Photosynthesis-stomatal conductance model LEAFC3-N: specification for barley, generalised nitrogen relations, and...

We discuss a generalised formulation of the nitrogen-sensitive photosynthesis-stomatal conductance model LEAFC3-N to be used as a submodel of functional-structural plant models (FSPMs) or traditional crop growth models for C₃-crops. Based on a parameterisation study for barley, we demonstrate that the large variation of characteristics related to potential leaf photosynthesis and stomatal conductance, along with different factors, can be accounted for by introducing functions that relate parameter values to nitrogen contents. These relationships follow the same pattern for different C₃ crops, and their parameters are in close range. The accuracy of the parameters and the minimum simulation time step required for reliable predictions of the integrated diurnal carbon gain (IDC) is assessed. For IDC predictions with an accuracy of about ±5%, the accuracy of the slope of the relationship between maximum carboxylation rate and leaf nitrogen content should be of similar order. For other key model parameters, an error of ±20% or even greater may be tolerated. A time step of 1-2 h will be sufficient to predict IDC with an accuracy of about ±5%.