ABSTRACT Radiocesium (RCs) discharged by the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Co., Inc.) accident has extensively contaminated agricultural land in Fukushima Prefecture and its neighboring areas. Many studies have demonstrated that Cs (RCs and 133Cs) uptake of plants is affected by the exchangeable K (Ex-K) concentration in soil. However, the precise plant–soil interaction in relation to Cs uptake is still unclear. The aim of this study was to investigate Cs uptake of plant in field by focusing on xylem exudate and roots because nutrients in xylem exudate reflect medium (soil) conditions and affect nutrient accumulation in shoots. Two varieties of amaranth, K4 (Amaranthus caudatus L.) and Mexico type (A. hypochondriacus L.), which have different Cs uptake abilities, were grown in four fields and in pots (750 to 3440 Bq kg−1 of RCs) in Fukushima Prefecture. Cs concentrations in xylem exudate, shoot, and soil; Ex-K concentration in soil; and root distribution in soil were determined. RCs concentration in xylem exudate varied from 0.04 to 164 Bq kg−1 and 133Cs concentration in xylem exudate ranged from 0.01 to 33.7 μg kg−1. The Cs concentrations were decreased by the high Ex-K concentration and the large amount of 2:1 type clay minerals in soil. The average of the ratios of Cs concentration in shoot to Cs concentration in xylem exudate for all samples was 127 ± 112 (mean ± standard deviation), although no clear correlation was found between them. The correlations betwee\n RCs and 133Cs concentrations in xylem exudate and shoot were strong in pot and in the field with low Ex-K concentration. Eighty-five percent of the total root length was distributed in the topsoil (0–20 cm soil layer). The positions where roots take up Cs were estimated from the differences in the vertical distribution of RCs and 133Cs concentrations in soil. The estimated Cs uptake ratios of topsoil to total soil layer ranged from 7% to 91% and varied with the concentration and the vertical distribution of Ex-K in soil.

中文翻译：

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福岛田间苋属植物对铯的吸收，重点关注木质部渗出液中的 Cs 浓度和根分布

摘要福岛第一核电站（东京电力公司）事故排放的放射性铯（RCs）已广泛污染了福岛县及其周边地区的农田。许多研究表明，植物对 Cs（RCs 和 133Cs）的吸收受土壤中可交换钾 (Ex-K) 浓度的影响。然而，与 Cs 吸收相关的精确植物 - 土壤相互作用仍不清楚。本研究的目的是通过关注木质部渗出液和根部来研究田间植物对 Cs 的吸收，因为木质部渗出液中的养分反映介质（土壤）条件并影响芽中养分的积累。两种苋菜品种，K4（Amaranthus caudatus L.）和墨西哥型（A. hypochondriacus L.），具有不同的Cs吸收能力，在福岛县的四个田地和盆中（750 至 3440 Bq kg−1 的 RCs）种植。木质部渗出液、枝条和土壤中的 Cs 浓度；土壤中的 Ex-K 浓度；并确定根在土壤中的分布。木质部渗出液中的 RCs 浓度范围为 0.04 至 164 Bq kg-1，木质部渗出液中的 133Cs 浓度范围为 0.01 至 33.7 μg kg-1。土壤中高 Ex-K 浓度和大量 2:1 型粘土矿物降低了 Cs 浓度。所有样品的枝条中的 Cs 浓度与木质部渗出液中的 Cs 浓度之比的平均值为 127 ± 112（平均值 ± 标准偏差），尽管在它们之间没有发现明显的相关性。木质部渗出液和芽中 RCs 和 133Cs 浓度之间的相关性在盆栽和 Ex-K 浓度较低的田间很强。总根长的 85% 分布在表土（0-20 厘米土层）中。根据土壤中RCs和133Cs浓度垂直分布的差异估计根吸收Cs的位置。表层土壤对总土壤层的 Cs 吸收率估计为 7% 至 91%，并随土壤中 Ex-K 的浓度和垂直分布而变化。