Leaf litter fragmentation by the earthworm Lumbricus terrestris L.

Earthworms play an important role in the mechanical comminution of leaf lit ter, but experimental evidence and quantitative data are scarce. We studied the extent of litter fragmentation in the digestive tract of Lumbricus ter restris L. and the role of mineral particles in this process. Adult anecic earthworms L. terrestris were placed into the mixture of lime (Tilia cordat a) leaf litter and riverbank sand (1:1 by weight). After five days earthwor ms were transferred into the pure litter. The quantity and size of the sand grains in earthworm gizzards and casts, and the size of litter fragments i n the casts were measured one, two, three, five and eight days after the tr ansfer into the pure litter. Earthworms actively selected sand from the mix ture of litter and sand and showed evident preference for sand particles of small size (0.5-1 mm) over larger (1-2 mm and 2-3 mm) sand grains. Average content of sand in earthworm casts initially was 78 % (by weight) and grad ually decreased to 2-4 % when earthworms were maintained in the pure litter . At the same time, the mean size of litter fragments in the casts increase d from 0.035 mm(2) on the first day to 0.232 mm(2) on the eighth day. When the sand was available, a majority (68 %) of litter fragments in L. terrest ris casts had a size less than 0.001 mm(2), with a median size of 0.46 . 10 (-3) mm(2). The mean and median fragment size and the quantity of sand in t he casts were strongly negatively correlated (r = -0.802 and -0.844 respect ively).