RESUMO
The activity concentrations of radiocesium (137Cs) in wild mushrooms are reported to vary according to species, genus or ecological types. In addition, the concentration fluctuates among the same species collected within the same area. Therefore, we investigated whether the 137Cs concentration of wild mushrooms would be (1) spatially biased, or (2) influenced by the 137Cs or exchangeable potassium concentrations in the soils below. We set two survey plots 300 m apart in a Himalayan cedar forest in Tsukuba, Japan, where ca. 30 kBq/m2 of 137Cs was deposited after the Fukushima Nuclear Power Plant accident. From these plots, we collected fruit-bodies (fungal structures for spore production) of co-occurring Boletus hiratsukae, a mycorrhizal species, as well as from the soil below. The mean 137Cs concentrations in the fruit-bodies were significantly different between the two plots, but no difference was observed in the soil 137Cs concentration between the plots. Significant spatial autocorrelation was observed in the 137Cs concentration in the organic layer for both sites, but no significant spatial autocorrelation was observed in the 137Cs of fruit-bodies. Therefore, the variation in the 137Cs concentrations of co-occurred B. hiratsukae was not explained by spatial bias or radioactivity in the below soil. In contrast, the exchangeable potassium concentration in the soil was negatively correlated with the 137Cs in the fruit-bodies. Our results suggest that the 137Cs absorption of wild mushrooms would be suppressed by the competitive effect of exchangeable potassium in the surrounding soils.