Mineral composition and chlorophyll fluorescence in cowpea plants amended with bulk and nanoparticles of Zn and Cu oxides

Abstract

Zinc oxide (ZnO-NP) and copper (CuO-NP) nanoparticles have been proposed for crop fertilization, but studies demonstrating their efficiencies and evaluating their phytotoxicities compared to bulk sources are still scarce. Here, we assessed the dissolution of Zn and Cu oxides of nanoparticulate and bulk sources and their effects on cowpea’s biomass, nutritional status, and photosynthetic apparatus. The results showed that Zn and Cu dissolution rate and release from nanoparticulate oxides were higher than bulk oxides. Regardless of the source, the addition of Zn and Cu concentrations to the solution increased the root, stem, and leaf tissue concentrations of these micronutrients and reduced the contents of nutrients and pigments, with consequent inhibition of photosynthesis as indicated by the parameters of chlorophyll fluorescence. Except for the lowest rate of the sources tested, biomass was reduced due to metal toxicity. However, biomass decreasing was not related to the source itself but to the nanoparticle source higher solubility, which promoted higher phytotoxicity.