Nitrogen assimilation and transpiration: key processes conditioning responsiveness of wheat to elevated [CO2] and temperature

Although climate scenarios have predicted an increase in CO₂] and temperature conditions, to date few experiments have focused on the interaction of CO₂] and temperature effects in wheat development. Recent evidence suggests that photosynthetic acclimation is linked to the photorespiration and N assimilation inhibition of plants exposed to elevated CO₂. The main goal of this study was to analyze the effect of interacting CO₂] and temperature on leaf photorespiration, C/N metabolism and N transport in wheat plants exposed to elevated CO₂] and temperature conditions. For this purpose, wheat plants were exposed to elevated CO₂] (400 vs 700 µmol mol^?1) and temperature (ambient vs ambient + 4°C) in CO₂ gradient greenhouses during the entire life cycle. Although at the agronomic level, elevated temperature had no effect on plant biomass, physiological analyses revealed that combined elevated CO₂] and temperature negatively affected photosynthetic performance. The limited energy levels resulting from the reduced respiratory and photorespiration rates of such plants were apparently inadequate to sustain nitrate reductase activity. Inhibited N assimilation was associated with a strong reduction in amino acid content, conditioned leaf soluble protein content and constrained leaf N status. Therefore, the plant response to elevated CO₂] and elevated temperature resulted in photosynthetic acclimation. The reduction in transpiration rates induced limitations in nutrient transport in leaves of plants exposed to elevated CO₂] and temperature, led to mineral depletion and therefore contributed to the inhibition of photosynthetic activity.