AUTOMATED MEASUREMENT OF THE RESPIRATORY RESPONSE OF SOIL MICROCOMPARTMENTS - ACTIVE MICROBIAL BIOMASS IN EARTHWORM FECES

A system to analyse the respiratory response of soil microcompartments by automated electrolytic microrespirometry is described. The system is computer controlled and allows simultaneous measurements of 16 samples. The minimum detection level is 0.83 mug O2 and the capacity of the system can be extended up to about 2500 mug O2 h-1. The frequency of measurements is optional and ranges from about 10 s to 1 h. The system was used to determine the active and total microbial biomass in soil and earthworm [Aporrectodea caliginosa (Savigny)] faecal particles (mean age of 4 days) by the O2 uptake method. Active microbial biomass was increased in earthworm faeces (+17%), but the percentages of active microorganisms were similar in faeces (5.0%) and soil (4.5%). Addition of diluted nutrients instead of dry matter resulted in very different shapes to O2 uptake curves, indicating damage to microorganisms due to sudden moisture alterations. The usefulness of the microrespirometer system to investigate microbial properties of soil microcompartments is discussed.