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1 Polish Journal of Ecology

1 2001

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Drained fens : comparison of nitrogen mineralization rate and biotic structures in two periods of secondary succession

Kajak A., Pętal J.

Polish Journal of Ecology

2001

Vol. 49, nr 3

261-270

The grassland on drained fens, differentiated by water holding capacity and soilorigin, derived from sedge-moss (SMP), tall-sedge (TSP) and alder peat (AP) were compared in terms of soil properties, N mineralization rate and composition of dominant microbial and faunal communities. Comparison was done for two periods of secondary succession: 15 (earlier or first period) and 30 years after drainage (later or second period). In both compared period soil properties remained significantly different between study sites, however differences in respect to biota were lower in the later period. In all compared sites in the second period a decrease was noted in soil moisture, pH and total C and N contents accompanied by an increase in bulk density and cation-exchange capacity. The periodically over-dried AP grassland differed significantly from moist grasslands, located on segde originated soils. The rate of nitrogen mineralization was the highest in AP soil in both periods compared, but decomposition of new, dead plant material was retarded. Amount of N accumulated in plant detrius accounted for 30, 42 and 91% of live plant biomass in compared SMP, TSP and AP sites, respectively. The low efficiency of soil organisms in the decomposition of detritus in AP soil may be illustrated by relations between invertebrate biomass and the amount of accumulated detrius. Nitrogen in soil invertebrates contributed to 81% of total N in litter in both sedge originated grasslands and to 19% only, in alter grassland. The decrease in the number of microbivorous and plant parasitic nematodes, stimulating mineralization processes was noted in AP soil in the second period. The density of humus forming invertebrates (Enchytraeidae, Lumbricidae) was significantly lower there in both periods. The paper focusses on historical processes to explain the discrepancy between low abundance of humus forming invertebrates and high humus content in alter soil.