Fungal and bacterial communities in Lumbricus terrestris burrow walls: a laboratory experiment

Abstract

The taxonomic composition of microbial communities in earthworm burrow walls was studied in a laboratory experiment lasting for 165 days. Anecic earthworms Lumbricus terrestris L. were kept in microcosms containing soil and litter from a lime (Tilia cordata) and beech (Fagus sylvatica) forest. Well-developed burrow linings consisting of earthworm faeces were formed in the “Tilia” treatment, but not in the “Fagus” treatment. The numbers and dominance structure of saprophytic bacteria were determined by the plate count method. Burrow walls in the “Tilia” treatment had tenfold higher CFU numbers than the control soil. The most abundant taxa were Cellulomonasand Promicromonospora, whereas Bacillus and Streptomyces dominated in the control soil. CFU numbers did not differ between burrow walls and control soil in the “Fagus” treatment, but the dominance of Bacillus was significantly decreased in burrow walls. The structure of fungal communities was analysed by modified washing and plating method. In both treatments the dominance structure of the fungal community in burrow walls differed from that in the control soil. The fungal community in burrow walls included many litter-associated taxa (Mucor hiemalis, Trichoderma koningii, Mortierella gamsii), but its taxonomic composition was soil-specific and depended on the quantity and quality of organic matter translocated down the soil profile. Mechanisms responsible for the formation of the specific burrow wall microflora are discussed. It is concluded that L. terrestris burrow walls contribute to the maintenance of high microbial diversity in mineral soil.