Soil properties and K plant status affect Cs uptake by Lolium perenne
F. Giannakopoulou*, D. Gasparatos, I. Massas and C. Haidouti
Laboratory of Soils and Agricultural Chemistry, Agricultural University of Athens, 75 Iera Odos str., 11855,
*Corresponding author: E-mail: firstname.lastname@example.org, Tel. +30 210 5294090, Fax: +30 210
The effect of soil properties and K-status on plant tissues on Cs uptake in the shoots of Lolium perenne
plants was studied under greenhouse condition. The plants were grown on four different soil types,
contaminated with 40 mg kg-1 of Cs and sown at 60 and 420 days after contamination (treatments).
According to the results, significant variations on Cs uptake by Lolium perenne plants were observed among
different soil types and treatments, with clay content and ction exchange capacity to influence greatly Cs
uptake. Regardless to soil type or treatment, Cs concentration decreased, as K content increased in shoots in
both cuts of the plants, suggesting a direct competition between Cs+ and K+ ions during the process of
accumulation. Plants preferential uptake K+over Cs+ ions, as it seemed from the DF values that were
below unity in all treatments.
Keywords: cesium; potassium; soil; Lolium perenne plants; discrimination factor
Over the last decade, global warming became an environmental issue of great concern in scientific and
political forums. Trying to develop and exploit alternative power supply resources, with minimal carbon
dioxide emissions, nuclear energy appears attractive and friendly to the environment, but also controversial
in terms of the potential risk for radionuclides release in the ecosystem and the effective management of the
radioactive wastes. However, nuclear energy, with no CO2 emissions, could play an important role in the
global power supply system . On the other hand accidental and routine releases of radionuclides from the
nuclear energy are inevitable and can cause local, regional and even global contamination.
Cesium nuclides, considered as the most important artificial radionuclides produced by nuclear fission, due
to their high yield fission product, their long half-lives, their emissions of b and γ radiation decay and their
rapid incorporation into the biological systems. As plant uptake is the major pathway for migration of 137Cs
from soil to human diet, the knowledge of plant-related factors that control Cs uptake will be important for
devising effective strategies and developing techniques to minimize the transfer of Cs from soil to food chain
Stable Cs (133Cs), with identical to Cs radionuclides (137,134Cs) chemical behavior, has been used for
understanding the fate of radioactive Cs isotopes in various environmental systems . The properties of
stable Cs in different systems may be regarded as a useful tool in predicting the respective 137,134Cs bahavior
and their equilibrium distribution, and also provide a useful analogy for observing the variation of
radioactive Cs path in ecosystem . Recently, Salt et al.  concluded that the naturally occurring stable Cs
can be used as a reliable predictor of the bahavior of radiocesium in soil – plant systems. Therefore, to
facilitate experimental studies on radiocesium sorption, availability and mobility in the environment, the
utilization of stable Cs was often applied .
The mobility and fate of Cs in the soil to plant system is a function of processes occurring in the soil, since
soil solution acts as an intermediate environment between the solid phase and plant roots, and in the plants,
due to different physiological reactions for nutrient acquisition that are attributed to genotypic dissimilarities
. Among the soil properties there are certain soil parameters, such as clay content, CEC, clay mineralogy
Proceedings of the 3rd International CEMEPE & SECOTOX Conference
Skiathos, June 19-24, 2011, ISBN 978-960-6865-41-1
and potassium content that could diminish the mobility and availability of Cs to plants and thus its
assimilation by biota . The retention of Cs in soils is controlled by ion exchange at highly sorption sites in
the clay minerals that are especially located in the frayed edge sites of illite and in the hexagonal cavities of
vermiculite . Ions with physicochemical similarities with Cs, such as K, affect the selectivity of Cs
sorption by the solid phase of clay minerals and consequently Cs availability to plants .
