Relationship between the activity concentration of 137Cs in the growing shoots of Quercus serrata and soil 137Cs, exchangeable cations, and pH in Fukushima, Japan

Incorporation of radiocesium by plants via root uptake appears to be affected by some of the exchangeable cations in the soil and/or pH of the soil. However, few studies have examined the relationship between Cs-137 in trees and soil properties in the area surrounding the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the accident in March 2011. To elucidate the relationships between the root uptake of Cs-137 by deciduous broadleaved trees and soil properties, we measured the activity concentration of Cs-137 in the growing shoots of coppiced konara oak (Quercus serrata) grown after the FDNPP accident and the amounts of total Cs-137; exchangeable (ex-) Cs-137, ex-K, ex-Mg, and ex-Ca; and pH (H2O) in soils collected from 34 forest stands in Fukushima between December 2016 and May 2017. Ex-Cs-137 showed a positive linear relationship with the activity concentration of Cs-137 in the growing konara oak shoots, whereas ln-transformed ex-K, ex-Mg, ex-Ca, and pH (H2O) showed negative linear relationships with ln-transformed Cs-137 activity concentrations in the growing shoots. However, only ex-Cs-137 and ex-K were identified as significant factors determining the activity concentration of Cs-137 in konara oak according to multiple regression methods and a model selection using Akaike information criterion; ex-K had a stronger influence on the activity concentration of Cs-137 in konara oak than ex-Cs-137. In the present study, we demonstrated that soil ex-K negatively and non-linearly alters Cs-137 activity concentration in deciduous broadleaved trees. We also noted that the relationship between Cs-137 in deciduous broadleaved trees and soil ex-K in forests without K fertilization was similar to the relationships between Cs-137 in other plants and ex-K in K-fertilized lands reported in previous studies of the FDNPP accident.