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Published online 7 November 2005
Published in J Environ Qual 34:2167-2173 (2005)
DOI: 10.2134/jeq2004.0406
© 2005 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
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Rhizosphere Conference

Rhizospheric Mobilization and Plant Uptake of Radiocesium from Weathered Micas

I. Influence of Potassium Depletion

A. Gommersa, Y. Thirya,* and B. Delvauxb

a Radiation Protection Research Unit, Radioecology Section, SCK•CEN, Foundation of Public Utility, Boeretang 200, 2400 Mol, Belgium
b Unité Sciences du Sol, Université catholique de Louvain, Place Croix du Sud 2/10, 1348 Louvain-la-Neuve, Belgium

* Corresponding author (ythiry{at}sckcen.be)

Received for publication October 28, 2004.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Potassium depletion in the soil solution around plant roots promotes the root uptake of radiocesium. However, it can also induce the transformation of mica through the release of interlayer K. In bulk soil, the formation of frayed edge sites (FES) with a high selectivity for Cs adsorption is usually related with mica weathering. We studied the effect of K level in the nutrient solution on the root-induced weathering of phlogopite as well as on the root uptake of radiocesium by willow (Salix viminalis L. var. Orm). The willows were grown for 7 wk in column lysimeters filled with a quartz–phlogopite mixed substrate continuously irrigated with nutrient solutions differing in K concentration (0–2 mM). From a potassium supply of 0.4 mM downward, we observed a decrease in root uptake of potassium as well as an increase in (i) potassium release from phlogopite, (ii) degree of transformation of phlogopite into vermiculite, and (iii) root uptake of radiocesium. Increasing K depletion had thus two effects: a decrease of the root uptake of potassium and an increase of phlogopite weathering in the rhizosphere, both of which promoted the root uptake of radiocesium.

Abbreviations: FES, frayed edge sites • TF, transfer factor • XRD, X-ray diffraction


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE SOLUBLE POOL of an element in soil is often considered as a predominant parameter of element bioavailability. Plant uptake of radiocesium is thus expected to be controlled by its concentration in the solution around the roots. However, it significantly increases with decreasing K concentration at K levels below 1 mM, as demonstrated in hydroponics (Cline and Hungate, 1960; Gommers et al., 2000; Shaw et al., 1992; Smolders et al., 1996). The K concentration in the soil solution exerts a similar influence on radiocesium uptake by plant roots (Sanchez et al., 1999; Smolders et al., 1997). Yet, the K concentration near the root surface is difficult to determine in situ and does not equal the concentration measured in the bulk solution, which complicates the prediction of radiocesium uptake (Waegeneers et al., 2001). Plant uptake of potassium generates an acute K depletion around the roots where K levels may decrease to as low as 2 µM, and thereby results in a strong gradient of K from the bulk soil to the rhizosphere (Claassen and Jungk, 1982; Hinsinger and Jaillard, 1993). Potassium depletion in the rhizosphere contributes to the transformation of mica, as plant roots are able to induce the removal of interlayer K (Hinsinger and Jaillard, 1993; Mortland et al., 1956; Spyridakis et al., 1967). Through this process, the micaceous 1.0-nm layer silicates are weathered into vermiculitic 1.4-nm layers (Hinsinger and Jaillard, 1993). This transformation may strongly reduce the mobility and bioavailability of radiocesium because trace Cs is fixed specifically on the vermiculitic frayed edge sites (FES) of weathered mica (Cremers et al., 1988; Maes et al., 1998, 1999a; Thiry et al., 2000). Reduction of trace Cs mobility was indeed linked to root activity (Guivarch et al., 1999). Potassium depletion in the rhizosphere can thus involve two opposing effects: (i) enhancement of root uptake of radiocesium and (ii) specific retention of trace Cs on FES generated by mica weathering, hence a reduction of radiocesium mobility. The FES and plant root thus act as mutual competitive sinks for trace Cs in the rhizosphere (Delvaux et al., 2000).

