Apparent Reassimilation of Respiratory Carbon Dioxide by Different Plant Species

Abstract

Abstract Differences among species in respiration rates in CO 2 ‐free air, in light and dark, were studied using the standard leaf chamber technique and the infrared carbon dioxide analyzer. Photosynthesis, transpiration and respiration were measured. In all species studied, rates of respiration were considerably higher in dark than in light. This effect was assumed to be due to reassimilation of the respiratory CO 2 . A resistance analogy model was derived to account for the apparent differences in internal recycling of CO 2 among species; the differences were correlated with differences in maximum photosynthetic rates in normal air and optimal conditions (P 310 ) and with internal resistances to CO 2 diffusion (r k ). Species with high P 310 and low r k appear to reassimilate all the endogenous CO 2 , whereas other species with lower P 310 and higher r k appear to reassimilate only a part of their respiratory CO 2 . Experiments with the photosynthetic inhibitor, 3‐(3,4‐dichlorophcnyl)‐l,l‐dimethyl urea (DCMU), indicated that species with zero respiration in CO 2 ‐free air and light release respiratory CO 2 when photosynthesis is inhibited. It is concluded that the CO 2 released in the presence of DCMU represents respiratory CO 2 which recycles to photosynthesis under normal conditions.