DYNAMICS AND STRATIFICATION OF FUNCTIONAL-GROUPS OF NEMATODES IN THE ORGANIC LAYER OF A SCOTS PINE FOREST IN RELATION TO TEMPERATURE AND MOISTURE

Nematode trophic groups were studied in litterbags in a Pinus silvestr is forest using sampling periods of 8 weeks during 2.5 years. Temperat ure, moisture relationships and annual periodicity of nematodes were a nalyzed in the litter (L), fragmentation (F) and humus (H) horizons. L itterbags containing L, F and Il material were placed in stacks and bu ried in the organic layer. Undisturbed core samples were used to compa re the nematode abundance under normal field conditions with that in t he litterbags. Time dependence of population growth and colonization w as also studied in separate litterbags that were replaced every 8 week s. During the first 4 to 6 months of the experiment, nematodes in the litterbag stacks grew rapidly to circa 5 x 10(6) m(-2). After that per iod, abundance gradually decreased to about 2.5 x 10(6) m(-2). These a bundances were similar to those found in undisturbed cores. Nematode a bundance during the first year was most pronounced in the top (L) litt erbags; subsequently densities were more or less the same in the three organic horizons, reflecting the gradual change of L to F material. O n average, during 2.5 years, bacterial feeding nematodes were the domi nant group in the organic horizons (73%), with 17% hyphal feeders and 9% plant feeders. There were dissimilarities between layers and in the course of time. The number of hyphal feeding nematodes differed signi ficantly between layers. In the first 2 to 4 months, hyphal feeding ne matodes equalled the bacterial feeders in the L layer. Later bacterial feeders became dominant. The highest number of plant feeding nematode s was found in the F litterbags. Significant effects of temperature an d moisture were mainly found on bacterial feeding nematodes. Regressio n coefficients for trophic group abundances and moisture were generall y positive. Temperature was negatively correlated with the three funct ional groups in the L horizon only. Bacterial and hyphal feeding nemat odes showed a significant decrease with time in the L layer, reflectin g diminishing substrate quality (and food availability) during decompo sition. A significant annual periodicity could be demonstrated for bac terial feeders in L litterbags and plant feeding nematodes in the H ma terial.