In this research, we measured the root uptake of radiocesium in an experimental rhizosphere involving mica and different K levels in the liquid phase. We used phlogopite as mica and willow as plant material. Root-induced weathering of phlogopite is rapid and leads to large release of interlayer potassium (Hinsinger and Jaillard, 1993). Willow is a high K-demanding plant, exhibits rapid growth, and absorbs increasing amounts of radiocesium with decreasing K bioavailability (Gommers et al., 2000; Thiry et al., 2001).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Phlogopite Mineral
We used a phlogopite, a trioctahedral mica, obtained from Cogebi, division of Compagnie Royale Asturienne des Mines S.A., Brussels, Belgium. The mineral was milled and sieved at 100 to 200 µm. Total element contents were determined by inductive coupled plasma–atomic emission spectrometry (ICP–AES; Jarrell Ash, Franklin, MA), after borate fusion at 1000°C (Voïnovitch, 1988) and dissolution of fusion beads in 2 M HNO3. The Fe(II) content was determined separately by a modified Brinhmann method, and the Fe(III) content was computed as the difference between total Fe and Fe(II) contents.

Experimental Setup and Growth Conditions
Several aliquots of the 100- to 200-µm mineral stock were equilibrated with respective nutrient solutions of different K concentrations until the K levels in the supernatant differed by less than 10% of the initial concentration. The five respective K concentrations were 0, 0.05, 0.1, 0.4, and 2 mM. The treatments will further be referred to as P0, P0.05, P0.1, P0.4, and P2, with P indicating the phlogopite mineral and the number indicating K concentration (mM). In the P0 treatment, the final K concentration was below 20 µM and the composition of the nutrient solution was as follows: 4.55 mM Ca(NO3)2, 1.45 mM MgSO4, 0.2 mM CaHPO4, 25 µM FeEDTA, 10 µM NaCl, 12 µM MnSO4, 43 µM H3BO3, 1.8 µM ZnSO4, 0.3 µM CuSO4, and 0.07 µM (NH4)6MO7O24. With increasing K concentration, Ca concentration in the added solution was decreased to keep the ionic strength of the solution constant for all treatments. The Ca(NO3)2 concentrations were 4.525 mM in P0.05, 4.50 mM in P0.1, 4.35 mM in P0.4, and 3.55 mM in P2. After equilibration, the same amounts of trace 134Cs+ with a specific activity of 113 MBq mg–1 of Cs were added to each solution and were allowed to sorb on phlogopite particles for 7 d (end-over-end shaking). After settling of the minerals, the solutions were decanted and the minerals were dried at 30°C. The radiocesium content in the phlogopite particles and in solution was measured by {gamma}-counting (NaI detector; Minaxi {gamma} 5000 series; Packard, Meriden, CT) and the solid–liquid distribution coefficient Kd (Bq g–1 phlogopite/Bq mL–1 solution) was calculated. The cation exchange capacity (CEC) was determined by AgTU (Chhabra et al., 1975).

For each treatment, the 134Cs-contaminated phlogopite particles (100–200 µm) were mixed with quartz (500–1000 µm) with a ratio of 1 g phlogopite to 99 g quartz. The quartz had been previously washed three times with 12 M HCl (50 mL per kg of quartz) and then abundantly rinsed with deionized water. Fifteen lysimeter columns were filled with the quartz–phlogopite substrate (five treatments, three repetitions). The experimental setup is illustrated in Fig. 1 . The columns (height: 30 cm; diameter: 9 cm) were closed at the bottom with a 20-µm mesh net, allowing the excess solution to be collected below. A porous plate, previously saturated with the nutrient solution, was put on top of it to distribute the added nutrient solution evenly over the surface.



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  		Fig. 1. Schematic representation of the experimental cropping device.

 
One willow cutting was planted in each column. All cuttings were collected from 1-yr-old branches on the same tree. The cropping systems were installed in a greenhouse with a cycle of 16 h of light and 8 h of dark and a minimum light intensity of 425 µmol photons m–2 s–1 being supplied by Philips (Eindhoven, the Netherlands) SON-T 400 daylight lamps (380–779 nm). The plants were grown for 7 wk with a mean temperature of 15°C during the night and 25°C during the day, and a relative humidity varying between 18 and 72%. For each treatment, the columns were supplied with the respective nutrient solution that was added with a peristaltic pump. The flow was modified according to the growth rate of the plants and related transpiration to obtain a percolate volume of >200 mL wk–1.

