Green-synthesized ZnO nanoparticles combined with fulvic and ascorbic acid strengthen antioxidant responses in sweet corn under salinity stress

Abstract

Soil salinity raises reactive oxygen species and limits crop performance. Green-synthesized zinc oxide nanoparticles (ZnO NPs) may help, but whether combining them with fulvic acid or ascorbic acid adds real benefit is unclear. We measured oxidative stress and antioxidant responses in sweet corn under non-saline and saline conditions across nine treatments: an untreated control, foliar or irrigation-applied ZnO NPs, ZnO NPs combined with fulvic acid or ascorbic acid, and each organic acid applied alone. We tracked leaf hydrogen peroxide (H 2 O 2 ), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Salinity, treatment, and their interaction significantly affected H 2 O 2 , SOD, and CAT (p < 0.001). POD showed significant treatment and interaction effects (p < 0.001) but no significant salinity main effect (p = 0.135). Salinity raised H 2 O 2 in the untreated control by 68.5%. Under salinity, irrigation-applied ZnO NPs with ascorbic acid cut H 2 O 2 by 66.2%, and the foliar combinations with fulvic acid and ascorbic acid cut it by 65.6% and 64.8%. Foliar ZnO NPs with ascorbic acid raised SOD by 41% and CAT by 132.6% relative to the saline control, giving the strongest combined SOD-CAT response. Foliar ZnO NPs combined with ascorbic acid produced high SOD and CAT responses and low H 2 O 2 accumulation. Foliar ZnO NPs combined with fulvic acid and irrigation-applied ZnO NPs combined with ascorbic acid also produced significant biochemical responses under salinity. These responses depended on formulation and application method.