The Monomolecular and Rectangular Hyperbola as Empirical Models of the Response of Photosynthetic Rate to Photon Flux Density, with Applications to Three Veronica Species

The properties of the rectangular hyperbola and monomolecularfunctions, with respect to the photosynthesis/photon flux density(PFD) relationship, are discussed, and the shortcomings of theformer are highlighted. Both models were fitted to data acquiredfrom three closely related Veronica species of contrasting ecology.The non-linear regression algorithms give estimates, with standarderrors, of light saturated photosynthetic rate, light compensationpoint, dark respiration rate, and photochemical efficiency atlow PFD. While the rectangular hyperbola gave almost as gooda fit to the data as the monomolecular for each species, thelight saturated photosynthetic rate estimate given by the formerwas always unacceptably high in comparison with that indicatedby the obvious trend of the data. Moreover, this tendency wasaccentuated if near-saturating PFDs were removed from data sets,and there was a tendency for the fitting algorithm to becomeunstable. No such problems were encountered with the monomolecularfunction, and it is suggested that this be used whenever a simpleempirical model is required to analyze photosynthesis/PFD data. Veronica montana L, Veronica chamaedrys L, Veronica officinalis L, wood speedwell, Germander speedwell, common speedwell, empirical mathematical model, monomolecular function, rectangular hyperbola function, nonlinear regression, photosynthesis, photon flux density, light saturated photosynthetic rate, light compensation point, photochemical efficiency, dark respiration rate