The calculated maximum net photosynthetic rate (P N ) at saturation irradiance (I m ) of 1 314.13 μmol m -2 s -1 was 25.49 μmol(CO 2 ) 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 P N 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 P N to I was nonlinear at low I for Oryza sativa, P N increased nonlinearly with I below saturation value. Above this value, P N decreased nonlinearly with I.

The model couples stomatal conductance (g s ) and net photosynthetic rate (P N ) describing not only part of the curve up to and including saturation irradiance (I max ), but also the range above the saturation irradiance. Maximum stomatal conductance (g smax ) and I max can be calculated by the coupled model. For winter wheat (Triticum aestivum) the fitted results showed that maximum P N (P max ) 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 CO 2 concentration because g smax 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 o C and 350 μmol mol −1 both P N and g s almost synchronously reached the maximum values at about 1 600 μmol m -2 s −1 . At 25 o C and 600 μmol mol −1 the I max corresponding to P max and g smax was 2 080 and 1 575 μmol m -2 s −1 , respectively.Additional key words: BWB model; irradiance; Triticum. --In the simulation of stomatal conductance (g s ), an empirical model for plant leaves by Ball et al. (1987), hereafter referred to as the BWB model, has been adopted widely in studies of ecological and physiological modelling. It has a solid experimental basis with a linear relationship between g s and net photosynthetic rate, P N (e.g. Ball et al. 1987, Di Marco et al. 1990