Microfungal Populations in Surface Soils of Manipulated Prairie Stands

Comparisons of populations of soil microfungi from surface soils of bare, mulched, harvested, and recently burned prairie stands, with those from a dry—mesic control stand (1 year post—burn), revealed some remarkable distribution patterns for various fungal isolates. With the exception of the harvested and the control stands, little similarity could be found among any of the populations. Furthermore, the overall species composition of the populations showed little resemblence to populations isolated from within the dry—mesic segment of the prairie continuum in southern Wisconsin. Numbers of fungi and bacteria also exhibited a great deal of variation depending on the stand treatment. The most significant variations in microbial density included reductions in the numbers of fungi in the bare stand and major increases in fungal densities in the recently fired stand. Bacterial counts were higher in the mulched and the burned stands, but significantly lower in the bare stand, and greatly reduced in the moss—covered harvested stand. Manipulation of the dry—mesic prairie stands so altered the microbial balance that the resulting populations differed more than those reported earlier for the entire prairie continuum. Certain physiochemical properties of the microenvironment are important in the selection of prevalent fungi isolated from these stands. Evidence shows that a post—fire f ungal bloom occurs following grassland fires. Coniochaeta discospora and C. tetraspora, two pyrenomycetes, accounted for 60% of all isolates recovered from the burned stand. Both of these fungi produce ascospores whose dormancy is not readily broken.