REDUCTION OF RESPIRATION BY HIGH AMBIENT CO2 AND THE RESULTING ERROR IN MEASUREMENTS OF RESPIRATION MADE WITH O2 ELECTRODES

Respiration rates of Lenina gibba fronds and Orobanche aegyptiaca and Lactuca saliva seedlings, were measured with a Clark type oxygen electrode in the presence or absence of a carbon-dioxide absorber (KOH) in the gas phase. Measured respiration rates in the presence of KOH were 17-34% higher than in its absence. The suppression of respiration by high CO2concentrations, [CO2], was confirmed by parallel studies of CO2efflux, made by infrared gas spectrometry. These results are consistent with other reports of reduced rates of respiration at high [CO2]. Measurements of respiration quotients of Lemna and Lactuca were made at 0 and 100 Pa [CO2]. Results did not support the possibility of induced dark fixation of CO2at the ambient atmospheric [CO2] predicted for the next century (35-100 Pa). It is concluded that the numerous reports of respiration measurements made with O2electrodes, in the absence of a CO2absorber, may contain a significant error. © 1993 Annals of Botany Company.