Physiological effects of cerium oxide nanoparticles on the photosynthesis and water use efficiency of soybean (Glycine max (L.) Merr.)

Abstract

Widespread industrial uses of cerium oxide nanoparticles (CeO₂ NPs) and their unregulated disposal have raised concerns about their environmental consequences. While studies are abundant on the phyto-effects of CeO₂ NPs, detailed understanding of the impact of CeO₂ NPs on plant photosynthesis is still lacking. In addition, no studies have evaluated the effects of CeO₂ NPs on plant water use efficiency (WUE), a key parameter for crop yield. The goal of this study was to determine the impact of CeO₂ NPs with two different surface properties (uncoated and polyvinylpyrrolidone (PVP)-coated) on the photosynthesis and WUE of soybean at four different concentrations (0, 10, 100 and 500 mg kg⁻¹ dry soil). At the concentration of 100 mg kg⁻¹, both types of CeO₂ NPs stimulated plant growth and enhanced the photosynthesis rate by 54% for bare CeO₂ NPs and 36% for PVP-CeO₂ NPs. The maximum rate of Rubisco carboxylase activity represented by V_cmax also increased by 32% and 27%, respectively, for bare and PVP-coated CeO₂ NPs at this concentration during the 3 week treatment. Conversely, the net photosynthesis rate was reduced by about 36% for both nanoparticles at 500 mg kg⁻¹ CeO₂ NPs. In addition, CeO₂ NPs at concentrations >500 mg kg⁻¹ also inhibited Rubisco activity and interfered with CO₂ diffusion pathways. The results also confirmed that the physiological effects of CeO₂ NPs on soybean depend on both the concentration and surface coating properties of the nanoparticles.