Influence of temperature on measurements of the CO2 compensation point: differences between the Laisk and O2-exchange methods

Abstract

The CO2 compensation point in the absence of day respiration (Γ*) is a key parameter for modelling leaf CO2 exchange. Γ* links the kinetics of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) with the stoichiometry of CO2 released per Rubisco oxygenation from photorespiration (α), two essential components of biochemical models of photosynthesis. There are two main gas-exchange methods for measuring Γ*: (i) the Laisk method, which requires estimates of mesophyll conductance to CO2 (g m) and (ii) measurements of O2 isotope exchange, which assume constant values of α and a fixed stoichiometry between O2 uptake and Rubisco oxygenation. In this study, the temperature response of Γ* measured using the Laisk and O2-exchange methods was compared under ambient (25 °C) and elevated (35 °C) temperatures to determine whether both methods yielded similar results. Previously published temperature responses of Γ* estimated with the Laisk and O2-exchange methods in Nicotiana tabacum demonstrated that the Laisk-derived model of Γ* was more sensitive to temperature compared with the O2-exchange model. Measurements in Arabidopsis thaliana indicated that the Laisk and O2-exchange methods produced similar Γ* at 25 °C; however, Γ* values from O2 exchange were lower at 35 °C compared with the Laisk method. Compared with a photorespiratory mutant (pmdh1pmdh2hpr) with increased α, wild-type (WT) plants had lower Laisk values of Γ* at 25 °C but were not significantly different at 35 °C. These differences between Laisk and O2 exchange values of Γ* at 35 °C could be explained by temperature sensitivity of α in WT and/or errors in the assumptions of O2 exchange. The differences between Γ* measured using the Laisk and O2-exchange method with temperature demonstrate that assumptions used to measure Γ*, and possibly the species-specific validity of these assumptions, need to be considered when modelling the temperature response of photosynthesis.

The space‐time continuum: the effects of elevated CO2 and temperature on trees and the importance of scaling

“…() used isotopic methods, and Griffin & Turnbull () used the Kok method. As differences in estimates of Γ * can be found under varied environmental conditions when using the Laisk technique or an O 2 isotope method (Walker & Cousins ), direct comparisons of the different techniques for measuring R light when CO 2 is varied may prove illuminating.…”

Improved method for measuring the apparent CO2 photocompensation point resolves the impact of multiple internal conductances to CO2 to net gas exchange

“…Currently the measured temperature response of Γ * or C i * determined from plants grown at a common temperature is used to model the temperature response of photosynthesis in climate change models (Bernacchi et al . , ; Walker & Cousins ; Walker et al . ).…”

Increased expression of mitochondria-localized carbonic anhydrase activity resulted in an increased biomass accumulation in Arabidopsis thaliana

“…The biochemical model for C3 photosynthesis (von Caemmerer 2000) was fitted on the data to yield an estimate for the carboxylation (Vcmax) and electron transport (Jmax) capacities. In the absence of mitochondrial respiration, the compensation point Γ * , was assumed to be 41.3 µmol mol −1 (Walker and Cousins 2013), and the effective Michaelis-Menten constant for Rubisco was 730 µmol mol −1 (von Caemmerer 2000). Respiration rates in the light were assumed to be equal to those in the dark.…”