Аннотация:Root uptake and translocation of 137Cs from soil to plant is the key for estimation of general ecological situation and land use on radioactive contaminated territories. There are numerous researches concerning the relationship between the level of the radionuclide presence in soils and its accumulation in vegetation that usually describes as transfer factor (TF) for 137Cs (the ratio of the specific 137Cs activity in the plant tissue and the soil). But in most cases only edible organs or above-ground parts of plants are taken into account in evaluating TF. It is reasonable from the standpoint of practical use, but does not provide accurate information in the study of 137Cs biogeochemical cycle features.
The study of the 137Cs root uptake from the radioactive contaminated chernozem soil and its distribution between above-ground and below-ground fractions of grass vegetation was conducted in the natural conditions on the territory of Plavsk radioactive spot (Tula region, Russia) ~25 years after Chernobyl accident. The main crops of field rotation in this landscape (wheat, barley, potatoes, rape, maize) which occupy watersheds and slopes with arable chernozems contaminated at a level 460-670 Bq/kg (170-220 kBq/m2) and natural grassland ecosystems which occupy lower parts of slopes and floodplains with dry and wet meadows contaminated at a level 620-710 Bq/kg (210-250 kBq/m2) were examined.
Total accumulation of 137Cs in vegetation strongly depends on the level of soil radioactive contamination (correlation coefficient 0.87). So specific 137Cs activity in vegetation of meadows (103-160 Bq/kg) in general more than one in agricultural crops (9-92 Bq/kg). Other reason may be the predominance of perennial herbs in natural meadows whereas agricultural systems contain annual crops.
The values of 137Cs TF in the studied ecosystems vary within a relatively narrow range: from 0.01 (rape) to 0.20 (wet meadow), that confirms the discrimination of the radionuclide root uptake. At the same time the distribution of 137Cs between above-ground and below-ground fractions of plants in all observed cases is quite nonuniformly: below-ground parts of vegetation accumulate 3-5 times more than above-ground ones. An exception is potatoes agrocenosis where the TF values for different parts are almost identical, but below-ground fraction of potatoes consists of grater modified shoots, but no roots. There is a pronounceable difference in 137Cs TF values for root tissues of various plant associations. The highest TF values in below-ground fraction are typical for vegetation with agricultural or wild cereals (0.15-0.26) having fibrous root system, the lowest TF values are characterized for rape agrocenosis (0.02) having stem root system. Thus, the major differences in the 137Cs TF from contaminated soil to plant may be closely related to the features of the root system and the further translocation of the radionuclide into shoot, which requires quantitative account of 137Cs accumulation not only in above-ground green parts, but also in roots.
The study was conducted under financial support by the Russian Foundation of Basic Research (RFBR), project no. 14-05-00903A.