Toxicity of Polystyrene Nanoplastics and Tributyl Phosphate to Rye under Freeze–Thaw Cycles: Implications for Crop Safety and Mechanistic Insights from Transcriptome and Root Microbiome

Climate-driven freeze–thaw (FT) cycles amplify the combined toxicity of polystyrene nanoplastics (PS) and tributyl phosphate (TBP) in crops. TBP is a common plasticizer. Our multiomics study reveals that PS and TBP form complexes via van der Waals forces, enhancing PS uptake in rye roots. Coexposure induces severe oxidative stress (H2O2: 1.35-, 4.71-fold → 9.04-fold), suppresses photosynthesis, and activates antioxidant defenses, with FT conditions intensifying these effects. TBP restructures the root endophytic microbiome, enriching TBP-degrading bacteria (Acidovorax, Massilia). Transcriptomic analysis identifies jasmonic and abscisic acid (ABA) signaling pathways as central coordinators of plant defense through reactive oxygen species (ROS) scavenging and metabolic reprogramming. These findings demonstrate that FT cycles exacerbate NPs-plasticizer toxicity through three interconnected mechanisms: physicochemical complex formation, root microbiome remodeling, and hormonal signaling crosstalk. The study provides crucial mechanistic insights for assessing climate-pollution risks in cold-region agriculture, highlighting the need to consider pollutant interactions under dynamic environmental conditions.