PROPERTIES AND COMPOSITION OF THE BACTERIAL FLORA OF A PINE FOREST SOIL

A study was made of the qualitative and quantitative distribution of aerobic heterotrophic bacteria in the two mineral horizons of a developing podsol soil under Pinus. There was no significant difference in the total numbers or in the kinds of bacteria between the two horizons. In the acidic A₁ horizon (pH, 3.6) Bacillus spp. comprised 58 per cent of the population, the remainder being composed of Gram-negative rods (15 per cent), pleomorphic rods (14 per cent), Gram-positive cocci (10 per cent) and streptomycetes (3 per cent). The corresponding figures for the C horizon (pH, 8.6) were Bacillus (23 per cent), Gram-negative rods (37 per cent), pleomorphic rods (10 per cent), Gram-positive cocci (17 per cent) and streptomycetes (13 per cent). These differences in distribution could not be related to any one environmental factor. The data from this investigation lend support to the view that different soil types can be distinguished by their bacterial floras. Bacillus subtilis, B. cereus and the Gram-positive cocci were biochemically and fermentatively active and many of the streptomycetes were able to degrade complex organic molecules. The Gram-negative and pleomorphic forms were apparently metabolically inactive.