We studied the seasonal change in radiocesium (137Cs) and potassium (K) concentrations in current leaves and branches in Pinus densiflora (naturally regenerated saplings), Cryptomeria japonica (planted saplings) and Quercus serrata (planted and sprouted saplings) in Tamura, Fukushima, Japan. Current year shoots were collected from June 2016 to December 2017 at intervals of one to four months. For deciduous species of Q. serrata, we also collected dead leaves that still attached on branches in December. All collected shoots were divided into leaves and branches and the samples were grounded. The concentration of 137Cs was measured by a germanium semiconductor detector. K concentration was quantified by ICP-AES method. Regardless of tree species, there were seasonal changes in 137Cs concentration, and those concentrations were higher in young leaves and branches at May or June, while the concentrations decreased thereafter and the change was relatively small from August to winter. Decreasing of 137Cs concentration in dead leaves in Q. serrata also observed in several individuals in December. This reduction may indicate reabsorption of 137Cs in leaves before shedding. K concentration was also higher in the younger leaves compared with the mature leaves. A positive relation between 137Cs and K concentration in leaves was observed in P. densiflora, C. japonica, and sprouted Q. serrata. From these results, 137Cs was thought to be high at relatively younger organs with higher K concentration in those three species.

06 - Seasonal changes in radiocesium and potassium concentrations in current year shoots in three tree saplings in Fukushima, Japan