Simple laboratory methods have been developed for studying, under defined conditions, the colonization of cellulose substrata by soil micro-organisms. The substratum is placed on the surface of soil samples in Petri dishes and colonization followed by direct microscopic examination in situ and also by removing small pieces of colonized material for more critical study. Such factors as soil moisture, nutrient status and pH may be varied and their influence determined. In our studies the cellulose used was lens tissue and soil moisture was always maintained at ‘field capacity’. The factors varied were pH, nitrate and phosphate. The detailed effects of varying these factors depended on soil type but a striking feature was the small range of cellulolytic species found in any treatment. Generally, only one or two species were actively involved. The treatments all produced marked and consistent changes in the qualitative composition of the colonizing cellulolytic flora. These results emphasize the precise control of the environment in selecting individual members from a group of soil organisms all competent to degrade a particular substrate. They also have implications for the study of micro-environments in the soil. It is generally considered that the soil constitutes a mosaic of environments usually of too small a size for detailed analysis. By extension of the methods adopted here it appears that it would be possible to create on a sufficiently large scale a great many of the situations which occur naturally on only a micro-scale.
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