MICROBIAL CARBON TURNOVER IN BEECH FOREST SOILS WORKED BY APORRECTODEA-CALIGINOSA (SAVIGNY) (OLIGOCHAETA, LUMBRICIDAE)

Effects of the endogenic earthworm species Aporrectodea caliginosa (Savigny) on the edaphic microflora were studied in six German beech forest soils using the fumigation-extraction method. The following response variables were measured: biomass (C(mic)), C incorporation from C-14-labelled beech leaf litter (C-14mic) and two metabolic quotients (qCO2: mu-g CO2-C-mu-g-1 C(mic) h-1; (qCO2)-C-14: mu (CO2)C-14-C-mu-g-1 C-14mic h-1). After removing the earthworms from the experimental containers at day 21, the experiment ran for a further 21 days to study the long-term alteration of microbial performance in earthworm worked soils. At day 21, C(mic) and C-14mic were reduced in the earthworm treatments of five soils and qCO2 and (qCO2)-C-14 were increased in all soils. Effects on C(mic) and C-14mic were not correlated to each other. The day 21 effects of A. caliginosa on C(mic) and qCO2 declined, while the stimulation of (qCO2)-C-14 increased with increasing soil acidity. Day 42 measurements showed that the long-term effects of A. caliginosa on microbial C use were highly soil specific and were opposite to the effects measured at day 21 in most of the soils. It is concluded from these results that A. caliginosa alters the biomass and the metabolic activity of the edaphic microflora over a wide range of soils, that these alterations are highly soil and resource specific and that the microbial C turnover in soils freshly worked by A. caliginosa is significantly different from the microbial C turnover in aged casts and burrows.