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Update:November 12, 2020

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Turnover of fine roots changes the distribution of radiocesium in soil decades later

Article title

Assessment of vertical radiocesium transfer in soil via roots

Author (affiliation)

Wataru Sakashita (a,b), Satoru Miura (a), Akio Akama (a), Shinta Ohashi (a,c), Shigeto Ikeda (a,b), Tomoyuki Saitoh (d), Masabumi Komatsu (a,e), Yoshiki Shinomiya (a,b), Shinji Kaneko (f)

(a) Center for Forest Restoration and Radioecology, FFPRI, Tsukuba, Ibaraki, Japan.

(b) Department of Forest Soils, FFPRI, Tsukuba, Ibaraki, Japan.

(c) Department of Wood Properties and Processing, FFPRI, Tsukuba, Ibaraki, Japan.

(d) Tohoku Research Center, FFPRI, Morioka, Iwate, Japan.

(e) Department of Mushroom Science and Forest Microbiology, FFPRI, Tsukuba, Ibaraki, Japan.

(f) Kansai Research Center, FFPRI, Kyoto, Japan.

Publication Journal

Journal of Environmental Radioactivity、Volume 222 106369、ELSEVIER、October 2020 DOI:10.1016/j.jenvrad.2020.106369( External link )

Content introduction

Understanding the changes that have occurred in the distribution of radiocesium in forest soils after the Fukushima Daiichi Nuclear Power Plant accident is essential for estimating the amount of radiocesium that is absorbed by trees from the soil and for restarting the forestry industry in contaminated areas. The radiocesium that derived from the nuclear accident has been fixed by clay minerals, and it is thought that most of that is currently remaining in the surface mineral soil layer. However, radiocesium from global fallout (produced more than a half century ago) has penetrated deeply into forest soils, and there are many things about the long-term process of the downward movement of radiocesium that are still unknown. Resolving these issues is important for predicting the movement of radiocesium in forest soils.

This study focused on the role of “fine roots” that provide nutrients (such as potassium) to the soil through the turnover processes (root production, mortality and decomposition). The authors studied the radiocesium inventory (Bq/m2) in both fine roots and soil matrices at various study sites dominated by various plant species (cedar, cypress, etc.). As a result, they found that the ratio of radiocesium inventories of fine roots to the soil matrices was about 1% in 0-10cm soil layers, while it was about 2% in soil layers deeper than 10cm. This result suggests that when there is a continuous turnover process (production, mortality and decomposition) of fine roots over a period of decades, there is a gradual decrease in the differences in radiocesium inventory between surface mineral soil and soil that is deeper than 10cm. Thus, the vertical distribution of radiocesium in forest soils may change over a time scale of decades. This research should help to improve the accuracy of predicting the long-term movement of radiocesium in forest soils.


Figure:Schematic diagrams
Figure:Schematic diagrams of the long-term downward movement of radiocesium in forest soils via fine roots.

a) Most of the radiocesium is stored in the surface mineral soil, but b) the radiocesium activity concentration in fine roots (growing sections) is high, and c) the subsequent fine root mortality and decomposition d) may transfer radiocesium to deeper parts of the forest soil.