrate and amino acid metabolism as the main Cd-responsive pathways, suggesting their core role in mediating mulberry's Cd resistance. Root exudates enhanced soil Cd mobilisation in a positive concentration-dependent yet negative time-dependent manner. Consequently, mulberry adapts to Cd stress via metabolic reprogramming of root exudates-a strategic trade-off that serves a dual role by enhancing plant tolerance while simultaneously increasing Cd bioavailability in the soil. This insight provides a foundational framework for phytoremediation, centred on exudate management and the selection of stress-tolerant varieties.