The light compensation point (I) is the light intensity on the light curve where the rate of photosynthesis exactly matches the rate of cellular respiration. At this point, the uptake of CO through photosynthetic pathways is equal to the respiratory release of carbon dioxide, and the uptake of O by respiration is equal to the photosynthetic release of oxygen. The concept of compensation points in general may be applied to other photosynthetic variables, the most important being that of CO concentration &ndash; CO compensation point (Γ).Interval of time in day time when light intensity is low due to which net gaseous exchange is zero is called as compensation point.
In assimilation terms, at the compensation point, the net carbon dioxide assimilation is zero. Leaves release CO by photorespiration and cellular respiration, but CO is also converted into carbohydrate by photosynthesis. Assimilation is therefore the difference in the rate of these processes. At a given partial pressure of CO (0.343 hPa in 1980 atmosphere), there is an irradiation at which the net assimilation of CO is zero. For instance, in the early morning and late evenings, the light compensation point I may be reached as photosynthetic activity decreases and respiration increases. The concentration of CO also affects the rates of photosynthesis and photorespiration. Higher CO concentrations favour photosynthesis whereas low CO concentrations favor photorespiration, producing a CO compensation point Γ for a given irradiation.