Population dynamics of nematophagous fungi and nematodes in an arable soil: vertical and seasonal fluctuations

The population dynamics of nematophagous fungi and free-living nematodes were studied over a period of 2 y in an agricultural soil. Both the number of endoparasitic nematophagous fungi and the more parasitic nematode-trapping fungi declined. Nematode-trapping species regarded as good saprophytes did not decline, but were found in similar numbers throughout the study. At the same time both the total number of nematodes, as well as the number of the plant parasitic trichodorids decreased. The results indicate that there is a positive correlation between both the parasitic nematode-trapping species as well as the endoparasitic species and nematodes respectively, but not between the more saprophytic nematode-trapping species and nematodes. Nematophagous fungi were most common in the upper 30 cm soil layer while below 40 cm few were found. The most commonly-found nematode-trapping species was Arthrobotrys oligospora. The highest densities of nematode-trapping fungi, as well as the greatest number of species, were recorded in the autumn. In the upper soil layer the density of nematode-trapping fungi varied between 1.8 and 150 propagules g−1 soil. The mean number of nematode-trapping species recovered from 1.0 g of soil varied between 1.0 and 4.7 in the upper soil layer.