ИСТИНА

Caesium has been assumed as microelement with indeterminate significance in plant nutrition, but was beyond the main interests of specialists for a long. A different situation aroused with Cs-137 entering into environment after nuclear tests in the atmosphere and accidents at nuclear power plants when biogeochemical cycle of the radionuclide began to take on a new meaning due to its radioecological consequences. To gain greater insight into Cs-137 behavior in grassy ecosystems in comparison with main flux of mineral nutrients the field observations within post-Chernobyl landscape of Plavsky radioactive hot spot (Tula region, Russia) have been performed. The major cultures of crop rotation in chernozem region (wheat, spring barley, potatoes, soybean, amaranth, perennial grass mixture with galega and bromegrass) as well as semi-natural vegetation of dry and wet meadows were selected for the study. Above- and belowground parts of biomass were separated for examination of Cs-137 and mineral nutrients (ash elements) content. Current level of Cs-137 contamination of dominant arable chernozems of the area is 140-210 kBq/m2, in geochemically subjected alluvial soils it increases to 220-280 kBq/m2. To avoid the difference in Cs-137 content in soils of different plots the transfer factor (TF) values (the ratio of Cs-137 activities in vegetation and in soil) were calculated. It has been found that TF of Cs-137 in total biomass varied from 0.01-0.08 (galega, potatoes, soybean, amaranth, meadow herbs) to 0.15-0.32 (wheat, barley, meadow grasses) when ash elements content was in a range 5.2-16.4%. As this takes place, the order in which TFs and mineral nutrients content tend to rise is quite different: some crops with high content of ash elements are characterized by relatively low TFs of Cs-137 (potatoes, amaranth), and some crops with low ash content are characterized by relatively enlarged TFs of Cs-137 (wheat, barley). In sum, there is not any pronounceable correlation between Cs-137 and mineral nutrients in plants – correlation coefficient is not significant (-0.44). Moreover, given mineral nutrient distribution between aerial and belowground parts of vegetation is more or less homogeneous, when Cs-137 is deposed in roots of cultural and wild cereals. Commonly the portion of Cs-137 in ash elements of plants is negligibly small and falls between 2.10-12 and 1.10-11 % for dicotyledonous (minimal for galega) and between 1.10-11 and 5.10-11 % for monocotyledonous (maximal for wheat and barley). This is strengthened the case for significant discrimination of Cs-137 root uptake from contaminated soils. By this is meant that Cs-137 is not a neutral trace element consumed with total nutrients fluxes, but looks like ecotoxicant with reference to which plants are adopted on the basis of rhizofiltration anr rhizostabilisation strategy.