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

Authors: Walker, Berkley; Ort, Donald

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2015
Publication Date: 6/15/2015
Citation: Walker, B.J., Ort, D.R. 2015. Improved method for measuring the apparent CO2 photocompensation point resolves the impact of multiple internal conductances to CO2 to net gas exchange. Plant Cell and Environment. 38:2462-2474.

Interpretive Summary: Biochemical models of leaf photosynthesis are important to understand how plants respond to current and future climate conditions. These models rely extensively on a parameter called the CO2 photocompensation point to determine how much carbon dioxide they will take from the atmosphere for growth and crop production. The CO2 photocompensation point has been measured in many previous studies and species, but it is not clear how much The CO2 photocompensation point differs or what might explain differences in past research. This work examines past measurements of the CO2 photocompensation point and suggests an optimal method to measure it. More accurate measurements of the CO2 photocompensation point will result in better models of photosynthesis and could possibly help determine strategies to improve crop photosynthesis.

Technical Abstract: There has been growing concern about methods used to measure the CO2 photocompensation point, a vital parameter to model leaf photosynthesis. the CO2 photocompensation point is often measured as the common intercept of several CO2 response curves, but this method may over-estimate the CO2 photocompensation point by using linear fits to extrapolate curvilinear responses and single conductance values to convert intercellular photocompensation points (Ci*) to chloroplastic the CO2 photocompensation point values. We used a combination of meta-analysis, original measurements, and modeled measurements to determine which factors impact estimates of the CO2 photocompensation point using the common intercept method. We found no correlation with CO2 measuring range in our meta-analysis but measured a significant effect in three species, suggesting that factors other than linear fits contributed to variation in literature values. Modeling of common intercept measurements indicated a large sensitivity to multiple conductances between the chloroplast and the intercellular airspace. These data lead us to suggest an optimal measuring regime and our meta-analysis suggests that the CO2 photocompensation point may acclimate to growth temperature.