Growing rice (Oryza sativa) aerobically reduces phytotoxicity, uptake, and transformation of CeO₂ nanoparticles

This study compared the impact and uptake of root-administered CeO₂ nanoparticles (NPs) in rice growing under flooded and aerobic soil conditions, which are two water regimes commonly used for rice cultivation. CeO₂ NPs at 100 mg/kg improved photosynthesis and plant growth by reducing the oxidative damage and enhancing plant tolerance to stress, while a higher concentration (500 mg/kg) of CeO₂ NPs negatively affected plant growth. More significant effects were observed under the flooded condition than under the aerobic condition. CeO₂ NPs of 100 and 500 mg/kg resulted in 78% and 70% higher accumulation of Ce in shoots under the flooded condition compared to the aerobic condition. CeO₂ NPs partially transformed to Ce(III) species in soils and plants under both conditions. A higher extent of transformation under the flooded condition, which was partly attributed to the lower soil pH and redox potential under the flooded condition, leads to higher plant uptake of Ce. A higher extent of transformation in rhizosphere soil was observed. A higher plant transpiration rate (TR) under flooded conditions resulted in a higher accumulation of CeO₂ species in shoots. This study, for the first time, reported that water regimes influenced the biotransformation of CeO₂ NPs and their uptake and impact in rice plants.