Microbial immobilization and recycling of 137Cs in the organic layers of forest ecosystems: relationship to environmental conditions, humification and invertebrate activity

The 137Cs content of the microbial biomass in the organic layers of 10 German forest sites was quantified with a modified fumigation/extraction method. A KCs factor was calculated for biomass 137Cs from the difference between unfumigated and fumigated samples by means of laboratory cultures. The size of the estimated KCs factors varied between 1.54 and 2.90 (mean, 2.17; S.D., 0.48). The microflora at the different forest sites contained between 1 and 56% of the total amount of 137Cs found in the organic layers (mean, 13%). Litterbag experiments showed that 137Cs was actively transported into the L layer by the microflora and that this effect was enhanced by the mesofauna. It is concluded that the immobilization and recycling of 137Cs by the microflora in the organic layer of forest soils is determined by three major factors: 137Cs availability, growth conditions of the microflora and biotic interactions.