Different oxide nanoparticles enhancing salt tolerance in Cyclocarya paliurus via specific antioxidant strategies

Salt stress is an increasing environmental constraint on plant growth and productivity globally. As a multi-function tree species, Cyclocarya paliurus has attracted increasing attention for harvesting its leaf bioactive substances but shows limited salt tolerance. Although nanobiology has developed rapidly, it remains unclear whether different nanoparticles (NPs) elicit distinct antioxidant strategies in woody species under salt stress. To address this gap, we established an experiment under simulated natural conditions to investigate the phenotypic, physiological and molecular responses of C. paliurus to the application of three oxide NPs (ZnO-, MnO₂- and SiO₂-NPs). By combining WGCNA, copula graphical models (CGM), and PLS-PM, we developed the first CGM-PLS-PM framework to mechanistically resolve NP-specific stress responses in C. paliurus. Salt stress caused pronounced growth inhibition and strong accumulation of H₂O₂, O₂^•- and MDA (94-226%). All oxide NPs mitigated oxidative injury (24-57% ROS reduction) but operated through three differential antioxidant strategies. ZnO-NPs activated ARR-B-WRKY-bZIP regulators and enhanced SOD, CAT and POD by 58-127%, forming a rapid ROS-interception response. MnO₂-NPs upregulated APX-MDHAR-DHAR-GR (1.2-6.6-fold) and expanded AsA-GSH pools (2.1-9.5-fold), strengthening enzymatic redox regeneration processes. SiO₂-NPs induced MYB-bHLH modules and PAL-CHS-FLS, elevating total flavonoids by 49% and establishing a metabolic buffering response. CGM identified NP-specific gene-metabolite-trait hubs, and PLS-PM quantified their divergent causal contributions. Our results provide the first systems-level evidence that oxide NPs reconfigure antioxidant networks in a woody medicinal species, offering a mechanistic basis for optimizing oxide NPs applications that enhance salt tolerance while maintaining phytochemical quality.