Discussion on the Kok Effect and its utility for respiration in the light

In the past 6 months, two papers have been published discussing nuances of the "Kok method", which uses measurements of high resolution low-light curves to detect the degree of inhibition of respiration by light. I have worked extensively with this method for my graduate research in the Arctic, and more recently in deciduous hardwood canopy species at Harvard Forest. 

The first paper, by Farquhar and Busch approaches the method with concern that the acceleration of the quantum yield at very low lights is controlled by the change in chloroplastic CO2 concentration, and not a signal of a relaxation of inhibition at low light.

In response to these claims, a paper by Buckley, Vice, and Adams, applied the Kok method in young and old leaves under two measurement O2 concentrations, and used this data for evidence to oppose the claims made by Farquhar and Busch. Primarily, Buckley, Vice, and Adams show that the breakpoint and the acceleration of quantum yield at low light cannot be explained fully by just changes in chloroplastic CO2 concentrations, but rather is tied to respiration. However, the note the importance of accounting for cc when using this method, and voice concern about it's broad application. 

These papers follow a vigorous discussion about respiration in the light that has resulted in two more recent publications led by Guillaume Tcherkez in New Phytologist: one describing the workshop last summer in Angers, France (that I am grateful to have attended), and another that reviews the state of respiration in the light using multiple approaches. 

This active (and all polite and open-minded!) exchange of ideas in New Phytologist promotes the ongoing challenge of how to deal with respiration in the light in leaves, and also in whole canopies. The application of the inhibition in models can have large consequences for how we think about carbon exchange at different scales.