Biochemical model of C 3 photosynthesis applied to wheat at different temperatures

We examined the effects of leaf temperature on the estimation of maximal Rubisco capacity ( V cmax ) from gas exchange measurements of wheat leaves using a C 3 photosynthesis model. Cultivars of spring wheat ( Triticum aestivum (L)) and triticale ( X Triticosecale Wittmack) were grown in a greenhouse or in the field and measured at a range of temperatures under controlled conditions in a growth cabinet (2 and 21% O 2 ) or in the field using natural diurnal variation in temperature, respectively. Published Rubisco kinetic constants for tobacco did not describe the observed CO 2 response curves well as temperature varied. By assuming values for the Rubisco Michaelis–Menten constants for CO 2 ( K c ) and O 2 ( K o ) at 25 °C derived from tobacco and the activation energies of V cmax from wheat and respiration in the light, R d , from tobacco, we derived activation energies for K c and K o (93.7 and 33.6 kJ mol −1 , respectively) that considerably improved the fit of the model to observed data. We confirmed that temperature dependence of dark respiration for wheat was well described by the activation energy for R d from tobacco. The new parameters improved the estimation of V cmax under field conditions, where temperatures increased through the day.