Estimating leaf day respiration from conventional gas exchange measurements

Leaf day respiration (R_d) strongly influences carbon-use efficiencies of whole plants and the global terrestrial biosphere. It has long been thought that R_d is slower than respiration in the dark at a given temperature, but measuring R_d by gas exchange remains a challenge because leaves in the light are also photosynthesizing. The Kok method and the Laisk method are widely used to estimate R_d. We highlight theoretical limitations of these popular methods, and recent progress toward their improvement by using additional information from chlorophyll fluorescence and by accounting for the photosynthetic reassimilation of respired CO₂. The latest evidence for daytime CO₂ and energy release from the oxidative pentose phosphate pathway in chloroplasts appears to be important to understanding R_d.