Reduction of respiration by high ambient co₂and the resulting error in measurements of respiration made with o₂electrodes

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.