沙漠研究 22-1, 299 -302 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－Phytodesalination: a Solution for Salt-affected Soils
in Arid and Semi-arid Regions
Walid ZORRIG1)#, Mokded RABHI1)#, Siwar FERCHICHI1), Abderrazak SMAOUI1) and Chedly ABDELLY*1)
Abstract: The present work is a survey of several phytodesalination investigations carried out in our laboratory showing the abilityof some obligate halophytes to desalinize their rhizosphere through field and greenhouse experiments. This evaluation was based on(i) the decrease in soil salinity, sodicity, and sodium concentration, (ii) phytodesalination (PHD) capacity of the halophyte, and (iii) theability of a glycophyte to grow on the desalinized soil. In field experiments, we found that tufts of perennial halophytes such as
Tecticornia indica (Willd.) subsp. indica and Suaeda fruticosa (Forssk.) offer to numerous annual glycophytes a microhabitat favorable
for their development. This was probably due to two major factors: sodium accumulation within the halophyte shoots and thefacilitation of its leaching in the soil. We estimated PHD capacity in a Tunisian sabkha at about 0.65 t Na+. ha-1 in summer and 0.75
t Na+. ha-1 in winter. In greenhouse experiments, tested halophytes (T. indica, S. fruticosa, and Sesuvium portulacastrum) showed
noticeable PHD capacity under non-leaching conditions (about 1 t Na+ ha-1 in the case of S. portulacastrum). On soil taken frominside halophyte tufts, glycophyitic Medicago species exhibited higher biomass production than on soil taken from outside tufts. Inaddition, the cultivation of Hordeum vulgare L. (test culture) on saline soil previously desalinized by S. portulacastrum showed that thedecrease in soil salinity and sodicity was beneficial to coleoptile emergence as well as to biomass production, tissue hydration, sodium
accumulation, and potassium acquisition.
Key Words: Arid and semi-arid regions, Halophytes, Non-leaching conditions, Phytodesalination capacity

1. Introduction
It was postulated that salt-affected soils cover about 6%(more than 800 million ha) of the world lands, which is mainly
due to natural causes (salt accumulation over long periods oftime in arid and semi-arid regions) or to human-induced causesthat affected in 2008 about 2% (32 million ha) of the drylandfarmed areas and 20% (45 million ha) of the irrigated lands inthe world (Munns and Tester, 2008). To overcome thisproblem, several authors (Zhao et al., 2001, 2005; Graifenberg
et al., 2003; Tester and Davenport, 2003; Ravindran et al.,2007; Rabhi et al., 2009, Rabhi et al., 2010a, Rabhi et al.,2010b) have been encouraging this biological approachproving the efficiency of Na+-hyperaccumulating plants todesalinize the soil on which they are cultivated, especially inarid and semi-arid regions, where low precipitations andinappropriate irrigation systems are unable to leach salts fromthe rhizosphere. Soil phytodesalination is based on thecapacity of some halophytes to accumulate enormous sodium
quantities in their shoots (Rabhi et al., 2009, Rabhi et al.,2010a, Rabhi et al., 2010b). The present work is a survey ofseveral phytodesalination investigations carried out in ourlaboratory showing the ability of some halophytes to desalinize

their rhizosphere through field and greenhouse experiments.
This evaluation was based on (i) the decrease in soil salinity,
sodicity, and sodium concentration, (ii) phytodesalination(PHD) capacity of the halophyte (sodium quantity
accumulated within its shoots per hectare), and (iii) the abilityof a glycophyte to grow on the desalinized soil.

2. Materials and Methods
2.1. Field experiment
In this experiment, four different quadrats of 100 m2(10×10 m) were chosen for soil and plant sampling in different
localities in the salt-affected ecosystem, Soliman sabkha (N-ETunisia). Whole tufts of the halophytes Tecticornia indica(Willd.) subsp. and Suaeda fruticosa (Forssk.) were collectedfor shoot dry weight and sodium concentration determinationin HNO3 (0.5%) extracts. Soil samples of the upper 20 cm
were collected from inside and outside halophyte tufts andwere analyzed for ECe and soluble sodium concentration insaturation paste extracts. In both soil and plant extracts, Naconcentration was measured with a Corning spectrophotometer.
Halophyte productivity (Shoot dry weight per hectare) andtheir phytodesalination capacity (PHD capacity = Productivity* Shoot Na concentration) were estimated by a multiplication* Corresponding Author: chedly.abdelly@cbbc.rnrt.tn; chedly.abdelly@gmail.com
P. O. Box 901, 2050 Hammam-Lif, Tunisia1) Laboratory of Extremophile Plants (LPE), Biotechnology Centre of Borj-Cedria,, University of Tunis El Manar# The two first authors equally contributed to the elaboration of this work.

