Polystyrene nanoplastics increase tetracycline residues while aggravating nutrient dysregulation and ultrastructural damage in the roots of Chrysanthemum coronarium L.

Polystyrene nanoplastics (PS-NPs) and tetracycline (TC) increasingly co-occur in environments, raising concerns about their combined effects on edible plants. Previous studies have mainly focused on single-pollutant toxicity or isolated physiological endpoints, leaving the links among antibiotic retention, root-zone chemistry, nutrient status, and cellular injury unresolved. Here, Chrysanthemum coronarium L. was hydroponically exposed for 7 d to TC (10 mg L⁻¹), PS-NPs (5-15 mg L⁻¹), or their mixtures. PS-NPs increased parent TC residues measured in root tissues by 6.0-35.8%, cell wall represented the primary sink for TC within the subcellular fractions. Combined exposure reduced root fresh weight, aggravated ultrastructural damage, and decreased K, Ca, Fe, and Mg concentrations. Co-exposure also acidified the rhizosphere solution, increased dissolved organic carbon (DOC), altered fluorescent dissolved organic matter (DOM) characteristics, and reshaped bacterial community composition. Structural equation modeling revealed that changes in rhizosphere chemistry, particularly DOM dynamics, were the principal drivers influencing nutrient absorption and fresh weight reduction. Overall, PS-NPs enhanced TC retention in roots and intensified phytotoxicity, these findings provide mechanistic insight into how microplastic-antibiotic interactions regulate pollutant bioavailability, rhizosphere stability, and plant growth, emphasizing the importance of DOM in governing contaminant-nutrient interactions within plant systems.