2015, DOI: 10.1111/pce.12562

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

Plant, Cell & Environment


Abstract

There is growing interest in accurate and comparable measurements of the CO2 photocompensation point (Γ*), a vital parameter to model leaf photosynthesis. The Γ* is measured as the common intercept of several CO2 response curves, but this method may incorrectly estimate Γ* by using linear fits to extrapolate curvilinear responses and single conductances to convert intercellular photocompensation points (Ci*) to chloroplastic Γ*. To determine the magnitude and minimize the impact of these artifacts on Γ* determinations we used a combination of meta-analysis, modeling, and original measurements to develop a framework to accurately determine Ci*. Our modeling indicated that the impact of using linear fits could be minimized based on the measurement CO2 range. We also propose a novel method of analyzing common intercept measurements using slope-intercept regression. Our modeling indicated that slope-intercept regression is a robust analytical tool that can help determine if a measurement is biased due to multiple internal conductances to CO2. Application of slope-intercept regression to Nicotiana tabacum and Glycine max revealed that multiple conductances likely have little impact to Ci* measurements in these species. These findings present a robust and easy to apply protocol to help resolve key questions concerning CO2 conductance through leaves.

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