The influence of earthworms (Lumbricidae) on the nitrogen dynamics in the soil litter system of a deciduous forest

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Abstract
The influence of earthworms (Aporrectodea caliginosa (Savigny) and Lumbricus castaneus (Savigny)) on the rate of nitrogen net mineralization of the soil was studied in the laboratory and in the field. The additional mineralization of nitrogen cause by the burrowing activity of the substrat feeding earthworm A. caliginosa (N L )was directly correlated to the biomass of the lumbricids independently of their number. A rise in temperature caused an exponential increase in N L values. The Q 10 value of this process (2.18) was found to be much higher than that of the nitrogen mineralization without earthworms (Q 10=1.22). At 15°C the N L value caused by A. caliginosa was calculated to be about 250 μg N g-1 fresh body wt d-1. Using the experimentally determined exponential relationship between temperature and N L values, the additional nitrogen mineralization caused by a population of A. caliginosa in a beechwood on limestone was calculated to be 4.23 kg ha-1 a-1. In contrast to A. caliginosa the litter dwelling species L. castaneus lost considerable amounts of biomass (56%) during the 4 week incubation period. Only 1/3 of the nitrogen equivalent to the weight loss of the animals was recovered in the mineral nitrogen pool. The addition of litter (old beech leaf litter, freshly fallen beech and ash leaf litter) had a pronounced effect on both nitrogen net mineralization and N L values of the soil. Presence of old beech leaves caused an increase in both values, wheres the other litter types effected a decrease in nitrogen net mineralization. Fragmented ash litter was found to have the most distinct effect on N L values (-69%) and nitrogen net mineralization (-74%).