Figure 4.

Assimilation-weighted sensitivity to CO₂ (vertical axis) and O₂ (horizontal axis) as affected by increasing light levels. At limiting light levels, the energy cost of photorespiration results in a reduction in CO₂ assimilation capacity. As light levels increase, the upper bound becomes sensitive to end-product synthesis. Photorespiration stimulates CO₂ assimilation by adding end-product synthesis capacity in the form of serine export. Redrawn from Sharkey (1990). Arrows indicate the response of photosynthesis to the indicated gases.