A through year behavior of 137Cs in a Japanese flowering cherry tree in relation to that of potassium.

To understand the transfer of radiocesium (137Cs) in inside of deciduous trees, changes in 137Cs activity concentrations, primarily derived from the Fukushima accident in March 2011, were observed in the upper parts of a Japanese flowering cherry tree (Prunus x yedoensis cv. Somei-Yoshino) between 2015 and 2018. The sampling of the foliar parts occurred over the entire leaf life span from winter bud to litterfall and those of the branches were distinguished based on emergence years (2017, 2016, 2015, 2014-2011, and 2010/before). First, every tissue demonstrated a clear seasonal variation in 137Cs activity concentration. Second, a synchrony of seasonal variations in 137Cs activity concentration with those in the biological analogue of K concentration was observed in foliar parts during their growth season, but not in branches nor during the other seasons. With respect to the timing of changes in each tissue with tree phenology, it is possible that K and 137Cs alternate between leaves and branches via the same translocation mechanisms. The resorption efficiencies (i.e., 1 - [the concentrations in the last litterfall]/[the maximum concentrations in green leaves]) of K and 137Cs were 76% and 46% in average, respectively. In addition, both leaf buds and branches played an important role as reservoirs during dormancy. The buds storage ratio before and after bud burst (i.e., [the inventories in buds at the end of defoliation]/[those before and after bud burst]) for K were 0.57 and 0.10 in median, respectively, and those for and 137Cs were 1.14 and 0.14 in median, respectively. Consequently, the transfer of 137Cs in inside of trees was still visible seven years after deposition, even though the annual reduction in 137Cs activity concentration was apparent in each tissue.