FLOW MICROCALORIMETRY MEASUREMENTS OF AEROBIC AND ANAEROBIC SOIL MICROBIAL ACTIVITY

Heat output can be used as an indicator of microbial activity and is u sually measured in a microcalorimeter with closed ampoules. In long-te rm experiments particularly, interpretation of the data is hindered by the changing environment in the closed ampoules because of O-2 consum ption and CO2 enrichment. We used a combination of a flow-microcalorim eter and a gas chromatograph to measure the heat flux and CO2 and N2O production rates under controlled conditions. Simultaneous detection o f the heat output and CO2 emission allowed calculation of the calorime tric:CO2 (Cal/CO2) ratio. A mean ratio of -435 kJ mol(-1) CO2 was dete cted in six different soils amended with glucose and incubated under a erobic conditions. This ratio indicated that CO2 was the end-product o f catabolism. In wet 10-12 mm soil aggregates of a gleyic vertisol ame nded with glucose, values of -285 kJ mol(-1) CO2 under an aerobic and -141 kJ mol(-1) CO2 under a N-2 atmosphere was determined. These findi ngs indicated that fermentative metabolism occurred. The Cal/CO2 ratio was not affected when enough NO3- was available and denitrification p rocesses (N2O production) were possible.