Effect of soil exchangeable potassium content on cesium absorption and partitioning in buckwheat grown in a radioactive cesium-contaminated field

Abstract

The effect of soil exchangeable (plant-available) potassium (ExK) content on cesium (Cs) absorption and translocation in buckwheat was evaluated in a field contaminated with radioactive Cs (¹³⁴Cs and ¹³⁷Cs, RCs) in 2013. The RCs concentration in buckwheat was significantly positively correlated with the naturally occurring stable Cs (¹³³Cs, SCs) concentration, and was lower at higher soil ExK content. The RCs and SCs were actively absorbed by buckwheat until the flowering stage. The soil ExK content was significantly negatively correlated with soil exchangeable RCs and SCs (ExRCs and ExSCs) concentrations. Greater RCs and SCs absorption by buckwheat in soils with low ExK contents was mainly due to higher soil ExRCs and ExSCs concentrations. Reproductive organs showed the largest differences in SCs concentration between low-ExK and high-ExK plots. The root–shoot and shoot–reproductive organs translocations of SCs markedly decreased with increasing soil ExK content. In the root–shoot and shoot–reproductive organs translocations, the discrimination of SCs and K decreased with decreasing soil ExK content. Our main findings were as follows: (1) because RCs are mainly taken up at the earlier growth stage, potassium should be applied as a basal fertilizer to decrease the RCs concentration in buckwheat; (2) lower soil ExK content led to higher soil ExRCs concentrations, resulting in greater RCs absorption by buckwheat; (3) the high Cs absorption and translocation and weaker discrimination between Cs and K in low ExK content soil may be due to the expression of K transporter(s) with weak discrimination between Cs and K.

Keywords:

• Cs accumulation
• discrimination
• Fagopyrum esculentum Moench
• Fukushima
• radionuclide

Classification:

• Crop Physiology

Acknowledgments

We thank Mr Yoshihiro Yashima, a farmer in Date, Fukushima, for his cooperation during these experiments. We thank the following staff at the Agricultural Radiation Research Center, NARO Tohoku Agricultural Research Center: Dr Hisaya Matsunami and Mr Yoshihiko Takahashi for their assistance with ¹³⁴Cs and ¹³⁷Cs analyses; Dr Tetsuya Eguchi for assistance with the soil ExK analysis; and Ms Yuki Sato, Ms Tomoko Saito, Ms Yukari Watanabe, Ms Michie Mimori, and Ms Yurie Yoshida for sample preparation. We also thank Mr Kazutoshi Gondo (Kurume Research Park Co., Ltd.) for his support in the ICP-MS analyses.