The importance of species-specific and temperature-sensitive
parameterisation of A / C i models: a case study using cotton (
Gossypium hirsutum L.) and the automated ‘OptiFitACi’ R-package.
Abstract
Leaf gas exchange measurements provide an important tool for inferring a
plant’s photosynthetic biochemistry. In most cases, the responses of
photosynthetic CO 2 assimilation to variable
intercellular CO 2 concentrations ( A/
Ci response curves) are used to model the maximum
rate of carboxylation by ribulose-1,5-bisphosphate carboxylase/oxygenase
(Rubisco, V cmax) and the rate of electron
transport at a given photosynthetically active radiation (PAR; J
PAR). The standard Farquhar-Von Caemmerer-Berry model is
typically used with default parameters of Rubisco kinetic values and
mesophyll conductance to CO 2 ( g
m) derived from tobacco that impairs analytical
reliability across species. To study this, here we measured the
temperature responses of key in vitro Rubisco catalytic
properties and g m in cotton ( Gossypium
hirsutum cv. Sicot 71) and derived V cmax and
J 2000 ( J at 2000 µmol m
-2 s -1 PAR) from cotton A/
Ci curves incrementally measured at 15°C to 40°C
using cotton and tobacco parameters with our new automated fitting R
package ‘OptiFitACi’. When applied to cotton, the tobacco parameters
produced unrealistic J 2000: V
cmax ratio of <1 at 25°C, two- to three-fold
higher estimates of V cmax, approximately 50%
higher estimates of J 2000 and more variable
estimates of V cmax and J
2000, compared to model parameterisation with
cotton-derived values. We determined that errors arise when using a
g m of 0.23 mol m -2 s
-1 bar -1 or below and Rubisco CO
2-affinities under ambient O 2 (
K C 21%O2) outside 461 µbar to
627 µbar to model A/ C i responses in
cotton. We show how the multi- A/ C i
modelling capabilities of ‘OptiFitACi’ serves as a robust, user-friendly
extension of ‘plantecophys’ by providing simplified
temperature-sensitivity and species-specificity parameterisation
capabilities to enable higher accuracy estimates of V
cmax and J 2000.