Sex-dependent physiological and molecular responses of Salix variegata to polystyrene nanoplastics: an organ-resolved analysis

Polystyrene nanoplastics (PS-NPs) are emerging abiotic stressors, but their effects in dioecious woody plants and the role of plant sex remain poorly understood. Female and male cuttings of Salix variegata were hydroponically exposed to nominal 100-nm PS-NPs (0, 10, 50, and 100 mg L −1 ) for 21 d in 1/2-strength Hoagland nutrient solution. PS-NPs aggregated more strongly in nutrient solution than in ultrapure water, indicating that matrix-conditioned particle behavior should constrain interpretation. Across the concentration gradient, shoot growth and net photosynthetic rate changed little, whereas root architectural traits, stomatal-related variables, and oxidative/antioxidant endpoints were more responsive. Root architectural responses were broadly shared between sexes, but oxidative and antioxidant endpoints showed significant Sex × Concentration interactions in leaves and roots. Transcriptomic and metabolomic profiling at 100 mg L −1 revealed pronounced sex-associated interaction patterns, especially in leaves, where threshold-defined sex-restricted responses exceeded opposite-direction responses. Transcriptomic enrichment, metabolomic pathway mapping, pathway-level concordance analysis, and WGCNA together prioritized phenylpropanoid-associated metabolism as a candidate response axis linking secondary metabolism, redox-related processes, and sex-associated divergence. However, the data do not demonstrate direct cell-wall structural remodeling or field-scale ecological risk. These results show that nutrient-solution-conditioned PS-NP exposure induces sex-dependent and organ-resolved physiological, oxidative, and molecular reprogramming in S. variegata , highlighting the need to consider plant sex and organ context when interpreting woody-plant responses to nanoplastic stress.