Do Chernobyl-like contaminations with 137Cs and 90Sr affect the microbial community, the fungal biomass and the composition of soil organic matter in soil?

137Cs and 90Sr are the main radionuclides responsible for contamination of agricultural soils due to core melts in nuclear power plants such as Chernobyl or Fukushima. The present study focused on effects of Chernobyl-like contaminations on the bacterial and fungal community structure, the fungal biomass and the formation of soil organic matter in native and in sterilized and reinoculated soils. 2% wheat straw [m/m] was applied to a typical agricultural soil, artificially contaminated with 137Cs and 90Sr, and it was then incubated in microcosms for three months at 20 °C and 50% of the water-holding capacity. The development of the microbial communities was monitored with 16S and 18S rDNA denaturing gradient gel electrophoresis (DGGE). The quantification of the ergosterol content was used as a proxy for changes in the fungal biomass. Changes in the soil organic matter were determined using the 13C cross polarization/magic angle spinning nuclear magnet resonance technique (13C-CP/MAS NMR). Slight but significant population shifts in the DGGE gel patterns could be related to the applied radionuclides. However, radiation-induced impacts could not be seen in either the chemical composition of the soil organic matter or in the development of the fungal biomass. Impacts caused by sterilization and reinoculation prevailed in the microcosms of the present study. Contaminations with 137Cs or 90Sr up to 50-fold that of the hotspots occurring in Chernobyl led to minor changes in soil microbial functions suggesting a strong resilience of natural soils with respect to radioactive contamination. -- Highlights: ► We observed the effects of Cs-137 and Sr-90 on microbial soil functions. ► The microbial community shifted slightly. ► The ergosterol content was not affected. ► The chemical composition of soil organic matter was also not affected. ► Effects caused by sterilization prevailed