Environmental levels of microplastics disrupt growth and stress pathways in edible crops via species-specific mechanisms

Introduction Microplastics (MPs) are emerging contaminants in agricultural soils. However, the responses of different plant species to MP stress under soil conditions across varying concentration levels, as well as the underlying mechanisms, remain insufficiently understood. Methods This study examined the morphological, physiological, and biochemical responses of Chinese cabbage ( Brassica rapa ) and cherry radish ( Raphanus sativus ) grown in soil containing polystyrene microplastics (PS-MPs) at concentrations of 10, 50, and 100 mg/kg. Results PS-MPs altered soil properties by increasing pH and water-holding capacity (WHC), which promoted early germination in both species. However, during later growth stages, MPs inhibited development in a species-specific manner. In cherry radish, root length and fruit diameter decreased by 35.0% and 20.4%, respectively, primarily due to physical blockage. In Chinese cabbage, leaf area and petiole number declined by 35.9% and 41.7%, mainly driven by soil structural disruption and nutrient loss. Notably, the most pronounced effects occurred at low (10 mg/kg) to medium (50 mg/kg) concentrations, indicating a non-linear dose–response relationship. Hierarchical regression analysis (HRA) further revealed distinct toxicity mechanisms: physical accumulation and localized hypoxia were predominant in cherry radish, whereas oxidative stress and redox imbalance played a central role in Chinese cabbage. Discussion These findings support current ecotoxicological models and highlight the importance of plant–particle interactions in shaping crop responses. The results provide new insight into MP phytotoxicity and inform future risk assessments under realistic soil conditions.