Influence of temperature on measurements of the CO 2 compensation point: differences between the Laisk and O 2 -exchange methods

Author： Walker Berkley J. Cousins Asaph B.

Publisher： Oxford University Press

ISSN： 1460-2431

Source： Journal of Experimental Botany, Vol.64, Iss.7, 2013-04, pp. : 1893-1905

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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.