Cesium, rubidium and potassium content in the needles and wood of Japanese cedar trees harvested from the sites of different radiocesium deposition levels

Abstract

To elucidate uptake via the roots and the dynamics of cesium (Cs) in Japanese cedar (Cryptomeria japonica D. Don), we measured the stable cesium (¹³³Cs), rubidium (Rb), and potassium (K) content in the needles and wood of Japanese cedar harvested from four sites: 1) Kawauchi; 2) Kamikawauchi; 3) Otama; and 4) Tadami in Fukushima Prefecture, Japan. The levels of deposition of radiocesium were different among sites. The contents of ¹³³Cs, Rb, and K were higher in current needles and heartwood than in old needles and sapwood, respectively. In addition, ¹³³Cs, Rb, and K content tended to be lower in the small than in the large trees. This result suggests that Cs would be accumulated in heartwood, particularly in mature trees. Proportional relationships were observed between ¹³³Cs in old needles and heartwoods as well as sapwoods. Therefore, ¹³³Cs in wood may be estimated from ¹³³Cs in needles. ¹³³Cs in needles and wood varied among sites, with higher levels observed in Tadami and Kamikawauchi. Exchangeable K in surface soil was slightly lower in Tadami and Kamikawauchi than in Kawauchi and Otama. Soil exchangeable ¹³³Cs was the highest in Tadami. The ¹³³Cs uptake via roots and the dynamics of ¹³³Cs in Japanese cedar may be affected by soil exchangeable K and ¹³³Cs.