Fumigation-extraction method to estimate microbial biomass in heated soils
Diaz-Ravina, M. | Prieto, A. | Acea, M.J. | Carballas, T.
A fumigation-extraction method that measures the fraction of the biomass rendered extractable to K2SO4 after microbial cells lysis chloroform was used to estimate microbial biomass C and N in forest soil samples unheated or heated at 160, 350 or 600 degrees C for 30 min, 2 or 4 h. The biomass C and N of the unheated samples were 1011 microgram C g-1 and 124 microgram N g-1 dry soil. Chloroform fumigation the heated samples did not solubilize non-microbial soil organic matter. The microbial C and N in the heated samples were reduced to undetectable amounts regardless of the temperature and duration of heating. After restoring the microbial population in the heated soils by inoculation with fresh unheated soil and incubation, microbial biomass C and N were detected in the samples heated at 160 degrees C (441 microgram C g-1 and 42 microgram N g-1 dry soil) and 350 degrees C (63 microgram C g-1 and 11 microgram N g-1 dry soil) whereas the values in samples heated at 600 degrees C were below the limits of detection. The decrease in biomass values were in accordance with a decrease in the number of microorganisms and hyphal length the recovery of which was inversely related to the temperature of heating. The results suggest that the fumigation-extraction technique can be used to estimate microbial biomass C and N in heated soils.
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