Effects of mesofauna exclusion on the microbial biomass in two moder profiles

Summary

In December 1988, litterbags (mesh size 45 or 1000 μm) were exposed in the organic layer of a limed and unlimed moder soil under beech forest in the Solling area (Germany). At both sites, substrata from the L1, L2, F1, F2 and from the H Layer were sampled shortly before the beginning of the experiment, defaunated, filled separately into litterbags and replaced in the respective horizons in the field. Litterbags were retrieved on three sampling dates (May, September, and November 1989). The soil microbial biomass was estimated by means of the fumigation extraction method. The results show that the effects of excluding mesofauna from the 45-μm litterbags were different in different horizons, on different sampling dates and in different study sites. Calculation of the “average” effect from the three sampling dates revealed that mesofauna exclusion reduced the microbial biomass C at both sites. It was concluded from horizon- and season-specific differences between the two litterbag treatments that a depression in microbial biomass C in the organic layer of a moder soil by mesofaunal grazers is confined to situations where environmental conditions cause strong feeding pressure and when the microflora is exposed to environmental stress.