Microbial biomass measurements in forest soils: The use of the chloroform fumigation-incubation method in strongly acid soils

doi:10.1016/0038-0717(87)90051-4

Soil Biology and Biochemistry

Volume 19, Issue 6, 1987, Pages 697-702

https://doi.org/10.1016/0038-0717(87)90051-4 Get rights and content

Abstract

Microbial biomass C and ATP were measured in 10 forest soils that ranged in pH from 3.2 to 7.2. A close relationship (r = 0.85) between biomass C (measured by the fumigation-incubation method, using the CO₂-C evolved from the non-fumigated soil in 10 days as the control) and ATP was obtained in soils with pH ⩾ 4.2. The average biomass ATP concentration was 9.1 βmol ATP g⁻¹ biomass C, similar to that found in earlier studies for soils above pH 4.2. There was also good agreement (r = 0.87) between biomass C as measured by fumigation-incubation and as measured by direct microscopy in soils of pH ⩾ 4.2, with an average ratio of one between the two measurements. However, in soils below pH 4.2, biomass C measured by the conventional fumigation-incubation method was very low compared to that estimated from soil ATP concentration or by direct microscopy.

Results with large inocula were inconclusive but it may be possible to measure microbial biomass in strongly acid soils by adding a large inoculum to the fumigated soil and using the appropriate value of k_C for that soil.

If biomass C in the strongly acid soils (pH < 4.2) is calculated from the CO₂-C evolved by the fumigated soil alone, without subtracting the control, a mean biomass ATP concentration of 9.2 μmol ATP g⁻¹ biomass C is obtained, a value virtually identical to that measured in the 6 soils of pH ⩾ 4.2 by the conventional method using a control. Biomasses calculated by this modified method in the strongly acid soils were also broadly comparable with those measured by direct microscopy. Soils at or below pH 4.2 contained very high concentrations of KCl-extractable aluminium. It is possible that this is linked to the reduced activity of microbial recolonizers in acid fumigated soils.

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