SOIL NEMATODE FAUNA OF A SUB-ARCTIC HEATH - POTENTIAL NEMATOCIDAL ACTION OF PLANT LEAF EXTRACTS

Dwarf shrub heaths are common vegetation types of the Arctic and Subar ctic. Some of the dominant plants in these communities release toxic s ubstances which can affect neighbouring plants. We investigated the ef fects of leaf extracts from two dwarf shrubs, Cassiope tetragona and E mpetrum hermaphroditum, and from mountain birch, Betula pubescens spp, tortuosa, on nematode community structure and reproduction in a pot a nd an agar culture experiment. In pots two graminoids, Carex bigelowii and Festuca vivipara, were grown in previously sterilized or non-ster ilized soil. Soil was collected from a subarctic heath, and plants fro m a fellfield site, near Abisko, northern Swedish Lapland. The natural ly occurring nematode community at the heath site is also described, A total of 34 nematode taxa were observed at the field site and 32 taxa in the pot experiment. Most species, especially frequent taxa, occurr ed in both soils. Potted soil was strongly dominated by bacterial feed ers and showed a shift towards a more colonizer controlled population. These changes were presumably due to the establishment of residual sp ecies after freezing and/or sterilization of the soil prior to incubat ion in the laboratory. Direct exposure of the nematode Aphelenchoides saprophilus to the leaf extracts in agar cultures resulted in a lower reproduction rate. Leaf extract treatment in potted soil altered nemat ode species composition and dominance structure, and generally reduced species number and maturity index. The diversity of genera was decrea sed by all extract treatments in pots with Carer, Nematode population density was not affected, except after application of Betula extracts, where significantly higher densities occurred. Nematode data were rel ated to respiration and active fungal biomass in the soil, indicating that rather than allelochemicals with nematicidal properties, carbohyd rates in the leaf extracts promoting a beneficial microflora may have affected the nematode community. (C) 1998 Elsevier Science B.V.