Stem diameter dependence of cesium concentration ratio between stem and current-year branches in Quercus serrata

Le résumé fourni par la source

To systematically produce shiitake mushroom logs with radioactive cesium (137Cs) concentrations below the guideline level in areas affected by the Fukushima nuclear accident, accurate and efficient methods for predicting the 137Cs concentration in konara oak (Quercus serrata) stems at the harvest stage are essential. As part of developing a method to predict the future 137Cs concentration in stems coppiced after the accident based on the concentration in current-year branches at the juvenile stage, we investigated whether the 137Cs concentration ratio between the stem and current-year branches (CRstem/cy-branch) depends on stem diameter. Because stems at the harvest stage retained surface contamination of 137Cs from fallout, the naturally occurring stable isotope 133Cs was used as a substitute for 137Cs after confirming its validity. CRstem/cy-branch was calculated based on concentrations during the dormant season (November – April). The analysis revealed a stem diameter dependence of 133Cs CRstem/cy-branch, with larger stems exhibiting lower CRstem/cy-branch values, attributed to an increased biomass proportion of heartwood, which has a relatively low 133Cs concentration. However, no clear relationship was observed at sites with a narrow diameter range. Nevertheless, for trees with stem diameters of 10–20 cm, CRstem/cy-branch values were consistent across sites. Thus, a geometric mean CRstem/cy-branch value of approximately 0.32 is considered an appropriate estimate for stems with diameters of 10–20 cm and can also be used as a conservative estimate for stems over 20 cm. For future predictions, further investigation is needed to determine whether the 137Cs concentration in current-year branches changes between the juvenile and harvest stages.

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