Effect of mycorrhizal infection on root uptake by pine seedlings and redistribution of three contrasting radio-isotopes: 85Sr, 95mTc and 137Cs

Mycorrhizal infection is known to improve phosphate nutrition and water supply of higher plants. It has been reported to both increase the uptake of potentially toxic pollutant elements and to protect plants against toxic effects. Little is known about the effect of mycorrhizal infection on the dynamics of radioactive pollutants in soil-plant systems. The aim of this study was to compare the root uptake and root-shoot transfer of three radio-isotopes with contrasting chemical properties (85Sr, 95mTc and 137Cs) in mycorrhizal and control, non mycorrhizal plants. The plant studied was Pinus pinaster and the associated ecto-mycorrhizal fungus was Rhizopogon roseolus (strain R18-2). Plants were grown under anoxic conditions for 3 months then transferred to thin layers of autoclaved soil and allowed to grow for four months. After this period, the rhizotrons were dismantled, and plant tissue analysed. Biomass, nutrient content (K, P, N, Ca) and activities of each isotope in roots, shoots and stems were measured, and the degree of mycorrhizal infection assessed. The transfer factors decreased in the order Tc>Sr>Cs as expected from the degree of immobilisation by soil. No effect of mycorrhizal infection on root uptake was observed for Sr. Shoot activity concentration of Tc was decreased by mycorrhizal infection but root uptake correlated well with mycelial soil surface area. In contrast, Cs shoot activity was greater in mycorrhizal than control plants. The uptake and root to shoot distribution shall be discussed in relation to nutrient dynamics. (author)