Radiocesium concentration in seeds of Japanese fir (Abies firma Sieb. et Zucc.) growing in Fukushima forests 4.5 years after the Fukushima Daiichi Nuclear Power Plant accident

Seed soundness is of paramount importance for all plants. Seed soundness of forest trees might have been negatively affected after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, when a massive amount of artificial radionuclides deposited on forest areas. However, information on seeds of forest tree species contaminated with radionuclides is limited because they are rarely encountered in forest ecosystems. Japanese fir (Abies firma Sieb. et Zucc.) is a predominant tree in natural secondary forests in the Abukuma Mountains in Fukushima, and this species shows masting; cone production occurs every 2 or 3 years, meaning that the contamination levels of A. firma seeds remain unknown. We investigated the contamination levels of Cs-137 in cone components (seeds, wings and cone scales) of A. firma approximately 4.5 years after the FDNPP accident. The Cs-137 concentration in seeds showed the lowest contamination level of the three cone components. In addition, there was a difference in Cs-137 concentration between seeds and cone scales, suggesting a difference in Cs-137 contamination levels between strict seed feeders and seed-cone feeders. Our results indicate that the combination of observed low contamination levels of seeds of A. firma and expected small root uptake of Cs-137 from soil might lead to low contamination levels of Cs-137 in recruits of this species.