Influence of A₀-Layer Removal on Radiocesium Concentration and the Amount in Lentinula edodes Fruiting Body, Bed-log, and Soil in Forest

Abstract

This study aimed to alleviate radiocesium pollution in Lentinula edodes (shiitake mushrooms) by using the bed-log cultivation method. In 2013, we set bed logs on the surface of A-horizon soil where A₀ layer was removed in 2012 in a forest located in Iwate Prefecture, Japan. Radiocesium concentrations or amounts of the treated plots were compared with those of non-treated plots for 5 years. In 2017, mean radiocesium concentration in bed logs collected from treated plots was 68％ of that in bed logs collected from non-treated plots. Radiocesium concentration was also reduced in fruiting bodies from treated plots. Radiocesium amount in A₀ layer decreased after the removal of A₀ layer, and this trend continued for at least 5 years, despite the supply of radiocesium from the canopy layer as litter. Radiocesium concentration in A₀ layer of treated plots was 46％ of that in non-treated plots in 2017. These results indicated the successful alleviation of radiocesium pollution in bed-log-cultivated L. edodes. However, 4 years after treatment, radiocesium amount in A-horizon soil (0-5 cm in depth) exceeded that of A₀ layer. Additionally, direct accumulation of radiocesium in A-horizon soil via L. edodes hyphae or adhesion onto bed logs due to rain splash is a matter of concern. Thus, currently, there is a risk of increased radiocesium pollution when the bed log is set directly on A-horizon soil.