Soil aggregates as microcosms of bacteria—protozoa biota

Abstract

Forty-eight air-dried soil aggregates were separately incubated under alternately submerged and dry conditions at 20°C without adding exogenous nutrients. In the course of submersions, the population dynamics of bacteria and protozoa were followed in each aggregate. It was shown that every aggregate accommodated at least three major groups of bacteria as categorized on the basis of colony forming curve (CFC) analysis. The growth of these bacterial groups occurred in sequence during submersion. Three to fourteen protozoan groups from each aggregate were detected as active forms. Distribution patterns of these groups among the 48 aggregates differed. The number of groups which were active simultaneously in each aggregate were small and the composition of groups changed gradually in the course of submersion. Frequency of appearance of each group during submersion was different and most groups appeared sporadically. These observations suggest that, in spite of the microbial diversity among aggregates, only a few groups are active concurrently.