Impacts of the epigeic earthworm Dendrobaena octaedra on microfungal community structure in pine forest floor: a mesocosm study

Abstract

In this mesocosm study, the effects of the invasion of the epigeic earthworm Dendrobaena octaedra on pine forest floor microfungi were studied. Intact pine forest floor cores were maintained in the laboratory at optimum (for microbial activity) moisture content and 15°C for 6 months. D. octaedra was added to half the cores at the equivalent of its 1993 field density of 250 immatures and 70 matures m −2. After 3 and 6 months, the cores were sampled for worm densities and microfungi. At both sampling times, some `control' cores contained worms and a gradient of worm densities from 0 to 736 m −2 was observed. Several fungal species were more abundant at intermediate worm densities. By 6 months, the number of fungal isolates had decreased in the worm treatment. It was suggested that: (i) in the absence of worm activity, competition between fungi limited the density of fungal species on litter and soil particles; (ii) at low levels of worm activity fungal competition was reduced, possibly through nutrient release and; (iii) at high levels of worm activity, fungal density decreased due to reduction in nutrient availability through the formation of organo–mineral complexes in casts. Fungal species which occur at lower frequencies in the worm treatment tended to be highly aggregated and those which were more abundant in the worm treatment were not aggregated, suggesting that microhabitat specialists were being adversely affected by the actions of D. octaedra.