The impact of light inhibition of leaf respiration on net photosynthesis

Abstract

In addition to being a vital component of plant metabolism, leaf respiration (R, non-photorespiratory mitochondrial CO2 release) also represents a major source of CO2 release in plants. While leaf respiration occurs both in the light and in darkness, the extent to which it continues in darkness is highly variable. Most studies have reported that the rate of leaf respiration in the light is less than that in darkness with the degree of inhibition varying from 0 to 90%. The inhibition of R by light is rapid (less than 50 s) and occurs at low irradiance. This presentation will discuss possible mechanisms responsible for light inhibition of leaf respiration and the impact of light inhibition on net photosynthetic CO2 uptake. The effect of short- and long-term changes in temperature on light inhibition of leaf respiration will be highlighted. Our results demonstrate that the degree of light inhibition of leaf respiration is similar in warm and cold-grown plants. Regardless of species or growth temperature, light reduces the short-term temperature sensitivity of leaf respiration; little or no light inhibition occurs in the cold, whereas very high degrees of inhibition occur in leaves exposed to high temperatures (e.g. 30°C). One consequence is that at high temperatures light reduces the proportion of gross CO2 uptake released back into the atmosphere by leaf respiration by approximately 80%, compared to if light did not inhibit leaf respiration. The impacts of this reduction on daily net carbon gain will be discussed.