Folia Microbiol.35, 561-569 (1990) Effect of Plant Waste on the Biomass and Abundance of Micromycetes in Alpine Soils A. ~IMONOVICOVA Institute of Experimental Biology and Ecology, Center of Biological-Ecological Sciences Slovak Academy of Sciences, 814 34 Bratislava, Czechoslovakia Received August 17, 1989 ABSTRACT. Examination of the total biomass of soil micromycetes and their abundance in four soil types in the Furkota Valley (High Tatra Mountains) modified by adding plant waste at 1 and 5 % revealed the following. The effect of the addition of organic matter was manifested by increased values of both the total biomass of soil micromycetes and their abundance. The highest values were always detected in soils to which the waste was added at 5 %. The effect of organic matter was most pronounced during the first phase of the experiment (from the beginning of the experiment up to 2-3 months). A gradual exhaustion of nutrients and energy resulted in decreased values. Natural forest and meadow ecosystems are permanently enriched by organic material, i.e. dead-plant matter and freshly shed conifer needles, leaves, cones etc., the so-called fall. A significant part of this organic matter is represented by cellulose, hemicelluloses and lignin, whereas proteins, lipids and other compounds are less frequent. Alpine soils, mostly with an acid reaction of the environment, have a high layer of plant waste which cannot be converted to humus by the soil microflora and zoo-edaphon during the vegetation period and the so-called crude humus is thus produced. The soil microbial biomass as a part of soil organic matter is highly sensitive to environmental changes (Sparling and Williams 1986). It was the aim of the present work to determine the biomass of soil micromycetes and investigate its changes in soil with added plant waste at 1 and 5 % under laboratory conditions.