Elevated CO₂ enhances growth and cyanide assimilation in nitrogen-deficient rice: A transcriptome and metabolomic...

Plants face multiple challenges from environmental pollutants and higher emissions of atmospheric CO₂. Therefore, a hydroponic-based experiment was used to explore the combined effects of elevated [CO₂] (700 ppm) and exogenous cyanide (CN^-) (3.0 mg CN/L) on rice seedlings under nitrogen deficiency, utilizing metabonomic and transcriptomic analysis. Elevated [CO₂] significantly improved the growth of CN^--treated rice seedlings compared to those with ambient [CO₂] (350 ppm), and it also significantly affected CN^- assimilation. Transcriptome analysis revealed distinct impacts on differentially expressed genes (DEGs) across treatments and tissues. KEGG analysis showed variability in DEGs enriched in amino acid (AA) and energy metabolism pathways due to elevated [CO₂] and CN^-. Metabonomic indicated that higher input of [CO₂] and exogenous CN^- more severely impacted energy metabolism elements than the individual species of AAs. Positive synergistic effects of elevated [CO₂] and CN^- were observed for glutamine and asparagine in shoots, and methionine in roots, wherein negative effects were noted for phenylalanine in shoots, and phenylalanine, valine, and alanine in roots. Meanwhile, positive effects on fumarate in shoots and α-ketoglutarate and succinate in roots were also found. Overall, elevated [CO₂] enhanced growth in CN^--treated rice seedlings under nitrogen deficiency by altering AA and energy metabolism. This is the first attempt to provide new evidence of [CO₂]-based gaseous fertilization as an energy-saving strategy for rice plants fed with biodegradable N-containing pollutants as a supporting N source under N deficient conditions.