Post-drainage secondary succession of soil nematodes on fen peat meadows in Biebrza Wetlands, Poland

After the drainage of fens and their permanent use as meadows, peat-forming process is being replaced by moorshing (mucking) process (mineralization and humification of peat), and then by turf-forming process. Secondary succession of soil nematodes was examined by using the chronosequence of meadow sites (period I: 1978-1983) and also by analysing the same sites 15-17 years later (period II: 1994-1997). The analysis was focused on the taxa (genera) of nematodes and on 19 to 29 parameters describing the community as total density, density of trophic groups, diversity indices and maturity indices. The pattern of successional changes was obtained for periods from 2 to 117 years after drainage. Natural not-drained fens were used for comparison. Soil structure and soil processes occuring over the time considered can be characterized as follows: soil moisture (by weight) 80-52% total soil porosity 90-77%, bulk density 0.16-0.44 (to 0.92) g cm^-3, total C content in soil 47-7% total N content in soil 4.4-0.5%, ranges in the sequence from Mt I (poorly moorshified soils) to Mt III (strongly moorshified soils). In natural fens, soil moisture was 80%, soil porosity 90%, bulk density 0.15-0.35 g cm^-3, and peat-forming processes (Pt) were continued. As compared with natural fens, drainage and management of fens was associated with increasing density of total nematodes and their components such as bacterivores, fungivores, facultative plant feeders, obligate plant feeders, omnivores, and predators. In drained fens the density of nematodes declined with succession with the exception of omnivores. The increase in the density of omnivores was positively correlated with the number of years after drainage (r=0.48, P<0.01). The indices of taxa diversity and maturity indices were postively correlated with years after drainage (P<0.001-0.05). In natural fens, ranges of density of all trophic groups were lower, and maturity indices higher than in drained peat meadows. The The mechanisms driving the first stage of succession in nematode communities (until about 30 years after the drainage of fens) seem to be tolerance to the droughts and to the excess of nitrogen what was accompanied with higher density of herbivores (mainly Paratylenchus). In later stages, interspecific competition is likely to play a more important role. Also a statistically significant relation was found of some taxa and parameters to peat type.