Percolate and Mineral Sampling and Analysis
During the experiment, the percolates were collected below each column, and the volume of each solution was measured. The different solutions were analyzed for K concentration by atomic absorption spectrometry (AAS) and radiocesium content by {gamma}-counting.

At harvest, the plant shoots were cut just above the quartz–phlogopite substrate and stored apart. The columns were then opened and the whole substrate was taken out from the column. The root system was carefully removed along with the adhering quartz–phlogopite mixture, and was separated from the non-adhering substrate. The roots were gently shaken to remove part of the quartz–phlogopite mixture that did not stick to the roots (Courchesne and Gobran, 1997): this part together with the non-adhering substrate was considered as bulk soil. Rinsing the roots with ethanol 99.8% further isolated the substrate firmly adhering to the root: this part was considered as rhizosphere soil.

For each treatment and repetition, a sample was taken from the bulk and the rhizosphere volume. Phlogopite particles were separated from quartz by wet sieving with ethanol through a 0.5-mm sieve, and were then dried at 30°C. Total 134Cs content of the particles from both rhizosphere and bulk soil as well as from the initial stock (i.e., just after equilibration) was determined by {gamma}-counting. Total K content was measured by ICP–AES, after fusion and wet digestion of the sample as described above. Exchangeable K+ and 134Cs+ contents were measured by AAS and {gamma}-counting in 0.006 M and 0.5 M CaCl2 extracts (0.1 g phlogopite to 10 mL solution), respectively. X-ray diffraction (Cu-K{alpha}, Bruker D8; Bruker, Rheinstetten, Germany) was performed on samples previously air-dried on glass plates.

Plant Sampling and Analysis
The shoots of each plant were separated in leaves and stems. After extraction of the root ball from the substrate and washing as described above, the roots were separated from the cuttings. Before analysis, the roots were washed free of phlogopite particles with ethanol. All plant materials were dried at 105°C and weighed to determine the net biomass produced during the experiment. For each plant compartment, the 134Cs content was determined by {gamma}-counting. The K content was determined by AAS after calcination at 550°C, and ash dissolution with 1.5 mL of 12 M HCl.

The phlogopite-to-willow 134Cs transfer was first computed as a transfer factor (TF) for each plant part (leaf, stem, root, cutting):

where [134Cs]plant part was the radiocesium content in plant compartment (Bq g–1 dry wt.) and [134Cs]initial phlogopite particles the radiocesium content of phlogopite particles of the initial substrate (Bq g–1 dry wt.). A TF for the whole plant (TFtotal plant) was then calculated by using a weighed radiocesium plant content (i.e., by considering the respective biomass of the different plant compartments).

In our experimental conditions, phlogopite was the sole source of radiocesium for plant uptake in all treatments, but the sole source of potassium only in P0. In contrast, part of potassium absorbed by the plants could be derived directly from aqueous nutrient supply in the P0.05, P0.1, P0.4, and P2 treatments. The amount of plant potassium derived from the nutrient solution was computed as the difference between the amount of K supplied to each column and that measured in the percolates. The additional amount of K was assumed to derive from phlogopite.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Mineral Characteristics
The elemental composition of the mineral is given per half unit cell in Table 1. Octahedral occupancy (2.89 cations per half unit cell) as well as large K, Mg, and Fe(II) contents all confirmed its identification as a phlogopite. This conclusion was also supported by the occurrence of both the 060 X-ray diffraction (XRD) reflection at 0.153 nm (not shown) and the typical 001 reflection at 1.0 nm (bulk sample in Fig. 6). Some of the characteristics of the phlogopite sample after equilibration with the respective nutrient solutions (P0, P0.05, P0.1, P0.4, P2) and 134Cs contamination are illustrated in Table 2. The values of the AgTU-CEC progressively increased from 30.7 (P2) to 41.4 (P0) cmolc kg–1 with decreasing K concentration in the liquid phase (i.e., from P2 to P0 scenario). This increase could be related to the access of interlayer space of mica to exchangeable cations. However, the exchangeable K content was fairly constant, whereas the total K content did not vary and mica transformation was not detectable by XRD (not shown). Yet, exchangeable 134Cs content progressively increased from 46.3 to 58.6 Bq g–1 with decreasing K concentration (i.e., from P2 to P0). This increase was parallel to a 47-fold augmentation of KdCs from 127 (P2) to 5945 mL g–1 (P0).


