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Appl Environ Microbiol. 1970 January; 19(1): 32-38
Copyright © 1970 American Society for Microbiology. All Rights Reserved.

Measurement of ¹⁴CO₂ Assimilation in Soils: an Experiment for the Biological Exploration of Mars

Bioscience Section, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91103

ABSTRACT

A method is described for the measurement of ¹⁴CO₂ assimilation by microorganisms in soils. A determination involves exposing soil to ¹⁴CO₂, pyrolyzing the exposed soil, trapping the organic pyrolysis products on a column of firebrick coated with CuO, combusting the trapped organics by heating, and measuring the radioactivity in the CO₂ produced in the combustion. The detection of significant levels of ¹⁴C in the trapped organic fraction appears to be an unambiguous indication of biological activity. The ¹⁴CO₂ which is adsorbed or exchanged into soils by nonbiological processes does not interfere. The method easily detects the ¹⁴CO₂ fixed by 10² to 10³ algae after light exposure for 3 to 24 hr. Assimilation of ¹⁴C is also demonstrable in dark-exposed soils containing 10⁵ to 10⁶ heterotrophic bacteria. Possible applications of the method in the biological exploration of Mars are discussed.

¹ Present address: University of Southern California, School of Medicine, Department of Pharmacology, Los Angeles, Calif.