Effects of sulphur dioxide pollution on forest soil microorganisms

Abstract

Investigations were conducted to compare the forest soil microflora of three "ecologically analagous" sites, 1, 2, and 3, situated 2.8, 6.0, and 9.6 km, respectively, downwind of a sour gas plant emitting SO2. Bacteria and fungal propagules were isolated by dilution plating, and relative tolerance to the dissociation products of SO2 was tested by plating onto media also amended with Na2SO3 or NaHSO3. There were significant reductions both in total numbers of bacteria and starch-utilizing bacteria from the organic soil (F/H horizon) of site 1. A greater proportion of the bacteria from site 1 were spore formers compared with sites 2 and 3. There was no significant difference between sites in the number of fungal propagules isolated from the organic soil, but a smaller proportion of fungi recovered from site 3 were tolerant to sulphite or bisulphite compared with sites 1 and 2. No differences between sites were detected in terms of bacterial tolerance to the dissociation products of SO2. There were no major differences in the numbers of microorganisms isolated from the mineral soil or in their tolerance to bisulphite or sulphite, although in September, fewer bacteria were isolated from site 1, and a greater proportion of these were spore formers.