Analysis of Local Dandelion (Taraxacum officinales.l.) Cenopopulations from Radioactively Contaminated Zones

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  • 1067-4136/01/3202- $25.00 2001

    MAIK Nauka

    /Interperiodica0102

    Russian Journal of Ecology, Vol. 32, No. 2, 2001, pp. 102109. Translated from Ekologiya, No. 2, 2001, pp. 117124.Original Russian Text Copyright 2001 by Pozolotina.

    Radionuclide migration in biogeocenoses and thebiological effects of ionizing radiation on organismsand their communities are often difficult to studybecause radioactive contamination of landscapes isnonuniform. Radionuclides falling from the atmo-sphere and deposited by water flows are distributedunevenly; the strength of their fixation in the soil and,therefore, their availability to plants strongly vary;hence, the range of radiation loads within contaminatedareas may be broad (Tikhomirov, 1972; Aleksakhin,1982). In natural ecosystems, it is impossible to takeinto account the entire complex of environmental con-ditions and differentiate between the effects of individ-ual factors. Experimental radiobiologists have accumu-lated vast data on the effects of radiation on individualcells and plants. These data are very important butinsufficient for understanding the processes occurringat the population level (Grodzinskii, 1989). The struc-tural and functional hierarchy of living organismsimplies the existence of a multilevel system ofresponses to external influences. Therefore, the com-prehensive analysis of such a systemic phenomenon asthe adaptive response to irradiation at different levels,from individual cells to cenopopulations, should beperformed with great caution (Reimers, 1994).

    The purpose of this work was to study the responseof plants to chronic low-dose irradiation in dandelion(

    Taraxacum officinale

    s.l.) populations growing in theareas of the Eastern Ural Radioactive Trace (EURT)and the Techa River floodplain, which were contami-nated by radioactive discharge from the Mayak Produc-tion Association.

    MATERIALS AND METHODSThe samples of soils, vegetative plant parts, and

    seeds were taken along the central EURT axis and inthe Techa River floodplain near the village of Brodokal-mak in 1998. The background plot was located beyondthe zone of radioactive contamination. The soils weresampled by 5-cm layers to a depth of 30 cm, taking intoaccount the sample area. Samples of the abovegrounddandelion phytomass were taken from the sites adjoin-ing the soil section. In addition, seeds of 1020 individ-ual plants of each cenopopulation were collected. Soilsamples were dried and sifted through a screen (meshsize 0.1 cm); phytomass samples were incinerated. Thecontent of

    137

    Cs

    was measured in a Canberra Packardgamma-spectrometer with a germanium sensor;

    90

    Sr

    was determined radiochemically by conventional meth-ods (

    Metodicheskie rekommendatsii

    , 1980).

    Taraxacum officinale

    s.l., a widespread polycarpicspecies of the family Asteraceae, is convenient for indi-cating biological effects in technogenically disturbedecosystems. Both vegetative reproduction by root suck-ers and seed reproduction are observed. Most authorsindicate that seeds are formed parthenogeneticallywithout chromosome reduction and pseudogamy (Pod-dubnaya-Arnoldi, 1976; Ermakova, 1990). The dande-lion populations studied, growing in contaminatedareas for a long time, have been exposed to theincreased background radiation over several dozens ofgenerations.

    The effect of chronic irradiation at the cell level wasdetermined by analyzing chromosome aberrations in

    Analysis of Local Dandelion (

    Taraxacum officinale

    s.l.) Cenopopulations from Radioactively Contaminated Zones

    V. N. Pozolotina

    Institute of Plant and Animal Ecology, Ural Division, Russian Academy of Sciences, ul. Vosmogo Marta 202, Yekaterinburg, 620219 Russia

    Received June 16, 2000

    Abstract

    Local dandelion (

    Taraxacum officinale

    s.l.) populations were studied in the areas of the EasternUral Radioactive Trace and the floodplain of the Techa River in its upper reaches. In impact plots, the densityof soil and plant cover contamination with

    90

    Sr and

    137

    Cs exceeded the background level by factors of 13440and 2500, respectively; the radiation load exceeded the background level by factors of 1.5 to 45. The seedprogeny of plants from these plots was characterized by a high proportion of abnormal seedlings and anincreased level of chromosome aberrations in meristem cells. In some years, variation in the seedling viability,growth rate, and developmental rate in these plots exceeded the reaction norm of plants from the backgroundplot, demonstrating both stimulation and inhibition of growth processes. The response of seeds to acute irradi-ation at high challenging doses varied depending on the level of background radiation in the plots.

