The model couples stomatal conductance (gs) and net photosynthetic rate (PN) describing not only part of the curve up to and including saturation irradiance (Imax), but also the range above the saturation irradiance. Maximum stomatal conductance (gsmax) and Imax can be calculated by the coupled model. For winter wheat (Triticum aestivum) the fitted results showed that maximum PN
(Pmax) at 600 µmol mol-1 was more than at 350 µmol mol-1 under the same leaf temperature, which can not be explained by the stomatal closure at high CO2 concentration because gsmax at 600 µmol mol-1 was less than at 350 µmol mol-1. The irradiance-response curves for winter wheat had similar tendency, e.g. at 25 °C and 350 µmol mol-1 both PN and gs almost synchronously reached the maximum values at about 1 600 µmol m-2 s-1. At 25 °C and 600 µmol mol-1 the Imax corresponding to Pmax and
gsmax was 2 080 and 1 575 µmol m-2 s-1, respectively. and Z.-P. Ye, Q. Yu.
The calculated maximum net photosynthetic rate (PN) at saturation irradiance (I m) of 1 314.13 µmol m-2 s-1 was 25.49 µmol(CO2) m-2 s-1, and intrinsic quantum yield at zero irradiance was 0.103. The results fitted by nonrectangular hyperbolic model, rectangular hyperbolic method, binomial regression method, and the new model were compared. The maximum PN values calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were higher than the measured values, and the I m calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were less than measured values. Results fitted by new model showed that the response curve of PN to I was nonlinear at low I for Oryza sativa, PN increased nonlinearly with I below saturation value. Above this value, PN decreased nonlinearly with I.