The quantitative influence of enchytraeids (Oligochaeta) and microarthropods on decomposition of coniferous raw humus in microcosms

Material from the organic layer of a podsol soil in a spruce stand in southern Norway was incubated for 2 1/2 years at 15 degrees C in microcosms with a volume of 0.1 dm(3). The soil was sterilised and reinoculated with a mixed microflora before the incubation start, and given three different faunal communities: (1) A mixed assemblage of microarthropods plus the enchytraeid Cognettia sphagnetorum ("full fauna", FF), (2) only C. sphagnetorum ("enchytraeids", E), and (3) no animals added ("full fauna", NF). The respiration rare was measured during the last 14 months of incubation, and was highest in FF throughout this period. When all respiration analyses were pooled, the value for FF was 33 % higher than for NF and 25 % higher than for E. The substrate dry mass loss, measured twice, was also highest in FF (17 % higher in FF than in both the other treatments after 1 1/2 years of incubation, and 31 % higher than in both the other treatments after 2 1/2 years). Both for respiration and for mass loss, the difference between FF and the other two treatments was statistically significant, while there was no apparent difference between the E and NF treatments. There was no sign of a general rise or fall in the respiration rate during the 14 months from the first to the last analysis. The ammonium (and total N) concentration in the soil water was higher in FF and E than in NF. whereas the nitrate concentration was lowest in FF and highest in E. The higher mineralisation activity in the FF treatment was probably caused by the higher diversity of mesofauna, and perhaps also by higher diversities of microflora and microfauna accidentally introduced together with the arthropods.