SHORT-TERM AND LONG-TERM EFFECTS OF BACTERIVOROUS NEMATODES AND NEMATOPHAGOUS FUNGI ON CARBON AND NITROGEN MINERALIZATION IN MICROCOSMS

A microcosm experiment was carried out to quantify the effects of orga nisms at various trophic levels on C and N mineralization after the ad dition of crop residues to arable soil. The effects of the bacterivoro us nematodes Rhabditis sp. and Acrobeloides butschlii and of the nemat ophagous fungi Arthrobotrys oligospora und Drechmeria coniospora on so il respiration and N mineralization were measured over 6 months at 20- degrees-C. In the presence of nematodes, C mineralization was increase d during the first month and subsequently reduced; N mineralization wa s increased during the first 2 months and then reduced. The results su pport the assumption that nematodes influence C mineralization mainly indirectly by affecting bacterial activity, and N mineralization mainl y directly by mineralizing bacterial biomass. A. oligospora contribute d directly to C mineralization. The effect of both fungi on N minerali zation was indirect and resulted from the reduction in the numbers of nematodes. The results showed that the effects of nematodes and nemato phagous fungi and the mechanisms behind the effects may vary strongly in time, and are correlated with the type of organic matter decomposed .