Particle size fractionation
Springer Online Journal Archives 1860-2000
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Abstract Low atmospheric H2 concentrations (0.55 ppmv) are oxidized in soils by a high-affinity activity with typical characteristics of an abiontic soil enzyme. This activity was measured in a meadow cambisol and a forest cambisol. In both soils, the maximum activity was reached at a soil moisture of about 20% water-holding capacity, and was localized in the top Ah horizon. The soils were fractionated by dry sieving and wet filtration into nine different particle-size fractions, ranging from 3 to 2000 μm in size. H2 oxidation was measured by three different assays and was compared to the ATP content and microscopic counts of bacteria in the same fractions. In the meadow soil, the specific activities of H2 oxidation increased with the particle size (maximum at 200–500 μm), whereas ATP and bacterial counts showed no trend. In the forest soil, the specific activities of H2 oxidation increased with the particle size up to 50–100 μm, and then decreased again. ATP and bacterial counts, however, showed the opposite trend, i.e., decreased with an increasing particle size. Thus the H2-oxidizing activity was not correlated with characteristic microbial biomass parameters. Although significant percentage (29–64%) of randomly isolated heterotrophic bacteria was able to oxidize H2, this activity was too small to account for the H2 oxidation in the soil. In both soils, most of the activity present was found in particles of 100–500 μm in size. The recovery shifted to smaller size fractions when larger soil aggregates were broken up by wet instead of dry sieving. Attempts to extract the H2-oxidizing activity from the soil particles were unsuccessful.
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