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