Population Dynamics of Soil and Vegetation Protozoa

Abstract

synopsis. Many fresh-water protozoa can be found in litters and soils, but the ubiquitous species are those which are able to oope with fluctuating moisture conditions. Terrestirial protozoa are more characteristic of bryophyte-soil habitats than aquatic ecosystems. Nutritionally, two groups have evolved in response to the plant commu? nity: naked, predominantly bacterial feeders, whose abundance is determined by the decomposability of the litter in which they live; and the slow growing, humusassociated testacea, which are more abundant in the litters of slow decomposability. Ubiquitous species comprise about 90% of the protozoa in soils. More continuous moisture conditions enhance the appearance of additional species. Hence species di? versity indicates higher moisture content of a soil. Protozoa may contribute to the functioning of the soil ecosystem by inducing flocculation of bacterial populations and recycling of minerals through ingestion of bacteria and excretion of soluble products. The surface of vegetation appears to represent the most terrestrial habitat a protozoan can exploit, because in contrast to the litter-soil ecosystem, only one species, Colpoda cucullus, dominates the population. Protozoa are the third most abundant, but the least understood, group of orga? nisms in the soil. This paper seeks to elucidate their possible role in soils by tracing their population dynamics, and is based largely on personal studies of several terrestrial biomes. Previously published work from this laboratory and the contributions and ideas of other authors are cited.