●Dynamic changes of rice sheath non-structural carbohydrates and source-sink balance under elevated atmospheric CO2 concentration and temperature stresses

Rising CO₂ levels and temperatures significantly affect rice yield and quality by altering key physiological processes. As vital carbon reserves, non-structural carbohydrates (NSC) maintain the source-sink balance, directly influencing grain filling and food security. This study simulated high CO₂ and temperature conditions using open-top chambers with four treatment groups: control (ACT, ambient CO₂ at 415 ppm and temperature), elevated CO₂ (EC, 600 ppm CO₂), elevated temperature (ET, ambient +2°C), and combined CO₂ and temperature elevation (ECT, 600 ppm CO₂ +2°C). NSC concentrations, along with key physiological indexes such as leaf nitrogen and antioxidant enzyme activity, and gene expression, was measured to assess climate impacts on japonica rice variety “Nanjing 9108” physiology and source-sink balance. This study found that EC enhanced NSC concentrations, increasing soluble sugars and starch by 6.33% and 9.86% at heading, raising stem sheath NSC by 9.30%. Conversely, ET reduced sugars and starch by 16.67% and 6.24%, leading to a 7.75% NSC decrease. Under ECT, NSC levels dropped by 1.07%. Nitrogen concentrations in leaves, stem sheaths, and panicles declined under both EC and ET, EC reduced leaf nitrogen by 16.26%, while ET lowered nitrogen in stem sheaths and panicles by 17.29% and 16.53%. EC upregulated OsSUT1 and OsSUT2 gene expression by 69.55% and 131.85%, boosting carbon transport, whereas ET suppressed those genes, reducing grain carbon supply. Overall, elevated CO₂ improves NSC accumulation and transport, enhancing yield potential, while elevated temperature hinders these processes. Managing NSC and nitrogen dynamics is crucial to ensure stable rice yields under climate change.