THE EFFECTS OF BACTERIVOROUS MITES AND AMEBAS ON MINERALIZATION IN A DETRITAL BASED BELOW-GROUND FOOD-WEB - MICROCOSM EXPERIMENT AND SIMULATION OF INTERACTIONS

The effects of two different bacterial grazers, an amoeba (Acanthamoeb a spec.) and an anoetid mite (Histiostoma litorale), separate and in c ombination, on C- and N mineralization were compared in a microcosm ex periment with sterilized silt loam soil, reinoculated with bacteria. L ucerne meal was added as substrate. The aim of the experiment was to s eparate the direct contribution of the mites to the mineralization fro m possible indirect effects, such as enhancement of microbial grazing by protozoa. The results showed a higher nitrogen mineralization in th e amoebae only treatment, compared to the mite treatment. From the com parison between the mite (BM) and the mite plus amoebae treatments (BM P), it could be concluded that the mite population had no measurable d irect or indirect effect on the nitrogen mineralization, even though t he N use efficiency of the mites was lower. No significant differences were found in the overall oxygen consumption, so no grazing effect on the microbial activity could be assessed. Model calculations showed t hat the low contribution of the mites to the nitrogen mineralization w as due to a lower production rate mites, compared to the protozoa. N e fficiency of the mites was lower than that of the amoebae. Bacterial p roduction in the protozoa treatments was 30 times the production in th e mite only treatment.