THE EFFECT OF WILDFIRE ON THE OPPORTUNISTIC DECOMPOSER FUNGAL COMMUNITY OF A URUGUAYAN EUCALYPTUS SPP FOREST

Fungal communities from the A horizon of an Eucalyptus forest sandy so il, in Rocha, Uruguay, were analyzed. Two proximate sites, one affecte d by fire (site A) in January 1989 and the other undisturbed (site B), were selected. The composition and organization of both communities w as revealed th rough the analysis of 240 samples collected eight times over 12 months period (March, April, May, June, August, October, 1989 ; January and April 1990). From these samples, 125,862 isolates belong ing to 159 taxa were obtained. At both sites, the propagules of the op portunistic decomposer remained scarce throughout the year. and the nu mber of species per 100 isolates was very low. At site A, Gongronella butleri was the dominant species during the year, except in March, whe n Eupenicillium brefeldianum, Penicilium decumbens and Talaromyces fla vus codominated. At site B, Gongronella butleri, Penicillium fellutanu m and Penicillium donkii codominated or alternated their dominance. Th e index of Similarity between both sites was 44% which reflects that t he differences between microfungal populations of both soils represent ed more changes in species number of propagules than in species compos ition, except in the first sampling month. It seems, consequently, tha t the fire was not damaging enough to modify the composition of the fu ngal opportunistic decomposer community. However, the higher number of propagules at burned site A than at undisturbed site B suggests that, in the former site, some fungal populations were favored. This could be due to the rainfall during late March 1989 (at the start of the sam pling), which stimulated Eucalyptus regrowth and also Acacia and Eucal yptus seed germination, two to three months after the fire. Consequent ly, early new conditions not far from that of undisturbed site B were established and the resilience of fungal soil populations of site 4 se ems to be high due to early regrowth of the vegetation.