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Activity and biomass of soil microorganisms at different depths

Lavahun, M.F.E., Joergensen, R.G., Meyer, B.
Biology and fertility of soils 1996 v.23 no.1 pp. 38-42
soil microorganisms, biomass, soil organic matter, microbial activity, soil depth, arable soils, grassland soils, plant residues, degradation, mineralization, soil heterogeneity, Germany
We measured microbial biomass C and soil organic C in soils from one grassland and two arable sites at depths of between 0 and 90 cm. The microbial biomass C content decreased from a maximum of 1147 (0-10 cm layer) to 24 micrograms g-1 soil (70-90 cm layer) at the grassland site, from 178 (acidic site) and 264 micrograms g-1 soil (neutral site) at 10-20 cm to values of between 13 and 12 micrograms g-1 soil (70-90 cm layer) at the two arable sites. No significant depth gradient was observed within the plough layer (0-30 cm depth) for biomass C and soil organic C contents. In general, the microbial biomass C to soil organic C ratio decreased with depth from a maximum of between 1.4 and 2.6% to a minimum of between 0.5 and 0.7% at 70-90 cm in the three soils. Over a 24-week incubation period at 25 degrees C, we examined the survival of microbial biomass in our three soils at depths of between 0 and 90 cm without external substrate. At the end of the incubation experiment, the contents of microbial biomass C at 0-30 cm were significantly lower than the initial values. At depths of between 30 and 90 cm, the microbial biomass C content showed no significant decline in any of the four soils and remained constant up to the end of the experiment. On average, 5.8% of soil organic C was mineralized at 0-30 cm in the three soils and 4.8% at 30-90 cm. Generally, the metabolic quotient qCO2 values increased with depth and were especially large at 70-90 cm in depth.