Nutrient strengthening and stress alleviation in rice (Oryza sativa L.) via foliar ceria nanoparticles and biochar amendment under elevated CO2-mediated warming.

Elevated CO2 and rising temperature pose a significant challenge to global food security and nutrient acquisition by influencing rhizosphere bacterial community dynamics and physiological function in plants. Biochar has emerged as a potential solution to environmental and agricultural challenges. Nevertheless, its combined application with advanced materials like cerium oxide nanoparticles (CeO2-NPs) in rice cultivation under elevated CO2-mediated warming, particularly concerning bacterial community and nutrient acquisition, remains largely unexplored. To address this, rice plants were grown to examine the effect of biochar (1.5 %) and CeO2-NPs (100 mg/L) (BC-NPs), both individually and in combination, in an open-top chamber (OTCs) under present and future environmental conditions, simulating current and projected increases in CO2 and temperature. The combined application of BC-NPs significantly improved rice growth attributes, photosynthetic parameters, and antioxidative enzyme activities, while elevated conditions negatively influenced these parameters. Under elevated conditions, some key bacterial abundances declined, particularly Proteobacteria, Bacteroidetes, Desulfobacterota, and Gemmatimonadetes. BC-NPs application increased the abundance of these phyla. However, Simpson's index decreased under BC-NPs application, indicating a reduction in bacterial diversity. Compared to ambient conditions, elevated conditions led to reduced Zn, Cu, Ca, K, Mg, and Mn content in roots, shoots, and grains, accompanied by the downregulation of nutrient transporter genes (OsHMA5, OsYSL9, OsMTP8.1, OsMGT, and OsHAK1, OsZIP1) expression, except for YSL2. However, BC-NPs treatment synergistically increased nutrient content and upregulated nutrient transporter gene expressions by improving soil physicochemical properties, increasing the abundance of the beneficial bacterial community, and influencing plant physiological processes under elevated conditions. Overall, this study highlights the potential of BC-NPs as an effective approach to enhance nutrient acquisition and improve crop resilience under changing climatic scenarios.