Turning the enemy into an ally: Phytoremediation potential of Solidago canadensis L. for Cd-contaminated soil as influenced by microplastics and biochar

). Results revealed complex polymer- and dose-dependent effects on Cd dynamics, where PES enhanced Cd immobilization, while 0.2% PET/PLA paradoxically increased root Cd accumulation by 5.6%-13.8% despite reducing soil Cd extractability. MPs exposure induced comprehensive physiological perturbations in S. canadensis, including biomass allocation, chlorophyll degradation, micronutrient homeostasis, and profound metabolic reprogramming characterized by the upregulation of allelopathic metabolites. BC amendment effectively immobilized Cd, mitigated oxidative stress, and restored nutrient cycling by enhancing enzyme activities. Crucially, BC decreased the relative abundances of key allelochemicals by 65.3% ± 14.2% through energy metabolic restructuring, while maintaining high phytoremediation efficiency. Significant triple interactions (MPs type × MPs dose × BC) underscored context-dependency of remediation outcomes, with biodegradable PLA exhibiting distinct ecological implications. These findings demonstrate that integrating BC amendment with S. canadensis phytoremediation offers a sustainable strategy for managing MPs-Cd co-contaminated soils within the framework of ecological security.