Fitting photosynthetic carbon dioxide response curves for C₃ leaves

TLDR

Photosynthetic responses to CO₂ concentration yield key leaf physiological parameters, but interpreting them relies on the assumption that all leaf parts behave uniformly at each instant. The study aims to fit a photosynthetic model to CO₂ response data to explore leaf‑level photosynthesis. The method fits Vcmax, J, TPU, Rd, and gm using at least five net CO₂ assimilation–intercellular CO₂ data pairs, with the user specifying the presumed limiting factor. The output provides the calculated CO₂ partial pressure at carboxylation sites, the five fitted parameters at measurement temperature, and temperature‑adjusted values at 25 °C for comparison.

Abstract

ABSTRACT 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 CO 2 assimilation ( A ) and [CO 2 ] 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.