ENCHYTRAEID AND NEMATODE NUMBERS IN URBAN, POLLUTED SCOTS PINE (PINUS-SYLVESTRIS) STANDS IN RELATION TO OTHER SOIL BIOLOGICAL PARAMETERS

We examined the number of enchytraeids and nematodes in the mor humus layer of polluted Scots pine (Pinus sylvestris L.) stands, located on a sulphur gradient from 1.2 to 2.8 mg g-1 in mor humus and up to a dis tance of 40 km from the centre of Oulu, an industrialized city in nort hern Finland, in autumn 1989 and spring 1990. The number of enchytraei ds, dominated by one species, Cognettia sphagnetorum, showed a clear p ositive correlation with the soil respiration rate and the diversity a nd production of mycorrhizal fungi, and all these were negatively rela ted with S and N concentrations in the soil, as measured in 1987 and 1 988. This negative correlation may have been caused by an alteration i n food supply of enchytraeids, owing to changes in litter quality and the amount and species composition of fungi and mycorhizae. Nematode n umbers showed a positive correlation with the activity of dehydrogenas e enzymes, mineral N, and soil pH. The feeding characteristics of nema todes as a group need further study. The numbers of both enchytraeids and nematodes were higher in the autumn than in the spring, and in the case of nematodes this variation was related to soil moisture.