We studied seasonal changes in radiocesium (¹³⁷Cs) activity and potassium concentrations in current-year leaves and branches of Pinus densiflora (naturally regenerated saplings), Cryptomeria japonica (planted saplings) and Quercus serrata (planted saplings and coppice shoots) in Fukushima, Japan. We collected current-year shoots from 10 individuals of each species over two growing seasons at intervals of 1–4 months, between June 2016 and December 2017. For the deciduous species Q. serrata, we also collected dead leaves that remained attached to branches in December to investigate reabsorption of ¹³⁷Cs. All collected shoots were divided into leaves and branches, oven-dried, and ground; dry weights of each sample were recorded. ¹³⁷Cs activity concentrations were measured using a germanium semiconductor detector. Potassium concentrations were quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). Increases in dry weight were observed in both leaves and branches between May/June and August; growth then slowed considerably and virtually ceased after October. Clear seasonal changes in ¹³⁷Cs activity concentrations were observed in both 2016 and 2017, regardless of tree species. Concentrations were higher in young leaves and branches during May and June, then decreased and changed relatively little from August to winter. Reduced ¹³⁷Cs activity concentrations in dead leaves of Q. serrata were observed only in December 2017 (approximately 15% lower than in October). This reduction may indicate reabsorption of ¹³⁷Cs in leaves prior to shedding. The changes in potassium concentrations were similar to those in ¹³⁷Cs in both years. Potassium concentrations were higher in young leaves than in mature leaf and branch samples collected later in the year. A reduction of about 50% in the potassium concentrations in dead leaves of Q. serrata was also observed in December. A positive relationship between ¹³⁷Cs and potassium concentrations in leaves and branches was observed in all species, except for planted Q. serrata. This relationship may indicate that ¹³⁷Cs moves in tree shoots with potassium. Leaf and branch weight correlated negatively with ¹³⁷Cs and potassium concentrations. Reduced concentrations may indicate dilution of these elements as a result of biomass increases over the growing season. Our results imply that irrespective of species, ¹³⁷Cs exhibits seasonal variations resulting from dilution; these variations correspond with trends in potassium, with higher levels in young organs and decreased levels in older organs.

我们研究了日本福岛的当年松（天然再生树苗），日本柳杉（种植的树苗）和锯齿栎（种植的树苗和小灌木林枝）的当年叶片和枝中的放射性铯（¹³⁷ Cs）活性和钾浓度的季节性变化。。我们收集了当年的芽从每个品种的10个人在两个生长季节在1-4个月的时间间隔，2016年6月和2017年十二月间为落叶树种Q。在锯缘青蟹中，我们还收集了12月仍然附着在树枝上的枯叶，以研究^137种植物的重吸收。Cs。收集的所有嫩芽均分为叶子和树枝，烘干并磨碎。记录每个样品的干重。使用锗半导体检测器测量了¹³⁷ Cs的活性浓度。使用感应耦合等离子体发射光谱法（ICP-OES）对钾浓度进行定量。在5月/ 6月至8月之间，叶片和树枝的干重均增加了。然后增长显着放缓，并在10月之后几乎停止了增长。无论树种如何，2016年和2017年均观察到¹³⁷ Cs活性浓度的明显季节性变化。在5月和6月，嫩叶和树枝中的浓度较高，然后从8月到冬季下降并且变化相对较小。减少¹³⁷Q枯叶中Cs的活性浓度。仅在2017年12月才观察到锯齿状（比10月低约15％）。这种降低可能表明脱落前叶片中¹³⁷ Cs的重吸收。两年中钾浓度的变化与¹³⁷ Cs中的变化相似。幼叶中钾的浓度高于今年晚些时候收集的成熟叶和分支样品中的钾浓度。将Q的死叶中的钾浓度降低约50％。在12月也观察到锯齿状。¹³⁷之间的正向关系除种植的Q以外，所有物种的叶子和树枝中的Cs和钾浓度均得到观察。锯齿状。这种关系可能表明有¹³⁷ Cs的钾在树苗中移动。叶片和树枝的重量与¹³⁷ Cs和钾浓度呈负相关。浓度降低可能表明这些元素被稀释，这是由于生长期生物量增加所致。我们的结果表明，无论何种物种，¹³⁷ Cs都表现出由于稀释而引起的季节性变化；这些变化与钾的趋势相对应，年轻器官中的钾含量较高，而老器官中的钾含量下降。