Comparison of the A-Cc curve fitting methods in determining maximum ribulose 1.5-bisphosphate carboxylase/oxygenase carboxylation rate, potential light saturated electron transport rate and leaf dark respiration.

A review of the literature revealed that a variety of methods are currently used for fitting net assimilation of CO(2)-chloroplastic CO(2) concentration (A-C(c)) curves, resulting in considerable differences in estimating the A-C(c) parameters [including maximum ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (V(cmax)), potential light saturated electron transport rate (J(max)), leaf dark respiration in the light (R(d)), mesophyll conductance (g(m)) and triose-phosphate utilization (TPU)]. In this paper, we examined the impacts of fitting methods on the estimations of V(cmax), J(max), TPU, R(d) and g(m) using grid search and non-linear fitting techniques. Our results suggested that the fitting methods significantly affected the predictions of Rubisco-limited (A(c)), ribulose 1,5-bisphosphate-limited (A(j)) and TPU-limited (A(p)) curves and leaf photosynthesis velocities because of the inconsistent estimate of V(cmax), J(max), TPU, R(d) and g(m), but they barely influenced the J(max) : V(cmax), V(cmax) : R(d) and J(max) : TPU ratio. In terms of fitting accuracy, simplicity of fitting procedures and sample size requirement, we recommend to combine grid search and non-linear techniques to directly and simultaneously fit V(cmax), J(max), TPU, R(d) and g(m) with the whole A-C(c) curve in contrast to the conventional method, which fits V(cmax), R(d) or g(m) first and then solves for V(cmax), J(max) and/or TPU with V(cmax), R(d) and/or g(m) held as constants.