The role of substrate feeding earthworms (Lumbricidae) for bioturbation in a beechwood soil.

Burrow formation (burrow length and faeces production) of the substrate feeding earthworm Aporrectodea caliginosa (Savigny) in relation to three temperatures (5, 10 and 15°C) and soil moisture contents (48, 60 and 73% water of dry wt) was determined. Soil moisture content affected the burrowing activity of A. caliginosa only below a distinct threshold (60% water of dry wt). At sufficient moisture an, increase in temperature by 5° C approximately doubled the amount of egesta produced. Another substrate feeding earthworm (Octolasion lacteum (Örley)) showed a similar pattern of burrowing activity.The data for the dependence of the faeces production of A. caliginosa on soil temperature and moisture content were combined with field data. The amount of faeces produced by the population of this earthworm species in a beechwood on limestone was calculated to be about 4.23 kg ha-1 a-1. The amount of egesta produced by all substrate feeding species is assumed to exceed 6 kg ha-1 a-1, which is equivalent to a soil layer of approximately 9 mm. This group of earthworms is therefore considered to be of greater importance for bioturbation and the formation of mull than previously assumed.