Photosynthetic refixing of CO2 is responsible for the apparent disparity between mitochondrial respiration in the light and in the dark

The net photosynthetic rate (P (N)), the sample room CO2 concentration (CO2S) and the intercellular CO2 concentration (C (i)) in response to PAR, of C-3 (wheat and bean) and C-4 (maize and three-colored amaranth) plants were measured. Results showed that photorespiration (R (p)) of wheat and bean could not occur at 2 % O-2. At 2 % O-2 and 0 mu mol mol(-1) CO2, P (N) can be used to estimate the rate of mitochondrial respiration in the light (R (d)). The R (d) decreased with increasing PAR, and ranged between 3.20 and 2.09 mu mol CO2 m(-2) s(-1) in wheat. The trend was similar for bean (between 2.95 and 1.70 mu mol CO2 m(-2) s(-1)), maize (between 2.27 and 0.62 mu mol CO2 m(-2) s(-1)) and three-colored amaranth (between 1.37 and 0.49 mu mol CO2 m(-2) s(-1)). The widely observed phenomenon of R (d) being lower than R (n) can be attributed to refixation, rather than light inhibition. For all plants tested, CO2 recovery rates increased with increasing light intensity from 32 to 55 % (wheat), 29 to 59 % (bean), 54 to 87 % (maize) and 72 to 90 % (three-colored amaranth) at 50 and 2,000 mu mol m(-2) s(-1), respectively.