Response of soil nematodes, rotifers and tardigrades to three levels of season-long sulfur dioxide exposures

Abstract

Soil nematode, rotifer, and tardigrade populations were sampled in field plots of native northern mixed prairie in southeastern Montana from 1977 to 1979. The field plots were exposed to season-long fumigation with controlled low-levels of SO2 throughout the growing seasons (April–October). Two field sites were used, one fumigated for five seasons (1975–1979) and the other for four (1976–1979). Seasonal average SO2 concentrations ranged from control (< 1 pphm) to approximately 7 pphm. Soil fauna were sampled by taking soil cores and extracting them by the Baermann wet funnel technique. Total counts were made for tardigrades and rotifers while nematodes were divided into three groups-stylet bearers (Tylenchida-Dorylimida), non-stylet bearers, and the predatory Mononchida. Consistent trends of substantial reductions in tardigrade populations occurred in all treated plots in all years; however, statistical significance was achieved only in 1979 when sample size and individual core size were substantially increased. Tardigrades were found to be restricted almost completely to the surface two centimeters of the soil profile. Significant population reductions in the treated plots of both sites were found for non-stylet bearing nematodes in 1977 only. Stylet bearing types and predaceus Mononchida appeared unaffected by the SO2 as were the soil rotifers, although slight but consistent trends of reduction in rotifers occurred in the highest treatments in 1977 and 1978. Both nematodes and rotifers were distributed primarily in the 0 to 10 cm layer of the soil profile but not restricted to the soil surface as much as the tardigrades. Implications of the responses to SO2 and vertical distributions of the three groups are discussed.