Regulation and Acclimation of C_2-photosynthesis in High CO_2

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The photosynthetic gas-exchange rates and their underlying biochemical properties were examined in young, fully expanded leaves of rice, wheat and pea. The plants were grown hydroponically under different CO_2 concentrations (35 Pa and 70 Pa). Enhanced CO_2 did not affect Rubisco content, carbonic anhydrase activity and electron transport capacity for a given leaf nitrogen content. However, it affected the light-saturated photosynthetic CO_2 response curve. The relative ratio of the initial slope to the CO_2-saturated photosynthesis decreased in the plants grown under high CO_2. This was mainly caused by an decrease in the initial slope for a given Rubisco content with rising CO_2 concentrations. This suggests that long-term CO_2 enhancement leads to an decrease in the CO_2 transfer conductance inside a leaf.