Flow-microcalorimetry measurements of aerobic and anaerobic soil microbial activity

摘要

Heat output can be used as an indicator of microbial activity and is usually measured in a microcalorimeter with closed ampoules. In long-term experiments particularly, interpretation of the data is hindered by the changing environment in the closed ampoules because of O2consumption and CO2enrichment. We used a combination of a flow-microcalorimeter and a gas chromatograph to measure the heat flux and CO2and N2O production rates under controlled conditions. Simultaneous detection of the heat output and CO2emission allowed calculation of the calorimetric: CO2(Cal/CO2) ratio. A mean ratio of-435 kJ mol-1CO2was detected in six different soils amended with glucose and incubated under aerobic conditions. This ratio indicated that CO2was the end-product of catabolism. In wet 10–12 mm soil aggregates of a gleyic vertisol amended with glucose, values of-285 kJ mol-1CO2under an aerobic and-141 kJ mol-1CO2under a N2atmosphere was determined. These findings indicated that fermentative metabolism occurred. The Cal/CO2ratio was not affected when enough NOinf3sup-was available and denitrification processes (N2O production) were possibl