The influence of tree species on the biomass of denitrifying bacteria in gray forest soils

The biomass of two groups of microorganisms was studied in gray forest soils under six tree species (spruce, Scotch pine, Arolla pine, larch, birch, and aspen) and in the soil of a layland (a clearing in the forest) using kinetic methods. The biomass was the highest in the soil of the layland. The lowest (19.4 mu g C/g of soil) biomass of heterotrophic microorganisms was found in the soil under the birch trees, and the highest one (41.7 and 32.0 mu g C/g), under the pine and spruce ones. The biomass of denitrifying microorganisms was lower by thirty times than that of the heterotrophic ones. In the soils under the pine and spruce trees (8.4 and 9.2 mu g C/g, respectively), the biomass of the denitrifying microorganisms was the lowest; under the birch and larch trees, it was the highest (16.7 and 13.7 mu g C/g).