MICROBIAL BIOMASS AND ACTIVITY IN CONTRASTING SOIL MATERIALS AFTER PASSAGE THROUGH THE GUT OF THE EARTHWORM LUMBRICUS-RUBELLUS HOFFMEISTER

Earthworms (Lumbricus rubellus) were fed on four different soils with light fraction organic material contents from 3.7 to 76.1% of the soil dry weight, and soil water potentials standardized at -8 kPa. Microbial biomass-C in the soils, as measured with a modified fumigation-extraction method, ranged from 0.4 to 7.5 mg C g-1 soil. After gut passage (6-8 h) microbial biomass-C was not changed significantly but rates of CO2 production, bacterial plate counts, moisture content and concentrations of soluble organic-C were higher in casts compared with the standardized soils ingested by the earthworms.