Application to wheat and barley of two leaf photosynthesis models for C 3 plants

Two models describing the relationship between net photosynthesis of leaves of C 3 plants, light intensity and CO 2 concentration in the substomatal cavities are described and fitted to data obtained in a constant environment cabinet and in the field. The first model, based on a resistance analogue for gaseous diffusion and Michaelis‐Menten biochemistry, gave the best fit to the data. For the field data, four parameters were required–quantum yield, mesophyll resistance, ‘dayrsquo; respiration and a photorespiration constant. For the cabinet data, a parameter representing the limiting photosynthesis rate was required. The second model, based on a recent more rigorous biochemical analysis of photosynthesis, contains five parameters–quantum yield, maximum carboxylation rate, ‘day’ respiration, a photorespiration constant and a maximum electron transport rate. It fitted the data less well.