EFFECT OF ECTOMYCORRHIZAE AND AMMONIUM ON CS-134 AND SR-85 UPTAKE INTO PICEA-ABIES SEEDLINGS

Microorganisms play an important role in the fixation of radionuclides in forest soils, In particular, fungi have the capacity to absorb and translocate radionuclides. The role of the ectomycorrhizal fungus Heb eloma crustuliniforme in the uptake of radiocaesium (Cs-134) and radio strontium (Sr-85) into seedlings of Norway spruce (Picea abies) was in vestigated in a pouch test system. Inoculated and non-inoculated seedl ings; seedlings inoculated during 8 and 15 weeks; seedlings exposed du ring 2 and 3 weeks to the radioactive solution; and seedlings grown un der low and high ammonium conditions prior to the application of the r adionuclides were compared The final Cs-134 and Sr-85 activity was det ermined in fine-roots, main-roots, stems and needles. The results show ed that ectomycorrhizae reduced the uptake of Cs-134 and Sr-85. The de gree of ectomycorrhization was of crucial importance and seemed to be governed by the period during which ectomycorrhizae were allowed to de velop and by the ammonium concentration in the nutrient solution, The radionuclide uptake increased with increasing exposure time. Both radi onuclides were predominantly accumulated in fine-roots. However, needl es proved to describe best the result of net root uptake and transloca tion to the shoot. The uptake- and translocation-rates of Sr-85 were s maller than those of Cs-134. It is assumed that the translocation is c oupled with the intensity of water fluxes through the xylem and that S r-85 is more readily adsorbed into mycelium or plant tissue relative t o Cs-134. The effect of high ammonium growth conditions was overcome b y the effect of ectomycorrhization, except in needles with a very larg e biomass which behaved as a strong sink and led to a high accumulatio n of Cs-134. Copyright (C) 1996 Elsevier Science Ltd