The uptake of Cs has been studied in both soil and hydroponic experiments with special references to
potassium competition, as K is generally considered an effective inhibitor for Cs uptake by plant roots .
However most of these studies focused in the quantitative relationship between external K concentration and
Cs uptake by plants without taking into consideration the interaction between Cs+ and K+ ion in the root
uptake process and their accumulation within the tissues . Thus single correlations between Cs
concentration and soil properties are generally very weak and the applicability of these studies in natural
complex systems are not always reliable and capable to predict Cs transfer from soil to plant. The purpose of
this study was, therefore, to examine the factors affecting Cs uptake process by Lolium perenne plants, and
particularly the role of K, and the mechanisms involved, so as to interpret the way that K+ is related to Cs+
in soil-plant systems.
2. MATERIALS AND METHODS
To accomplish the aims of the present study, a completely randomized greenhouse pot experiment, in four
replicates, was conducted. Τhe plants were grown on four mineral soils with contrasting physicochemical
properties. Soil in each pot contaminated with 40 mg kg-1 of Cs in the form of CsCl by spraying the solution
in layers . Lolium perenne seeds, chosen as the test plant, appropriately sown in the pots after 60 days (1st
treatment) and 420 days (3rd treatment) of soil contamination. For all treatments the cultivation period was
110 days. The shoots of Lolium perenne plants were collected at two different intervals - 75 days (1st cut) and
110 days (2nd cut) and prepared for further analyses. To monitor possible changes in soil properties, two
control pots for each treatment were used (pots with no Cs contamination).
In order to examine the relationship between Cs and K ions in the shoots the discrimination factor was used,
according to the equation 1 .
DF = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Cs in soil (mg kg-1) /K in soil (mg kg-1)
2.2 Soil analysis
Four surface soil samples were collected from Kilkis prefecture in Northern Greece, in order to give a range
of physicochemical properties that are important in controlling the availability of Cs in plants. The climate of
this area is typical Mediterranean (mean annual precipitation of 552mm and mean annual temperature of
15oC) and the soil moisture and temperature regimes are xeric and thermic respectively . The soils were
air-dried, passed through a 2 mm sieve and stored before analysis.
Particle size analysis was made using the hydrometer method with a 2 – h reading for clay content . Soil
pH was measured in a 1:1 soil: distilled water (w-v) suspension . Cation exchange capacity was
estimated following the NaOAc method  while exchangeable K+ and Cs+ according to NH4OAc
(pH=7.0) method . The soil samples were treated in duplicates and the means reported.
2.3 Plant analysis
Plant material was dried at 70oC for 48 hours, weighted and ground. 0.5g of the plant sample was dry-ashed
in an oven at 500oC for 4h and the ash was subjected to wet digestion in concentrated nitric acid  Cs and
K concentrations were determined by using a Varian SpectrAA-300 atomic absorption spectrophotometer
Cs in plants (mg kg-1) / K in plants (mg kg-1)
3. RESULTS AND DISCUSSION
Selected physicochemical properties of the studied soils after each treatment are presented in Table 1. The
clay content and exchangeable K concentration, soil properties that influence Cs uptake by plants, were
similar for soils 1 and 4 and 2 and 3 respectively. Exchangeable K content, as an index of soil available K for
plant uptake in all cases was low and clay content ranged between 12 and 45%.
Table 1. Selected properties of the studied soils at the end of each cultivation
Soil 1 Soil 2 Soil 3
Particle size analysis (%)
pH (1:1, s/w)
CEC (meq 100g-1)
Exchangeable K+(meq 100g-1)
before the cultivation
Exchangeable K+(meq 100g-1)
after the cultivation
Exchangeable Cs+(meq 100g-1)
after the cultivation
According to the results, significant differences in Cs plant concentration emerged among the different cuts,
the soil types or the treatments (Figure 1). Regardless to the soil type or treatment, the concentration of Cs in
plants ranged from 95.8 to 287.2 mg kg-1 and from 28.5 to 81.7 mg kg-1 in first and second cut respectively.
