In a greenhouse experiment, some features of Tritium migration from an aqueous feeding solution to white willow (Salix alba L.) habitat components and isotopic effects of hydrogen during the willow growth have been studied. A number of rate constants for tritiated water diffusion through pores, cell membranes and uptake through the root system (k = (8.44±0.03)•10-7 s-1); 3 H/ 1 H isotopic exchange in OH-groups of organic substances (k = 5.07•10-7); "isotopic lightening" during photosynthesis (k = 5.00•10-8) were calculated from the experimental data. The rate constant of tritium transfer through the root system to intercellular sap of plants is 2.17±1.45•10-6 s-1. The tritium distribution between the feeding solution and the intercellular sap has come to equilibrium within 1-2 weeks. The fractionation factor (α) is 0.88-0.94 and does not depend on the concentration of 3 H in the feeding solution. The rate constant of transformation of tritium into organically bound species is 8.6±3.0•10-7 s-1. The equilibrium has set from 4 to 11 weeks, α = 0.17-0.19 and does not depend on 3 H concentration in the feeding solution. At the same time, strong isotopic effect of "lightening" of the feeding solution, probably owing to transpiration, has been observed. The rate constant value of Tritium transpiration calculated from the experimental data is 2.67±0.27•10-8 s-1. The rate of tritium removal due to transpiration is proportional to its concentration in the feeding solution. The factor of tritium fractionation during transpiration is 1.35±0.08.

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The paper is devoted to the study of the kinetics of tritium redistribution between living and inanimate matter of white willow in the “greenhouse” experiments. It was shown that the concentration of tritium in the aquatic environment significantly affects the kinetic parameters of its assimilation in the organic and inorganic matter of the organism of the white willow (Salix alba L.). The kinetics of the influx of tritium from the aqueous nutrient into the intracellular juice, the organic phase of plants, and transpiration fumes, depending on the concentration of the superheavy hydrogen isotope, are described. Dose-dependent effects were identified, accompanied by fractionation of hydrogen isotopes in all components of the biosystem - the aquatic food environment, intracellular juice, transpiration fumes, and in the organic phase. It was found that with an increase of the initial specific activity of aqueous feeding solution (by 8.6 times): the rate of tritium removal from it and from intracellular juice increases (by 14.8 and 15.6 times, respectively), the degree of assimilation of this isotope into intracellular juice decreases (by 41.3 times), and its the part that enters the organic phase of wood (1.3 times) decreases the relative proportion of tritium in transpiration water (5.7 times). The existence of physiological barriers that sharply and significantly limit the assimilation of tritium into the components of the willow has been proved. Thus, the value of the barrier during the migration of this isotope of hydrogen into the intracellular juice reaches 15 % and only 18 - 25 % of tritium gets from the external water into the organic phase.

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