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  		Table 1. Elemental composition per half unit cell [/O10(OH)2] of the phlogopite mineral.

 


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  		Fig. 6. X-ray diffraction (XRD) patterns of the rhizosphere phlogopite at different levels of external K supply (from P0 to P2). The XRD pattern of bulk phlogopite as observed in the different treatments is presented for comparison. The intensity ratio of the 1.4- to 1.0-nm reflection (I1.4/I1.0) for rhizosphere phlogopite are 0.00 in P2, 0.15 in P0.4, 0.26 in P0.1, 0.33 in P0.05, and 0.30 in P0.

 

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  		Table 2. Characteristics of the phlogopite particles (100–200 µm) after equilibration with the respective nutrient solution and contamination with radiocesium (average value ± standard deviation, n = 3).

 
Percolate Composition
The evolution of K concentrations in the percolates is shown in Fig. 2 . In each treatment, K concentration was relatively constant until Day 20. Afterward, the K concentrations sharply decreased in P0.4, P0.1, and P0.05, but not in P2, where the K concentration was relatively stable at 2 mM. In P0, the K concentration slightly increased from 0.015 to 0.031 mM due to potassium leaching derived from phlogopite, which constituted the sole K source in the system. A comparison between K and 134Cs concentrations of the percolates at the end of the experiment is presented in Table 3. Small differences were observed between the P0, P0.05, and P0.1 scenarios, where the K concentration was around 0.025 mM. Both K and 134Cs concentrations of the percolates were much larger in P2 than in the four K-depleted treatments (P0.4, P0.1, P0.05, and P0).



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  		Fig. 2. Variation of potassium concentrations in the percolates of the different treatments (left: P0, P0.05, P0.1; right: P0.4, P2) during the experimental period.

 

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  		Table 3. Potassium and radiocesium concentrations of the percolates below lysimeter columns at the end of the experiment.

 
Potassium and Cesium-134 Acquisition by Plants
The net biomass produced during the experimental period differed up to 1.8-fold between the K treatments (Fig. 3) . A K concentration above 0.1 mM in nutrient solution (P2 and P0.4) resulted in the largest biomass production. The influence of the external K supply was also reflected in 134Cs plant uptake and plant K content as illustrated in Fig. 4 . The 134Cs TFs for the total plant (stem + leave + roots + cutting) was reduced by eightfold with increasing K supply from P0 to P2, while plant K content increased, the K content of P2 plants being twice as large as that of the P0 plants. In the P0.05, P0.1, P0.4, and P2 treatments, the contribution of nutrient solution as a source of plant K was computed by comparing the total amount of K incorporated into the plant with that removed from the solution (i.e., not recovered in the percolates) (Fig. 5) . With increasing K supply (from P0 to P2), the total plant K increased 3.3-fold. The estimated amount of K removed from solution was similar to the K amount measured in P2 plants, illustrating that K supply was sufficient to cover plant K requirements. The contribution of external supply was reduced in K-depleted treatments: it accounted for 61% of K plant uptake in P0.4, 21% in P0.1, 12% in P0.05, and 0% in P0. The remaining part of plant K was thus mobilized from phlogopite particles, and that fraction increased with decreasing K external supply.



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  		Fig. 3. Net biomass (dry weight) produced by willow under varying potassium supply.

 


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  		Fig. 4. Average total potassium content of plants (left) and radiocesium transfer factor (TF) (right) for each treatment.

 


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  		Fig. 5. Comparison between the amount of potassium removed from the nutrient solution percolating in the lysimeter column (K-solution) and the amount of potassium exported by willow plant in the different treatments (K-plant).

