ISSN 1067-4136, Russian Journal of Ecology, 2008, Vol. 39, No. 2, pp. 99–104. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © T.V. Denisova, K.Sh. Kazeev, 2008, published in Ekologiya, 2008, No. 2, pp. 110–115.
The number of the sources of ionizing radiation
affecting the biosphere is constantly increasing, and so
is the importance of research in radiobiology and radi-
ation ecology (Kudryashov, 2004).
Soil, one of the most important and indispensable
natural resources, ensures the stability of both individ-
ual biocenoses and the biosphere as a whole. Since the
role of soil microorganisms is of utmost importance, it
is generally believed that deterioration of microbial
communities may result in destruction of an entire eco-
system. Therefore, timely detection of the changes in
the soil microbiota that could cause negative effects
seems much more important than detection of alter-
ations of physical or chemical parameters of the soil.
Each group of microorganisms plays a speciﬁc and
multifaceted role in the life of soil. Many researchers
believe that the soil microbiota is very sensitive to
changes in soil conditions (Zvyagintsev, 1978; Dobro-
vol’skii et al., 1985;
…, 1988); therefore,
we may safely assume that microbiological parameters
are the most suitable for early diagnosis of industrial
deterioration of the pedosphere. It has been emphasized
that the lack of data on the radioecology of microorgan-
isms is a serious drawback in modern theoretical and
applied radioecology (
We estimated the effect of
irradiation at doses of 1,
5, 10, and 20 kGy on the numbers of the main groups of
ordinary chernozem soil microorganisms, including
ammoniﬁers, nitrogen-ﬁxing bacteria of the genus
, and micromycetes, and studied the time
course of the restoration of their numbers after
ation in model experiments by counting the microor-
ganisms after 3, 30, 90, and 180 days of incubation of
soil samples at a temperature and a moisture content
optimal for the biota.
MATERIALS AND METHODS
The object of the study was medium-deep, low-
humus, ordinary heavy loamy calcareous chernozem of
South European facies on yellow–brown loesslike
loams (Val’kov et al., 2002). The soil was sampled from
the arable layer (0–25 cm) at the Donskoi Training
Farm of the Don State Agrarian University (Ok-
tyabr’skii raion, Rostov oblast, Russia) in May 2003.
The humus content of the soil was 4.2%; the depth of
humus horizons A + AB was 78 cm (pH 7.8).
Freshly dried soil samples were irradiated with the
bremsstrahlung of a microtron (electron accelerator)
with an energy of 22 MeV and a beam current as strong
A. When the speciﬁed radiation dose had been
accumulated, the sample was removed from the beam.
The absorbed dose of
radiation was 1, 5, 10, or
20 kGy, depending on sample placement and the dura-
tion of exposure. The estimation error of the dose was
no greater than 10% (it was determined by variation of
the bremsstrahlung beam during irradiation). The addi-
tional radiation dose accounted for by induced radioac-
tivity of the samples was no higher than 10
days after irradiation, the dose rate of each sample
decreased to the background level. Unirradiated soil
samples served as a control. We estimated the numbers
of soil microorganisms in air-dried irradiated and con-
trol soil samples by the number of colony-forming units
(CFUs) of ammonifying bacteria growing on beef
Sensitivity of Some Groups of Ordinary Chernozem Soil
T. V. Denisova and K. Sh. Kazeev
Southern Federal University, ul. Bol’shaya Sadovaya 105, Rostov-on-Don 344006 Russia
Received April 4, 2006
—The effect of
irradiation at doses of 1, 5, 10, and 20 kGy on the microﬂora of ordinary chernozem
soil has been studied. The time course of the restoration of the microorganism numbers over 180 days after
irradiation has been studied in model experiments. The microorganism radioresistance decreases in the follow-
ing order: amylolytic bacteria >
> spore-forming bacteria > ammoniﬁers > micromycetes. A dose
of 20 kGy has a 96% suppressing effect on all microorganisms. Model experiments on the restoration of the
irradiated soil microﬂora have revealed different rates of increase in the numbers of microorganism groups
depending on the dose and incubation time.
radiation, soil microﬂora, ordinary chernozem, resistance, radiosensitivity.