Growth and uptake of caesium, rubidium, and potassium by ectomycorrhizal and saprotrophic fungi grown on either ammonium or nitrate as the N source

Abstract

After the accident at the Fukushima Dai-ichi Nuclear Power Plant in 2011, high activities of radiocaesium have been reported in wild mushrooms in Japan. Fungi play an important role in the dynamics of radiocaesium in forest ecosystems. We examined the contents of caesium (Cs), rubidium (Rb), and potassium (K) in the mycelium of 15 isolates of ectomycorrhizal (EM) fungi and nine isolates of saprotrophic (SA) fungi in a synthetic medium with either ammonium chloride (NH4Cl) or sodium nitrate (NaNO3), supplemented with 1 ppm caesium chloride and rubidium chloride. The mycelia were harvested after 8 weeks of incubation, and the contents of Cs, Rb, and K were measured by inductively coupled plasma mass spectrometry. The dry weight of the mycelium in the medium with NH4 was significantly higher than that with NO3, although some EM species, Hebeloma, Astraeus, Scleroderma, and Pisolithus, grew well in the medium with NO3. Among SA species, Crucibulum and Cyathus grew in the medium with NO3. The uptakes of Cs, Rb, and K by Suillus, Pisolithus, and Rhizopogon were higher than that in other EM and SA species when they grew on the medium with NH4, while the uptakes of these elements by Astraeus and Scleroderma were higher than those by other species grown on the medium with NO3. The content of Rb was positively correlated with Cs (r = 0.85, p < 0.001) and K (r = 0.51, p < 0.001). The accumulation of Cs, Rb, and K was differently affected by the N source and fungal species.