The effects of earthworm functional diversity on microbial biomass and the microbial community level physiological profile of soils

A novel experiment design based on the axial simplex design was used to study the effects of earthworm functional diversity on microbial biomass and microbial community level physiological profiles in soils. This mesocosm experiment was carried out at two densities of earthworm and at two levels of food supply. Soil mesocosms were maintained for 7 months and watered each week with 300 ml of distilled water. At the end of this period the soil columns were divided into upper and lower halves and microbial biomass carbon and functional diversity assessed. Greater microbial biomass and activity was found in the upper layer of soil. Food supply was the major driver leading to increased microbial activity and biomass. Increased earthworm biomass had the opposite effect. In the lower soil layer, the presence of anecic worms had the greatest effect on microbial biomass and activity. This effect was enhanced with increased food supply. Overall, the relationship between earthworm functional diversity and microbial community level physiological profile appeared to be idiosyncratic and the effect of the earthworms varied with soil layer, initial biomass and food supply. The loss of any earthworm functional group might lead to significant alterations in the microbial biomass, distribution and physiological profile. (C) 2007 Elsevier Masson SAS. All rights reserved.