Growth in elevated CO2 enhances temperature response of photosynthesis in wheat

The temperature dependence of C-3 photosynthesis may be altered by the growth environment. The effects of long-term growth in elevated CO2 on photosynthesis temperature response have been investigated in wheat (Triticum aestivum L.) grown in controlled chambers with 370 or 700 mu mol mol(-1) CO2 from sowing through to anthesis. Gas exchange was measured in flag leaves at ear emergence, and the parameters of a biochemical photosynthesis model were determined along with their temperature responses. Elevated CO2 slightly decreased the CO2 compensation point and increased the rate of respiration in the light and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) V-cmax, although the latter effect was reversed at 15 degrees C. With elevated CO2, J(max) decreased in the 15-25 degrees C temperature range and increased at 30 and 35 degrees C. The temperature response (activation energy) of V-cmax and J(max) increased with growth in elevated CO2. CO2 enrichment decreased the ribulose 1,5-bisphosphate (RuBP)-limited photosynthesis rates at lower temperatures and increased Rubisco- and RuBP-limited rates at higher temperatures. The results show that the photosynthesis temperature response is enhanced by growth in elevated CO2. We conclude that if temperature acclimation and factors such as nutrients or water availability do not modify or negate this enhancement, the effects of future increases in air CO2 on photosynthetic electron transport and Rubisco kinetics may improve the photosynthetic response of wheat to global warming.