Abstract
Summary Methods using gas exchange measurements to estimate respiration in the light (day respiration Rd) make implicit assumptions about reassimilation of (photo)respired CO 2; however, this reassimilation depends on the positions of mitochondria.We used a reaction‐diffusion model without making these assumptions to analyse datasets on gas exchange, chlorophyll fluorescence and anatomy for tomato leaves. We investigated how Rd values obtained by the Kok and the Yin methods are affected by these assumptions and how those by the Laisk method are affected by the positions of mitochondria.The Kok method always underestimated Rd. Estimates of Rd by the Yin method and by the reaction‐diffusion model agreed only for nonphotorespiratory conditions. Both the Yin and Kok methods ignore reassimilation of (photo)respired CO 2, and thus underestimated Rd for photorespiratory conditions, but this was less so in the Yin than in the Kok method. Estimates by the Laisk method were affected by assumed positions of mitochondria. It did not work if mitochondria were in the cytosol between the plasmamembrane and the chloroplast envelope. However, mitochondria were found to be most likely between the tonoplast and chloroplasts.Our reaction‐diffusion model effectively estimates Rd, enlightens the dependence of Rd estimates on reassimilation and clarifies (dis)advantages of existing methods.
Highlights
Quantifying respiration is important for accurately predicting net ecosystem productivity, as respiratory losses can account for ≤ 40% of gross primary production (Gifford, 2003)
Unlike leaf respiration in the dark (Rdk), day respiration occurs simultaneously with photosynthetic CO2assimilation and is difficult to determine by gas-exchange measuring systems
Ci at the intersection point (CiÃ) is often used as the CO2 compensation point CÃ, at which the amount of CO2 produced by photorespiration equals the amount of CO2 consumed by ribulose biphosphate (RuBP) carboxylation
Summary
Quantifying respiration is important for accurately predicting net ecosystem productivity, as respiratory losses can account for ≤ 40% of gross primary production (Gifford, 2003). Methods exist to indirectly estimate Rd in C3 leaves from conventional gas-exchange measurements (Kok, 1948; Laisk, 1977; Brooks & Farquhar, 1985), sometimes combined with chlorophyll fluorescence measurements (Yin et al, 2009). The Laisk method (Laisk, 1977; Brooks & Farquhar, 1985) has become the most common one. It explores the linear part of several AN À Ci curves at low Ci concentrations (Ci is the intercellular CO2 partial pressure), measured at difference irradiances. The theoretical basis of the Laisk method is the FvCB model:
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