Effects of 137Cs and 90Sr on structure and functional aspects of the microflora in agricultural used soils

At long sight 137Cs and 90Sr are the main radionuclides responsible for the contamination of agricultural soils due to core melts in nuclear power plants such as Chernobyl or Fukushima. Once deposited on the soil surface, the two radionuclides remain in the upper soil layer for several decades. In the upper soil layer the highest microbial activity can be found, due to high organic matter contents, warm temperatures and gas exchange with the atmosphere. Hence, in contaminated soils microorganisms in upper soil layers (e. g. the plow layer on agricultural fields) are exceedingly exposed to radioactivity. However, no data are available how radioactive contaminations with 137Cs or 90Sr in a realistic order of magnitude affect the microbial community and its functions in soils. This dissertation discusses the effects of radioactive contaminations on the microbial community structure and some of its functions in soils. Therefore, typical agricultural soils, an Orthic Luvisol from field site Merzenhausen and a Gleyic Cambisol from field site Kaldenkirchen-Hülst were artificially contaminated with various concentrations of 137Cs and 90Sr and partly applied with radiolabeled substrates and incubated in soil microcosms under controlled laboratory conditions. The lower radionuclide concentrations corresponded to the contaminations in the Chernobyl exclusion zone, the higher concentrations were up to 50-fold that of the maximum occurring hotspots (137Cs) in this zone. In three experiments the effects of the ionizing radiation on the bacterial and the fungal community structure (16S and 18S rDNA DGGE), the degradation of 14C-labeled wheat straw or uniformly ring-labeled 2,4- dichlorophenoxyacetic acid, the development of the fungal biomass (ergosterol quantification) and the chemical composition of the soil organic matter (13C CP/MAS NMR) were investigated. In half of the microcosms the soils were autoclaved and reinoculated with native soil, with intention to enhance the microbial growth.