 
Changes in Chemical Composition of Phlogopite
Changes in total and exchangeable contents of 134Cs and K in phlogopite from bulk and rhizosphere samples are presented in Table 4. Total 134Cs and K contents did not differ between initial and bulk phlogopite in P2. In other treatments, the total 134Cs content of initial phlogopite exceeded that of the bulk fraction and the differences increased with increasing K depletion (from P0.4 to P0). The reduction in 134Cs concentration was more than 50% in P0. Similar observations were made for total K concentration but the differences were much lower and accounted for less than 11% for P0. We assumed that a small part of the phlogopite particles, probably the finest fraction, was lost during the separation of quartz and phlogopite particles by wet sieving at 100 µm.


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  		Table 4. Total and exchangeable radiocesium and potassium contents of the various fractions of the phlogopite particles (initial, bulk, and rhizosphere) for the different treatments (average value ± standard deviation, n = 3).

 
As for the rhizosphere fractions, the total K content was lower than that of the bulk fraction in all treatments, except in P2. The differences tended to increase with lower K supply. The decrease was not significant in P0.05 due to very large differences between replicates. Similarly, total 134Cs content decreased in K-depleted treatments (from P0.4 to P0) from bulk to rhizosphere minerals, but differences between bulk and rhizosphere minerals were not significant due to large variability among the replicates.

Before planting, the initial content of exchangeable K decreased from 0.20 to 0.16 mg g–1 from P2 to P0, reflecting the decrease in K concentration of the nutrient solutions. After harvesting, the content of exchangeable K was kept above 0.2 mg g–1 in P2, but significantly decreased in the K-depleted treatments, particularly in the rhizosphere of plants grown in the P0 and P0.5 treatments. In the P2 treatment soil, the contents of exchangeable 134Cs did not differ between initial and treated samples, either in the rhizosphere or in the bulk volume. They significantly differed, however, in K-depleted scenarios, as these contents were smaller in treated samples than in initial ones. These results show a larger mobilization of K and 134Cs in the K-depleted treatments than in P2, especially from the rhizosphere.

Changes in Phlogopite Characteristics
The X-ray diffraction patterns of bulk and rhizosphere phlogopite particles are presented in Fig. 6 . Irrespective of the potassium scenario, the bulk minerals exhibited the typical 001 reflection of mica at 1.0 nm. The rhizosphere minerals behaved differently, except in the P2 treatment where both bulk and rhizosphere minerals exhibited the typical mica XRD features. From P0.4 to P0, a distinct 001 reflection at 1.4 nm typical for vermiculite was observed. Moreover, the intensity of this reflection progressively increased from P0.4 to P0. As measured on XRD patterns, the intensity ratio of the 1.4- to 1.0-nm reflection (I1.4/I1.0) increased from 0.00 in P2 to 0.15 in P0.4, 0.26 in P0.1, 0.33 in P0.05, and 0.30 in P0, reflecting a larger transformation of phlogopite into vermiculite in the rhizosphere.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
Transformation of Phlogopite
The XRD features did not show any transformation of phlogopite into vermiculite before planting, just after equilibration with the respective nutrient solutions and 134Cs sorption. Yet, there was a parallel increase of both the exchangeable 134Cs content and KdCs with decreasing K level. This could be related either to an increase in Ca saturation leading to increased selective sorption of Cs against K on FES (Coleman et al., 1963) or to very small but genuine generation of FES. Formation of FES could indeed arise from limited transformation of mica in vermiculite in K-depleted conditions (Maes et al., 1999b). This transformation was anyway very limited, and not detectable by X-ray diffraction. It is worth noting that the increase of KCsd with decreasing K level is a signature of specific sorption of trace Cs onto FES (Comans et al., 1991). This is of course expected, as a seemingly negligible amount of FES can still be large enough to develop specific trace Cs sorption effects, as shown in soils with undetectable weathered mica (Wauters et al., 1996a; Wauters et al., 1996b).

