Impacts of foliar-applied polystyrene nanoplastics with different surface charges on tetracycline accumulation, phytotoxicity, and the endophytic microbiota in Chrysanthemum coronarium L.

Plant leaves represent a critical interface for the deposition of atmospheric nanoplastics (NPs). However, the effects of foliar-deposited NPs on antibiotic uptake and phytotoxicity are still poorly understood. This study investigated the effects of foliar application of polystyrene (PS), carboxyl-polystyrene (PSC), and amino-polystyrene (PSN) NPs on Chrysanthemum coronarium L., focusing on NPs internalization, their modulation of root-zone tetracycline (TC) uptake, and associated phytotoxic responses. Results showed that positively charged PSN significantly reduced TC accumulation in both roots (by 20.7 %-23.2 %) and leaves (by 13.6 %-15.1 %), followed by PSC and PS. Conversely, TC promoted NP retention in stomata and induced stomatal deformation. PSN exerted stronger inhibition on iron uptake and chlorophyll synthesis than PSC or PS, ultimately suppressing plant biomass more significantly. Although catalase activity increased, superoxide dismutase was significantly suppressed under NP exposure. This imbalance in antioxidant defense resulted in marked accumulation of reactive oxygen species and elevated malondialdehyde content in both leaves and roots. Under TC stress, NP spraying further exacerbated growth inhibition and oxidative damage. Microbiome analysis revealed that PSN increased bacterial richness in leaves but reduced Shannon diversity in roots. While foliar NPs exposure had limited impact on alpha diversity in TC-treated plants, it significantly enhanced microbial evenness in leaves. Notably, all three NPs induced only minor changes in the abundance of the keystone genus Pseudomonas, regardless of TC treatment. Overall, these findings demonstrate that atmospheric NPs act as key co-pollutants that alter contaminant bioavailability, intensify phytotoxicity, and reshape the composition of endophytic microbial communities.