LEAFC3-N: a nitrogen-sensitive extension of the CO2 and H2O gas exchange model LEAFC3 parameterised and tested for winter wheat (Triticum aestivum L.)

The generic steady-state flux model 'LEAFC3' [Nikolov, N.T., Massman, W.J., Schoettle, A.W., 1995. Coupling biochemical and biophysical processes at the leaf level: an equilibrium photosynthesis model for leaves of C-3 plants. Ecol. Model. 80, 205-235], that couples major processes of CO2 and H2O gas exchange with stomatal function and the energy and mass transfer in the leaf-boundary layer was extended to account for effects of leaf nitrogen content. Relationships between nitrogen mass per unit leaf area, Na, and key model parameters were derived from field measurements of CO2 exchange rate (A) and transpiration rate (E) carried out on leaves of winter wheat at different stages of development. Maximum carboxylation rate Vc,max, maximum quantum yield of photosynthetic electron transport, φa, and the ratio of mitochondrial respiration Rdark to Vc,max, Cdr, were correlated linearly with Na. The parameter m that determines the composite sensitivity of leaf stomatal conductance gs to net photosynthesis rate, air humidity, and ambient CO2 concentration, showed a non-linear decline with increasing Na. The maximum rate of electron transport, Jmax, was assumed proportional to Vc,max and hence only indirectly related to Na. The proposed nitrogen-sensitive LEAFC3-N model was validated based on an independent set of data obtained from diurnal time course measurements of A and E. Although the parameterisation of the model has to be verified with more data from different growth conditions, the model can be used as a submodel in modelling plant and canopy-scale gas exchange of winter wheat.