Photoaging-driven amplification of polystyrene microplastic toxicity in wheat: physiological and multi-omics insights

Microplastics (MPs) in agroecosystems displayed phytotoxicity; however, the differential effects of pristine and photoaged MPs remain unclear. Herein, we examined the effects and mechanisms of polystyrene (PS) MPs on wheat ( Triticum aestivum L .) based on pristine and photoaged treatments. The results showed that photoaging significantly amplified the toxicity of PSMPs. Compared to pristine PS, photoaged PS reduced plant height by −20.4% and −30.6% under the T25 and T100 mg/L treatments, respectively, and biomass by −26.4% and −35.8%, with lowering chlorophyll content and elevating oxidative stress markers, including malondialdehyde, superoxide dismutase, peroxidase, catalase, and reactive oxygen species. Photoaged PS underwent surface modifications, including increased surface roughness, oxidation (1.53-fold increase), and negative charge. These changes promoted their adsorption capacity toward nutrient ions, leading to micronutrient depletion in the root zone and reduced nutrient accumulation in plant tissues. Integrated metabolomic-transcriptomic analyses revealed tissue - specific pathway enrichment underlying this difference in toxicity. Photoaged PS primarily affected carbohydrate/amino acid metabolism (starch and sucrose metabolism, glycerolipid metabolism) in shoots and signaling/lipid metabolism (glutamatergic synapse, linoleic acid metabolism) in roots. These integrated analyses elucidated the molecular mechanisms underlying the contrasting responses. Overall, photoaging increased PSMPs phytotoxicity by enhancing surface oxidation, disrupting nutrient uptake, and inducing tissue-specific molecular reprogramming.