Applicability of radiotracer methods of measuring(14)CO 2 assimilation for determining microbial activity in soil including a newin situ method.

The applicability of two methods (pyrolysis gas chromatography and acidification-wet oxidation) for determining(14)CO2 incorporation into soil microorganisms was investigated. Both methods were able to distinguish biologically incorporated(14)C from abiotically adsorbed(14)C, but to varying degrees, there being a larger carryover of abiotic(14)C into the organic fraction and a higher percentage of assimilated(14)C in the organic fraction with the wet oxidation method. Using(14)C assimilation as a measure, it was possible to determine microbial activities in soils of diverse properties under a variety of conditions, including polar soils under harsh environmental conditions. Both light and dark(14)CO2 fixation was measurable.(14)CO2 assimilation was not always proportional to the enumerable microorganisms. A new design for measurement of microbial activityin situ enabled measurement of total C influx (primary productivity) into soils with minimal perturbation to the natural soil ecosystem.