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To Develop Technique for Reducing Radiocesium Contamination of Trees: Potassium Fertilization Inhibited Cesium Uptake via Tree Roots


Article title

Potassium fertilisation reduces radiocesium uptake by Japanese cypress seedlings grown in a stand contaminated by the Fukushima Daiichi nuclear accident

Author (affiliation)

Masabumi Komatsu (a), Keizo Hirai (b), Junko Nagakura (b), Kyotaro Noguchi (b, c)

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

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

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

Publication Journal

Scientific Reports, 7:15612, November 2017, DOI: 10.1038/s41598-017-15401-w( External link )

Content introduction

To reduce radiocesium levels of trees contaminated by the Fukushima Daiichi Nuclear Power Plant accident, we conducted potassium fertilization to Japanese cypress (Chamaecyparis obtusa) seedlings in the eastern region of Fukushima (Figure 1, 2). Our results demonstrated that potassium fertilization inhibits absorption of radiocesium from soil by trees (Figure 3, 4).

Potassium fertilization has been effective in inhibiting the absorption of radiocesium from soil in agricultural crops. However, it is not completely known in case of trees. Additionally, for accurately evaluating the amount of radiocesium absorption from soil, it is necessary to use trees without direct contamination by the accident. Accordingly, in June 2014, we planted Japanese cypress seedlings and fertilized them with potassium chloride (100 kg ha−1 as K2O) two times (August 2014 and April 2015). In October 2015, the 137Cs concentration in needles, stems, and roots of fertilized seedlings remained at 12%, 20%, and 23% of the unfertilized ones, respectively. These results suggested that potassium fertilization had an inhibitory effect on the absorption of radiocesium into trees.



Figure 1. (a) The study site is located in the south part

Figure 1.
 (a) The study site is located in the south part of Kawauchi village, Fukushima. The site is marked by red circle and deposition levels of radiocesium obtained by aircrafts monitoring are plotted on the map.

 (b) The study site in April 2015. Three-year-old Japanese cypress trees were planted.


Figure 2. (a) Japanese cypress seedlings used in the study

Figure 2.
 (a) Japanese cypress seedlings used in the study.

 (b) Fertilization operation.

 (c) Potassium chloride fertilizer used in the operation.
 (d) Potassium fertilizer distributed across forest land (red grains).


Figure 3. 137Cs concentration in each part of Japanese cypress

Figure 3.

 137Cs concentration in each part of Japanese cypress seedlings (fertilized section: orange and unfertilized section: white).

 * indicates a statistically significant difference (nested-ANOVA, p < 0.05).


Figure 4. Relationship between exchangeable potassium

Figure 4. Relationship between exchangeable potassium concentration in 0–5 cm surface soil and aggregated transfer factor (Tag) in the needles sampled in the 2nd year (fertilized section: orange and unfertilized section: white). Tag indicates how easily radiocesium is absorbed from soil into trees. Soil exchangeable potassium refers to soil potassium that has the property of being absorbed into living organisms such as plants. Data on seedlings in the unfertilized section (white circles) show that trees absorb more radiocesium when there is little exchangeable potassium in the soil, confirming the effectiveness of potassium fertilization in inhibiting radiocesium absorption.