NUMBERS AND VIABILITY OF VESICULAR-ARBUSCULAR FUNGAL PROPAGULES IN FIELD SOIL SAMPLES AFTER WILDFIRE

At two N.W. Spanish sites affected by forest fires during the summer of 1988, burnt plots and neighbouring control plots were sampled every 4 months during the following year to study (a) the effect of burning on the vesicular-arbuscular (VA) fungal propagules present in the soil, and (b) the colonization of the post-fire vegetation by VA fungi. The burnt plots had lower viable propagule densities than the control plots, as measured by the most probable number method and by spore counts, and VA colonization of the post-fire herbaceous vegetation (grasses) was less intense on burnt plots than on control plots. Spores of Acaulospora laevis (the species that dominated before burning) had lower germination rates when collected from the burnt plots than from the unburnt plots, and 1 yr after burning A. scrobiculata was the dominant species on burnt plots at the site with the steeper slope.