Fitting photosynthetic carbon dioxide response curves for C₃ leaves

Photosynthetic responses to carbon dioxide concentration can provide data on a number of important parameters related to leaf physiology. Methods for fitting a model to such data are briefly described. The method will fit the following parameters: V_cmax, J, TPU, R_d and g_m [maximum carboxylation rate allowed by ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco), rate of photosynthetic electron transport (based on NADPH requirement), triose phosphate use, day respiration and mesophyll conductance, respectively]. The method requires at least five data pairs of net CO₂ assimilation (A) and [CO₂] in the intercellular airspaces of the leaf (C_i) and requires users to indicate the presumed limiting factor. The output is (1) calculated CO ₂ partial pressure at the sites of carboxylation, C_c, (2) values for the five parameters at the measurement temperature and (3) values adjusted to 25°C to facilitate comparisons. Fitting this model is a way of exploring leaf level photosynthesis. However, interpreting leaf level photosynthesis in terms of underlying biochemistry and biophysics is subject to assumptions that hold to a greater or lesser degree, a major assumption being that all parts of the leaf are behaving in the same way at each instant.