The applied science of crop production analyses of plant growth, plant development, and formation of yield from an integrative point of view. Mathematical models thereby are used as tools for a detailed and mechanistic system description. Since the 1980ies, photosynthesis models describing gas and radiation exchange of plant organs have been developed based on the work of Farquhar et al. (1980) and Ball et al. (1987). Among them, the nitrogen sensitive extension LEAFC3-N (Müller et al., 2005) of the model LEAFC3 from Nikolov et al. (1995) represents a rather complex and improved photosynthesis model, which describes the CO2 and H2O gas exchange in relation to the input variables radiation, temperature, CO2 and O2 concentration of the air, humidity of the air, and nitrogen content of the leaf. The main focus of this thesis is to test the universality of the mechanistic model concept regarding the stability of parameters. To this end, gas exchange measurements of spring barley (Hordeum vulgare L., cv. 'Barke') were made in two climate chamber and two field experiments. Using these data, photosynthetic characteristics such as the maximum carboxylation rate Vcmax were estimated. Hence, we derived parameters of nitrogen and temperature dependencies of model characteristics. The results obtained from the experiments show that the amount of nitrogen fertilisation did not significantly affect the model parameters. However, growth temperature has a significant impact on some parameters of the functions describing the nitrogen and temperature dependencies of Vcmax and other characteristics. These modulations of the model parameters describe the physiological adaptation of the plants to growth temperature conditions. The model was validated based on measurements of diurnal time courses of net photosynthesis rate An, transpiration rate E, and stomatal conductance gs. Measured time courses of An, E, and gs could be simulated fairly well especially in the morning hours with the parameterisation used. The difference between measured and calculated values which is related to drought stress conditions thereby could be explained by including functions accounting for the effect of leaf water potential Ψ on gs, Vcmax, and Jmax.