Effects of dry-deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter I. Changes in communities of fungal saprotrophs

SUMMARY Comparisons of the saprotrophic fungi isolated from ash (Fraxinus excelsior L.), birch (Betula spp.), hazel (Corylus avellana L.), pedunculate oak (Quercus robur L.), sessile oak [Q. petraea (Mattuschka) Liebl.] and sycamore (Acer pseudoplatanus L.) leaf litters from three woodlands exposed to low, medium and high levels (c. 0 0-> 0 060 ,ul '1) of sulphur dioxide (SO2) showed that the composition of the fungal communities differed between sites. Fumigation of angiosperm tree leaf litters from the least and the most polluted site with environmentally-realistic concentrations (0 010-0 030 l l-1) of SO2 for 16-68 wk in an open-air field-fumigation experiment resulted in marked changes in the composition of the fungal communities in the leaf litters, comparable with differences found between the woodland sites. Cladosporium spp., Epicoccum nigrum Link, Fusarium spp. and Phoma exigua Desm. were less commonly isolated from leaf litters exposed to SO2, whereas Coniothyrium quercinum Sacc. var. glandicola Grove, Cylindrocarpon orthosporum (Sacc.) Wollenw. and Penicillium spp. were more frequently isolated from fumigated litters. However, few differences could be detected in the response to S02 of the mycofloras of leaf litters originating from different woodland sites. In general, S02 did not affect the total extent of fungal occupancy of the microsites in the litter, as fungal species which decreased in abundance on exposure to the gas appeared to be replaced in the litter by other species more tolerant to the gas. SO2 therefore appeared to be selectively toxic to saprotrophic fungi isolated from these litters.