    Key words

    : radioactive contamination, small doses,

    Taraxacum officinale

    s.l., chromosome aberrations, radi-osensitivity, intraspecific variation.

  • RUSSIAN JOURNAL OF ECOLOGY

    Vol. 32

    No. 2

    2001

    ANALYSIS OF LOCAL DANDELION 103

    anaphase root meristem cells of

    1

    seed progeny. Prep-arations for cytogenetic analysis were made by thesquash method and stained with acetoorcein. In eachvariant, 5001500 anaphases in 1225 rootlets wereanalyzed.

    The effects at the ontogenetic and population levelswere estimated by analyzing individual seed progeniesof ten plants from each cenopopulation. Seeds germi-nated in paper rolls, and experiments were performedin five replications. Viability was estimated from theseed vigor and germination rate, survival of one-monthseedlings, and the rates of leaf formation and rootgrowth. The proportions of abnormal seedlings in eachfamily and the entire sample were determined. Thesedata allowed the assessment of both individual varia-tion of all these parameters within each sample andvariation within individual families (with respect toroot growth and the proportion of abnormal plants). Inmaternal plants, the numbers of leaves and flower stalksand the size of the largest leaf were determined.

    At the next stage, the adaptive potentials of the seedprogenies formed under different radiation conditionswere studied. Seeds were gamma-irradiated at doses of100 and 250 Gy (dose rate 15.5 cGy/s) in an Issledova-tel-type unit. Plant tolerance for challenging irradia-tion was estimated by the aforementioned combinationof criteria. The results obtained at each stage ofresearch were processed statistically using the standardSTATISTICA for Windows software package.

    RESULTS AND DISCUSSION

    Radioecological characteristics of test plots.

    Ear-lier, we performed detailed studies on the levels ofradioactive contamination in the Ural region. Theirresults demonstrated that the soils contained techno-genic radionuclides of various origins. The contribu-tions of

    90

    Sr,

    137

    Cs

    , and the transuranium elements dis-charged during the Kyshtym accident (1957) and ofradioactive elements transferred by wind from theshores of Lake Karachai (1967) were estimated qualita-tively (Aarkrog

    et al.

    , 1997, 1998). The floodplain eco-systems of the Techa River, in which radioactive wastefrom the Mayak works was dumped between 1949 and1951, are still heavily contaminated throughout theriver course (Trapeznikov

    et al.

    , 1999).This paper deals with the results of studies in four

    impact plots (two located on the EURT central axis andthe other two, in the Techa River floodplain) and onebackground plot in Beloyarskii raion, beyond the con-taminated zone. The background plot 1 was in thePyshma River floodplain, and its thick ground vegeta-tion was represented by a herbgrass community. Plot2 was in a narrow floodplain area near the Bagaryak Riverchannel. Thick ground vegetation (coverage 9095%)was represented by a community of herbs, annualgrasses, and bluegrass. Plot 3 was located 400 m awayfrom Lake Tygish, in a birch forest outlier with a

    thinned grass cover growing on gray forest soil. Plots 4and 5 were in the Techa floodplain, on gently slopingbanks near the river channel. Ground vegetation con-sisted of several layers with 100% coverage and wasrepresented by a herbgrass community growing onstratified alluvial soils. The comparison of plotsshowed that the densities of their contamination with

    90

    Sr and

    137

    Cs differ by factors of 13440 and 2500,respectively (Table 1).

    Studies on the distribution of radionuclides acrossthe soil profile in the EURT zone showed that the sur-face soil layer (010 cm) accumulates up to 90% oftheir total amount (Aarkrog

    et al.

    , 1997). The complexrelief and specific hydrologic conditions of floodplainlandscapes determine the specific behavior of radionu-clides in their soils and plant cover. Due to regular inun-dation during floods and the inflow of geochemicalmaterial from the catchment area and the river proper,floodplains accumulate large amounts of chemical sub-stances. As a rule, the contents of radionuclides in thesoil profile exponentially decrease with depth, butdeeper soil layers sometimes contain them in fairlylarge amounts (Trapeznikov

    et al.

    ,

    1999).Data on the contents of radionuclides in the phyto-

    mass and the root layer of the soil (020 cm) was usedfor calculating the coefficients of their biological absorp-tion (CBA) by the aboveground plant parts (Table 2).The analysis of the results showed that plants accumu-lated

    137

    Cs less actively than

    90

    Sr. This is explained bythe fact that, even in moist floodplain soils, the bulk of

    Table 1.

    Densities of soil and plant cover contaminationwith technogenic radionuclides in test plots, kBq/m

    2

    Plotnumber Location

    90

    Sr

    137

    Cs

    1 Background are