It was also found that presowing treatment of wheat seeds by bacteria may result in significant variations in uptake of different elements and their translocation from roots to leaves. Concentrations of many elements in roots and leaves of the plants treated by bacteria were much higher than those in the control plants. In particular, concentrations of Cr, Rb, Ag, Sb, Cs, Hf, Th, and U increased in roots and in leaves of the wheat seedlings treated with Cellulomonas compared with those in the control. Figure 28.11 illustrates such variations in the example of three elements: Hf, Th, and U. On the other hand, concentrations of many rare earth elements (La, Ce, Sm, Yb, and Lu) and

FIGURE 28.12 Thorium in roots and leaves of wheat seedlings noninfected (a) and infected (b) with Mycobacterium.

FIGURE 28.12 Thorium in roots and leaves of wheat seedlings noninfected (a) and infected (b) with Mycobacterium.

Fe increased only in roots, and contents of K, Sc, Zn, and Eu were higher only in leaves, of the plants treated by the bacteria.

Similar variations in element uptake were observed after treatment of seeds with Mycobacterium. Figure 28.12 shows concentrations of Th in roots and leaves of wheat (Triticum astevum) infected and non-infected with Mycobacterium. The differences in Th uptake by treated and nontreated with Mycobacterium plants are statistically significant. Figure 28.13 illustrates the dynamics of Th in soil artificially contaminated with this metal after growth in the soil wheat seedlings inoculated with Mycobacterium.

It is known that, because of their high complexing ability, all radionuclides can be bound tightly to solid surfaces [131]. Therefore, one might expect that an addition of Th to the experimental soil may result in a quite rapid absorption of Th by soil organic matter and Th adsorption on the surface of soil particles. The observed variations in Th content in the soil might be caused solely by physiological activity of the experimental plants and microorganisms. Thus, it may be assumed that the changes in species diversity in the rhizosphere and, as a result, variations in the organic exudates into the soil can stimulate transfer of certain elements to more bioavailable forms. As a consequence, roots will be able to take up more metals and the rate of metal translocation to leaves may also be increased.

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