2.3 Photorespiration

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During gas exchange by illuminated leaves, photosynthesis and respiration sustain bidirectional fluxes of the same two gases. In light, the balance of CO2 and O2 exchange represents the activity of both processes and to detect and measure the rates of each requires that they be separated. Moreover, respiratory output of CO2 is also directly affected by light (Section 2.4), so that a further distinction needs to be made between ‘dark’ respiration during illumination, and ‘photorespiration’ per se. As outlined below, these processes are qualitatively distinct. Their separation necessitated some sophisticated measuring techniques, and their measurement led to some significant insights into leaf physiology.