After the experimental treatment phase, the XRD features of initial and bulk phlogopite particles did not differ, suggesting no mica transformation in the bulk substrate or at least none that was detectable by XRD. In the K-depleted treatments (P0–P0.4), the parallel increase of the XRD intensity ratio (I1.4/I1.0) and decrease of total K content from bulk to rhizosphere showed that phlogopite was readily but only partly transformed into vermiculite in the rhizosphere of the willow plants. The removal of potassium from the expanded part of the transformed mica (Sawhney and Voigt, 1969) may explain the decrease in K content in rhizosphere phlogopite. The partial transformation of phlogopite was more advanced as K concentration decreased in the liquid phase (i.e., from P2 to P0). These observations confirm the rapid weathering of phlogopite in the rhizosphere, as influenced by K depletion (Hinsinger and Jaillard, 1993). The concentration of potassium in the percolates in most K-depleted conditions (P0–P0.1) stabilized at about 0.03 mM (Table 3). This concentration was considered as the equilibrium concentration, which was kept constant by the release of interlayer potassium. The release of potassium and the subsequent mica weathering occurred, however, already in P0.4 where the K concentration in the percolates was 0.06 mM. This threshold level was slightly smaller than the 0.08 mM threshold value proposed by Hinsinger and Jaillard (1993) for root-induced weathering of phlogopite. These authors used, however, phlogopite particles calibrated at 2 to 105 µm, while we used in this study 100- to 200-µm particles. This difference in size might explain the smaller threshold value proposed here. The release of interlayer K is indeed easier for smaller than for larger particles if the concentration gradient is maintained during extraction as it occurs during root uptake (Cox and Joern, 1997; Fanning and Keramidas, 1977; Von Reichenbach and Rich, 1969).

Plant Acquisition of Potassium and Radiocesium
Since willow species are high K-demanding plants during the establishment phase (Ericsson, 1984; Perttu, 1998), plant growth was limited by low K levels. The increase in plant potassium content and biomass with increasing external potassium supply confirms that K concentration in the liquid phase is an important factor determining potassium uptake by plant roots (During and Duganzich, 1979; Schroeder, 1974).

Unlike the potassium uptake, the absorption of radiocesium by the willow roots significantly decreases with increasing external K supply. In contrast to biomass production and potassium concentration, the 134Cs TF thus increased with decreasing K supply, with maximum values at a K level below 0.4 mM (Fig. 4). Several hydroponic studies have shown that with a 10-fold decrease in potassium concentration from 0.250 to 0.025 mM, the uptake of radiocesium increased 12- to 113-fold (Smolders et al., 1996; Waegeneers et al., 2001). Decreasing K supply also increased the radiocesium uptake by willows in hydroponics. Indeed, a twofold decrease of the K concentration from 0.400 to 0.08 mM resulted in a fourfold increase of the radiocesium concentration in the shoots whereas a decrease from 2 to 0.4 mM did not influence the uptake of trace Cs by willows (Gommers et al., 2000). Our results show that decreasing K supply below 0.4 mM also increased radiocesium uptake by willows in a substrate containing weathered mica, despite the decrease in plant biomass.

Potassium Depletion, Cesium-134 Uptake, and Phlogopite Weathering
Our data provide strong evidence that, apart from the effect of K depletion in the solution on the root uptake of radiocesium, other rhizospheric processes are important in the acquisition of 134Cs by plants.

The rhizosphere effects linked to potassium level in the liquid phase are threefold:


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
We studied the substrate–plant transfer of trace Cs from a K-depleted rhizosphere environment containing phlogopite, a trioctahedral mica. Potassium depletion resulted in a decrease of plant biomass and root uptake of potassium, but in an increase of 134Cs uptake and phlogopite weathering. The mobility of radiocesium was thus not reduced by the formation of vermiculitic frayed edge sites (FES), which would specifically sorb trace Cs ions.

We conclude that, in a rhizosphere containing mica, root uptake of trace Cs in K-depleted conditions is governed by both the root uptake of potassium and mica weathering. This latter process is indeed a prerequisite to the release of both interlayer K and FES-bound Cs. The more acute the K depletion, the larger the release of interlayer K and FES-bound Cs, and the larger the root uptake of trace Cs. The respective importance of root uptake of K and Cs released from FES through mica weathering in the rhizosphere requires further investigation.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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Y. Thiry, A. Gommers, A. Iserentant, and B. Delvaux
Rhizospheric Mobilization and Plant Uptake of Radiocesium from Weathered Micas: II. Influence of Mineral Alterability
J. Environ. Qual., November 7, 2005; 34(6): 2174 - 2180.
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