Effects of foliar application of copper nanoparticles on the morphological and physio-biochemical traits of marigold (Tagetes patula L.) under salinity stress

This study aimed to assess how foliar application of copper nanoparticles (Cu-NPs) influences the growth, morpho-physiological and biochemical traits of marigold plants subjected to salt stress. The study was conducted in Poldakhtar, Iran, using a greenhouse pot-based factorial experiment arranged in a completely randomized design with three replicates. Two factors were tested: foliar application of copper nanoparticles (Cu-NPs) at concentrations of 0, 100, 200, and 400 mg L⁻¹, and salinity stress induced by sodium chloride at levels of 0, 30, 60, and 90 mM. The study revealed that increasing salinity levels caused significant reductions in key growth parameters including plant height, stem diameter, leaf number, chlorophyll and carotenoid content, relative water content, root length and volume, shoot and root biomass, as well as flower size and longevity, demonstrating the pronounced negative impact of salinity stress. Concurrently, salinity stress induced physiological responses including elevated electrolyte leakage, malondialdehyde and proline levels, along with enhanced activities of antioxidant enzymes (catalase, peroxidase, ascorbate peroxidase). Foliar application of copper nanoparticles (Cu-NPs) at 100-200 mg/L effectively mitigated these stress effects by enhancing antioxidant enzyme activities, increasing proline accumulation, improving water balance, and enhancing photosynthetic pigments. The 200 mg/L Cu-NP treatment showed optimal efficacy, improving salinity tolerance through these mechanisms and demonstrating strong potential for enhancing marigold productivity in saline soils.