Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expanded leaves and whole plants of Amaranthus hypochondriacus L., Glycine max (L.) Merr., and Lycopersicon esculentum Mill. grown in controlled environments at 35 and 70 Pa carbon dioxide pressure were measured at 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant 24-h carbon dioxide exchange were used to determine relative growth rates, net assimilation rates, leaf area ratios, and the ratio of respiration to photosynthesis under the growth conditions. Biomass at a given time after planting was greater at the higher carbon dioxide pressure in G. max and L. esculentum, but not the C4 species, A. hypochondriacus. Relative growth rates for the same range of masses were not different between carbon dioxide treatments in the two C3 species, because higher net assimilation rates at the higher carbon dioxide pressure were offset by lower leaf area ratios. Whole plant carbon dioxide efflux rates per unit of mass were lower in plants grown and measured at the higher carbon dioxide pressure in both G. max and L. esculentum, and were also smaller in relation to daytime net carbon dioxide influx. Short-term responses of respiration rate to carbon dioxide pressure were found in all species, with carbon dioxide efflux rates of leaves and whole plants lower when measured at higher carbon dioxide pressure in almost all cases.