Enhancing photosynthesis and starch accumulation enable Torreya grandis seedlings to benefit from CO2 enrichment and warming

Elevated CO 2 levels and increased temperatures are two driving forces of climate change. Plants, including economic forest tree species, will confront the challenge of the combined effects of these two environmental factors under future climate conditions. This study focused on analyzing the influence of CO 2 (ambient 400 μmol mol −1 ; elevated 800 μmol mol −1 ) and atmospheric temperature (current 25 °C; future warming 29 °C) treatments on the photosynthetic characteristics and non-structural carbohydrates of precious subtropical nut tree species Torreya grandis seedlings. The findings suggested that Torreya exhibited greater sensitivity to elevated CO 2 than to warming. Elevated CO 2 boosted the seedlings’ maximum carboxylation rate of Rubisco (from 48.3 to 67.9 µmol m − 2 s − 1 ) and photosynthetic rate (from 5.1 to 13.3 µmol m − 2 s − 1 ), while reducing leaf nitrogen concentration. The increased activities of carbonic anhydrase and phosphoenolpyruvate carboxylase under elevated CO 2 might reconcile the contradiction between low leaf nitrogen levels and high photosynthetic capacity. The accumulation of starch and soluble sugars, primarily starch, led to a significant increase in non-structural carbohydrates in Torreya . Elevated CO₂ increased the starch content in Torreya leaves by approximately fourfold and the activity of ADP-glucose pyrophosphorylase by roughly threefold. This suggested that Torreya appeared to utilize starch as a carbon sink for storing photosynthates, while maintaining a lower soluble sugar/starch ratio to prevent the inhibition of photosynthesis by the accumulation of photosynthates. In summary, under elevated CO 2 and increased temperature, Torreya seedlings fixed more CO 2 by enhancing photosynthesis and carbon metabolism. Our findings suggested that Torreya might benefit under future climate conditions. • The response of Torreya to elevated CO 2 is greater than its response to warming. • Elevated CO 2 and temperature stimulate photosynthetic efficiency and starch production in Torreya . • Starch appears to function as a carbon sink for storing photosynthates, enabling Torreya to benefit from elevated CO 2 . • The plasticity of photosynthesis and carbon metabolism in Torreya enhances its adaptability significantly.