ИСТИНА

Analogies and differences between Cs-137 and stable K (K-39) bioavailability for crops growing on radioactively contaminated lands are still under discussion. To clarify the peculiarities of Cs-137 and K root uptake and the elements distribution over the parts of plant biomass the field observations within post-Chernobyl Plavsky radioactive hot spot (Tula region, Russia) have been examined. Total Cs-137 and non-exchangeable K were analyzed in soils that resulting in comparability of their bioavailability for plants. 4 agricultural crops of field rotation (spring barley, maize, potatoes, and rape) and semi-natural vegetation of dry and wet meadows were selected for the study. Above- and belowground parts of biomass were separated for the detailed examination. To avoid the difference in Cs-137 and K content in soils of different plots and to appreciate the biological peculiarities of individual crops the transfer factor (TF) values (the ratio of the activities for Cs-137 and concentrations for K between vegetation and in soil) were calculated. Determined current activities of Cs-137 in arable and native chernozems of the area taking into account initial level of contamination and the relief position varied from 450 Bq/kg to 700 Bq/kg (170-280 kBq/m2). The amount of non-exchangeable K in rhizosphere represented 0.09-0.14% without mineral fertilizers and 0.40% after soil fertilization (for maize). Root uptake of the elements was characterized by different peculiarities. As a whole TFK were several orders more than TFCs-137 that stressed the biogenic nature of potassium and the xenophobic nature of caesium. Among the investigated agricultural crops and meadow plant communities TFK were minimal for maize and barley (5.1-5.7), middle – for rape, and dry and wet meadows (6.5-7.2), and maximal – for potatoes (17.4). TFCs-137 were minimal for rape (0.01), middle – for wheat, barley and potatoes (0.05-0.06), and maximal – for maize, dry and wet meadows (0.11-0.19). An accounting of Cs-137 and stable K distribution among above- and belowground parts of plant biomass clearly demonstrated the importance of biological characteristics in root uptake of the elements: wheat, barley and maize (Gramíneae family) were characterized by elevated Cs-137 activities in belowground parts (12-14 times higher than in shoots), and rape (Brassicaceae family) and potatoes (Solanaceae family) were characterized by homogenous distribution of the radionuclide over plant biomass, whereas K concentrations in aboveground parts of plants were 1.5-10 times greater than in belowground parts of plants for all investigated crops. Thus, Cs-137 and stable K were difficult if not impossible to consider as biochemical analogists in root uptake from radioactively contaminated soils. The study was conducted with the support from the Russian Foundation for Basic Research (project no. 14-05-00903).