Technique for Measuring 14 CO 2 Uptake by Soil Microorganisms In Situ

Uptake of14 CO2 in soils due to algae or sulfur-oxidizing bacteria was examined by incubation of soil samples with gaseous14 CO2 and subsequent chemical oxidation of biologically fixed radioactive isotope to14 CO2 for detection with a liquid scintillation counting system. The14 CO2 was added to the soil in the gas phase so that no alteration of the moisture or ionic strength of the soil occurred. Wet oxidation of radioactive organic matter was carried out in sealed ampoules, and the14 CO2 produced was transferred to a phenethylamine-liquid scintillation counting system with a simply constructed apparatus. The technique is inexpensive and efficient and does not require elaborate traps since several possible interfering factors were found to have no harmful effects. Experiments in coal mine regions and in geothermal habitats have demonstrated the ecological applicability of this technique for measurement of CO2 fixation by sulfur-oxidizing bacteria and soil algae.