Contramensal interactions between two collembolan species: effects on population development and on soil processes

1, In the laboratory, a microcosm experiment was set up to study (1) the interaction between two collembolan species Onychiurus furcifer (Borner) and Heteromurus nitidus (Templeton) during 24 weeks of incubation; (2) the influence of slug (Arion rufus L.) cast material on the outcome of this interaction; and (3) the influence of collembolan activity on microbial biomass, respiration and nutrient mobilization. 2. The CO, production was monitored every other week and NH4+, NO3- and PO43- contents of leachates were determined every 4 weeks. After 12 and 2 1 weeks of incubation, the number of collembolans, basal respiration (O-2 consumption), microbial biomass (substrate-induced respiration method), specific respiration (qO(2)) and the content of NH4+, NO3- and PO43- in soil were determined. 3, Generally, the number of collembolans in microcosms with cast material exceeded that of microcosms without cast material considerably on average by factors of 20 and 26 for O. furcifer and H. nitidus, respectively. This increase was attributed to the additional food supply provided with the cast material. Numbers of collembolans declined during the experiment. 4. At both sampling dates, the presence of H. nitidus led to a reduction in the number of O, furcifer, whereas H, nitidus benefited from the presence of O, furcifer. Either trophic or non-trophic mechanisms, or both, may have caused this interaction (contramensalism, sensu Arthur & Mitchell 1989). 5. Both collembola species caused a decrease in microbial respiration, decomposition rates and tentatively also microbial biomass at high densities, whereas at low densities microbial respiration was stimulated while decomposition rates and microbial biomass remained unaffected. These effects were more pronounced for O.furcifer than for H, nitidus. 6, In treatments with cast material N-mobilization was increased by collembolan activity.