Changes in cesium distribution in field-grown rice plants throughout the cultivation period

Purpose Cs is absorbed by plants via the roots and is then distributed to different plant parts. In pot experiments with rice, Cs concentration in the above-ground parts changed dramatically from the heading stage until maturation. The aim of this study was to clarify the dynamics of Cs distribution in field-grown rice plants throughout the cultivation period. Methods Field experiment was conducted using Indica cultivar ‘Habataki’ (higher Cs accumulation) and Japonica cultivar ‘Koshihikari’ (lower Cs accumulation) under different K application levels for 2 years. Changes in Cs and K concentration in each plant part and exchangeable Cs and K concentrations in soil were analyzed throughout the cultivation. Laser ablation-inductively coupled mass spectrometry was conducted to reveal tissue-specific accumulation of Cs and K in internodes. Results Cs concentrations in each part were at similar levels in the heading stage irrespective of the cultivars but greatly changed toward the maturation stage. Particularly, Cs concentration in internodes showed the largest increase. Cs accumulated to the same level in the large vascular bundles and parenchyma in the internodes. Habataki displayed a higher accumulation level of Cs in the internodes and distribution ratio of Cs to brown rice than Koshihikari. The effect of K application on Cs distribution was lower than that in the previous pot experiment. Conclusions Cs accumulation in the internode tissues, along with its distribution to brown rice, was greatly increased during ripening period in field conditions. Habataki showed higher Cs accumulation in internode and distribution ratio to brown rice than Koshihikari.