Freeze–Thaw Cycles Accelerate Plastic Pollution Invasion in Agriculture: Trojan Horse Effect of Microplastic–Plasticizer Contamination Revealed in Rye via Computational Chemistry and Multiomics

Climate change-related freeze-thaw (FT) cycles intensify combined contamination from diethyl phthalate (DEP) and microplastics (MPs) in agricultural systems. This study examines their synergistic phytotoxicity in hydroponic rye using multidisciplinary approaches, including physiology, transcriptomics, and computational modeling. FT dramatically increased cocontamination risks. Notably, DEP promoted MP uptake into plants by elevating MP surface charge─an effect intensified by FT─resulting in disrupted root function and nutrient absorption. Molecular analyses showed that DEP binds strongly to key proteins (e.g., HSP70; ΔG = -7.6 kcal/mol), inhibiting photosynthesis (net rate reduced by 20.1-64.5%) and altering antioxidant activity. MPs adsorbed DEP, reducing its mobility, while simultaneously reshaping the root microbiome to favor DEP-degrading bacteria (e.g., Rhizobium). Transcriptomic changes were observed in stress-responsive and phytohormone pathways. These results demonstrate that FT cycles exacerbate combined pollutant toxicity through surface charge modification, molecular disruption, and microbial community adaptation, offering important insights for assessing ecological risks under climate-induced stressors.