Cs concentration was lower in all cases in the second cut, probably due to the shorter plant growth period. Cs
concentration was statistically affected by clay content (1st cut r = 0.679, p<0,05, n=8 / 2nd cut r = 0.796,
p<0.05, n=8) and CEC (1st cut r = 0.767, p<0,05, n=8 / 2nd cut r = 0.874, p<0.1, n=8), suggesting that soil
properties play a predominant role in Cs uptake by plants. In all soil types, exchangeable Cs decreased in the
2nd treatment indicated that as time from contamination increased, the availability of Cs decreased. Although
no specific relationship between Cs concentration in plants and exchangeable Cs in soils was observed.
Figure 1: Cs concentration in the shoots of Lolium perenne plants grown on the four soils, for the 1st
and 2nd cut.
Cesium is weakly hydrated alkaline metal, with chemical similarities to potassium and is predominately
presents in solution as free hydrated cation Cs+, with little on no tendency to form soluble complexes. It can
readily absorbed by plants and can be translocated to the above ground plant parts . Therefore, the
relationship of Cs and K in shoots was also examined, regardless to the variations in Cs concentration in
plants due to the soil type. In both cuts a significant negative correlation between Cs concentration and K
content in the shoots of Lolium perenne plants was observed (1st cut r = -0.874, p<0,01, n=8 / r = -0.900,
p<0.1, n=8, respectively for each cut, Figure 2).
Figure 2: Cs concentrations relationships with K content in the shoots of Lolium perenne plants in the
1st and 2nd cut.
As the Cs concentration decreased, the K content increased in the shoots of Lolium perenne plants. Such a
relationship confirms the occurrence of a direct competition between Cs and K ions during the process of
accumulation through the plant tissues and suggests that the two elements could have a common
accumulation mechanism in plants. It also points to that Cs uptake by plants can be suppressed by the
competition of Cs and K ions in the plant tissues. Similar results are reported by , who showed a similar
relationship between K-Cs in the plant tissues of some tropical and subtropical plants and observed that with
the decrease of Cs levels in plants, K tends to return and to be redistributed in the different plant organs.
Table 2: Discrimination factor (DF) values in the shoots of Lolium perenne plants grown on the four
soils, for the 1st and 2nd cut.
1st Treatment2nd Treatment
The discrimination factor (DF), which is often used to evaluate the plant's efficiency to absorb nutrients from
soil, was additionally estimated, in order to further examine the competitive interactions that occurred
between Cs and K ions (Table 2). Regardless to the treatment or the soil type the DF values were below
unity, suggesting that Cs uptake is less efficiently than its nutrient analogue, K, due to the different
physiological role of the two elements within the plant. It is well known that potassium is an essential
macronutrient for plant growth, that plays an important role in adjusting the osmotic pressure of cells and
maintains the enzyme activity of photosynthesis . Contrary, Cs concentration in plant tissues is less than
1 mg kg-1 and does not have any contribution in plant growth . Thus, it is possible that plants reject Cs+
ions and absorb K+ions, which are necessary for their growth. The results of the present work indicate that K
appears to be one of the main factors influencing plant mobility of Cs and behaves not only as a competitor
to Cs ions, but also as an effective inhibitor of Cs uptake by plant species.
According to the results of the present work, Cs uptake by plants is a consequence of sequence reactions both
in the soil and in the plant, implying that Cs transport from soil to plant is controlled by a complex
mechanism. Therefore the concurrent utilization of soil properties and the K-status in plant tissues is
essential to monitor and to estimate soil to plant Cs mobility. The findings of this study strongly
suggest that it is important to understand the accumulation process of Cs on soil-plant system, in order to
understand the fate of Cs in the soil ecosystem and hereupon in the biotic and non biotic components of the
environment and to facilitate the implementation of successful environmental prevention/remediation
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