EFFECTS OF FUNGIVOROUS AND PREDATORY ARTHROPODS ON NEMATODES AND TARDIGRADES IN MICROCOSMS WITH CONIFEROUS FOREST SOIL

Effects of fungivorous and predatory soil arthropods on free-living ne matodes and tardigrades were studied in a factorial microcosm experime nt. A stepwise increase in faunal complexity was obtained by adding so il arthropods to defaunated humus samples from an irrigated + fertiliz ed and an untreated stand of Scots pine. The effects were assessed aft er 103 and 201 days at 15 degrees C and a soil moisture content of 50% water-holding capacity. The study showed that a diverse community of ''fungivorous'' arthropods (collembola and oribatid mites), present in numbers similar to those in the field, reduced the abundance of nemat odes. A complete community of fungivorous and predatory arthropods (e. g., gamasides, spiders, and cantharid larvae) further strengthened thi s repressive effect. Certain nematode genera were more affected than o thers. Tardigrades seemed to be efficient predators on nematodes, but their numbers were, in turn, strongly reduced by predatory arthropods. Because predatory arthropods fed on both nematodes and their tardigra de predators, the impact of arthropod predators on nematode regulation was greater than it appeared to be on the basis of nematode numbers. Humus type also interacted with the other factors. Nematode numbers we re initially higher in the untreated humus than in the irrigated + fer tilized humus. However, because tardigrade populations increased only in the untreated humus, nematode numbers decreased more in this humus than in the irrigated + fertilized humus. The study demonstrates that nematode abundance can be regulated by a number of types of interactin g predators.