Several years after the Fukushima Daiichi Nuclear Power Plant accident, the surface mineral soil layer is believed to be the main reservoir of radiocesium (¹³⁷Cs) in forest ecosystems in Japan. Dissolved ¹³⁷Cs combines with clay minerals in the soil, and hence, it is not expected to easily infiltrate over time. However, previous studies have indicated that ¹³⁷Cs derived from the older global fallout migrated deeper than that of the Chernobyl accident, and this cannot be explained by only the dissolved ¹³⁷Cs vertical migration in the soil. Considering the carbon and nutrient dynamics in the forest floor, the ¹³⁷Cs transfer process in soil via roots may alter its vertical distribution on a decadal scale. Therefore, in this study, we investigated the ¹³⁷Cs activity concentrations in both roots and soil matrix, by considering four (0–20 cm) or six (0–30 cm) mineral soil layers taken at every 5 cm at seven study sites dominated by one of the six plant species (three coniferous forests, one deciduous forest, two deciduous forests covered by Sasa, and one bamboo forest) in eastern Japan in 2013. Comparing the results of ¹³⁷Cs activity concentrations between roots and soil matrix taken at the same soil layer, roots at the surface (0–5 cm) layer often showed lower values than the soil matrix. However, roots deeper than 5 cm had higher activity concentrations than the soil matrix, conversely. The ¹³⁷Cs inventories ratio of roots to soil matrix are about 1% at the 0–5 and 5–10 cm soil layer, and about 2% at the soil layers deeper than 10 cm. These results suggest that decomposition of root litter little affect the short-term vertical migration of ¹³⁷Cs in the forest soil. However, it indicates that continuous production and mortality of roots with relatively high ¹³⁷Cs activity concentrations have an important role for changing the vertical distribution of ¹³⁷Cs on time scale of decades, particularly at deeper soil layers.

福岛第一核电站事故发生数年后，据信表层矿物土壤层是日本森林生态系统中放射性铯（¹³⁷ Cs）的主要储层。溶解的¹³⁷ Cs与土壤中的粘土矿物结合，因此，预计它不会随时间轻易渗透。但是，先前的研究表明，较早的全球辐射产生的¹³⁷ Cs的迁移比切尔诺贝利事故的迁移更深，这不能仅通过土壤中溶解的¹³⁷ Cs垂直迁移来解释。考虑到森林地面的碳和养分动态，¹³⁷Cs通过根在土壤中的转移过程可能会改变其垂直分布，年代际尺度。因此，在这项研究中，我们考虑了在七个主要研究地点每5 cm采集的四个（0–20 cm）或六个（0–30 cm）矿质土壤层，研究了根和土壤基质中¹³⁷ Cs的活性浓度在东日本在2013年的结果进行比较的6个植物物种之一（三级针叶林，一个落叶林，通过洒洒涉及两个落叶林，和一个竹林）^137个铯活度浓度根系和土壤基质之间的拍摄在相同的土壤层中，表层（0-5厘米）的根通常显示出比土壤基质低的值。但是，相反，深于5厘米的根比土壤基质具有更高的活性浓度。的在0-5和5-10 cm土层中，根与土壤基质的¹³⁷ Cs存量比约为1％，而在10 cm以上的土层中约为2％。这些结果表明，根凋落物的分解对森林土壤中¹³⁷ Cs的短期垂直迁移几乎没有影响。然而，这表明具有较高¹³⁷ Cs活性浓度的根的连续生产和死亡对于改变几十年来时间尺度上¹³⁷ Cs的垂直分布具有重要作用，尤其是在较深的土壤层。