Dynamics and stratification of functional groups of nematodes in the organic layer of a Scots pine forest in relation to temperature and moisture

Abstract

Nematode trophic groups were studied in litterbags in a Pinus silvestris forest using sampling periods of 8 weeks during 2.5 years. Temperature, moisture relationships and annual periodicity of nematodes were analyzed in the litter (L), fragmentation (F) and humus (H) horizons. Litterbags containing L, F and H material were placed in stacks and buried in the organic layer. Undisturbed core samples were used to compare the nematode abundance under normal field conditions with that in the litterbags. Time dependence of population growth and colonization was also studied in separate litterbags that were replaced every 8 weeks. During the first 4 to 6 months of the experiment, nematodes in the litterbag stacks grew rapidly to circa 5×10⁶m^–2. After that period, abundance gradually decreased to about 2.5×10⁶m^–2. These abundances were similar to those found in undisturbed cores. Nematode abundance during the first year was most pronounced in the top (L) litterbags; subsequently densities were more or less the same in the three organic horizons, reflecting the gradual change of L to F material. On average, during 2.5 years, bacterial feeding nematodes were the dominant 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 significantly between layers. In the first 2 to 4 months, hyphal feeding nematodes equalled the bacterial feeders in the L layer. Later bacterial feeders became dominant. The highest number of plant feeding nematodes was found in the F litterbags. Significant effects of temperature and moisture were mainly found on bacterial feeding nematodes. Regression coefficients for trophic group abundances and moisture were generally positive. Temperature was negatively correlated with the three functional groups in the L horizon only. Bacterial and hyphal feeding nematodes showed a significant decrease with time in the L layer, reflecting diminishing substrate quality (and food availability) during decomposition. A significant annual periodicity could be demonstrated for bacterial feeders in L litterbags and plant feeding nematodes in the H material.