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 mu molmol(-1)) and temperature (ambient vs ambient+4 degrees 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.