of mean values of the four quadrats by 100.
2.2. Greenhouse experiment under non-leaching conditions
Seedlings of Sesuvium portulacastrum L., T. indica and S.
fruticosa with the same weight were cultivated in pots filledeach with 8 kg saline sodic soil taken from the borders ofSoliman sabkha. For each species, five plants were grown
per pot and irrigated with tap water at almost 50% of the soil
field capacity. Pots with no plantation were considered ascontrol. After 170 days, plants were harvested and theirshoots were weighed and analyzed. Soil samples were also
taken and analyzed. Halophyte productivity was estimatedthrough their density (5 plants per pot), their shoot dry weight,and pot surface.
2.3. Test-culture experiment
The substrate used in this experiment was a loamy sand
(SAR = 5.7 (mmol l-1)1/2 and ECe = 2.4 dS m-1). For plantmaterial, we used S. portulacastrum as phytodesalinating
halophyte and Hordeum vulgare L. (var. Manel) as glycophyte
for the test-culture. The phytodesalination culture wasperformed under non-leaching conditions and lasted 189 days.
Three treatments were used: Control (irrigated with tap waterfrom the beginning to the end of the experiment), Salinized(Watered with NaCl solution up to a soil sodium percentage of
0.25% then irrigated with tap water until the end of theexperiment), and Phytodesalinized (salinized soil on which S.
portulacastrum plants were cultivated and irrigated with tap
water until the end of the experiment). The test-culture wasrealized by sowing H. vulgare seeds in pots of the threetreatments after harvesting the halophyte and mixing the soil ofeach pot separately. Then, pots were irrigated with tap waterfor 30 days. As for the two previous experiments, at the endof each culture, soil and plant samples were taken andanalyzed.

3. Results and Discussion
3.1. Field experiment
ECe values were 2.8-4.9 times higher in outside-tuft than ininside-tuft soil in both July and February samples (Table 1).
In inside-tuft soil, the decrease between summer and winterwas 42-57%. The same tendency was found in soluble
sodium concentrations. This suggests Na+ removal by thehalophytes either through its accumulation in shoots and/orthrough facilitating its leaching.
T. indica productivity (7.42 t DW ha-1) was shown to be
several times that of S. fruticosa (2.19 t DW ha-1; Table 1).
This was due to (i) the higher capacity of the former to produceshoot phytomass, and (ii) to its noticeable predominance within

Table 1. Soil ECe and soluble Na concentration and halophyte
productivity and phytodesalination (PHD) capacity
measured in summer 2007 and in winter 2008. Values aremeans of 6 replicates. Means followed by the same letter are
not significantly different according to Duncan’s test at 5%.
Soil and plant samples were taken from outside halophyte tufts(OT) and inside T. indica (TI) and S. fruticosa (SF) ones.
Summer

WinterOT

TISFOT

TISF

75.6d

27.2b

25.4b

57.4c

11.8a

14.8a

0.63c

0.44b

0.38b

0.64c

0.19a

0.18a

Productivity (t DW. ha )

0.00a

7.42c

2.19b

0.00a

7.42c

2.19b

PHD capacity (t Na+. ha-1)

0a0.64c

0.04b

0a

0.75c

0.22b

ECe (dS. m-1)
Soluble Na (%)-1

Table 2. ECe and soluble Na concentration of a naturally
salt-affected soiland plant
productivityandphytodesalination (PHD) capacity after a 170-day culture ofS. portulacastrum, T. indica and S. fruticosa.
Forproductivity and PHD capacity, values are means of 6 replicates.
Values followed by the same letter are not significantly different
according to Duncan’s test at 5%.
S. portulacastrum

T. indica

S. fruticosa

ECe (% of the control)

293545Na+ (% of the control)

46

52

61

6.64b

2.32a

2.04a

0.99b

0.26a

0.36a-1

Productivity (t DW ha )+-1

PHD capacity (t Na ha )the ecosystem. In winter, both halophytes experienced highshoot sodium concentration, whereas in summer, a marked
decrease was found in S. fruticosa.
Accordingly, we observed higher phytodesalination (PHD)
capacity (sodium quantity accumulated in shoots per hectare)in T. indica than in S. fruticosa (Table 1). The whole quantityof sodium removed by the two halophytes was 0.69 and 0.97 t
ha–1 in July 2007 and February 2008, respectively.
This experiment revealed two major findings: 1)
Phytodesalination depends on plant species, soil properties(salinity, sodicity, and porosity), and climatic conditions(mainly rainfall) (Rabhi et al., 2010a). 2) The removed
sodium quantity is not exclusively accumulated in halophyteshoots since a part can be due to leaching process (Qadir andOster, 2004; Rabhi et al., 2009; Rabhi et al., 2010a). For thisreason, we carried out a greenhouse investigation underzero-leaching conditions.
3.2. Greenhouse experiment under non-leaching conditions
We found a high capacity in the three halophytes to extract
soil sodium and to decrease soil salinity. ECe was reduced to29, 35, and 45% of the control by S. portulacastrum, T. indica
and S. fruticosa, respectively (Table 2). Our results revealed
also similar variations in the soil soluble sodium concentrations,indicating the high ability of the three species to remove thisTable 3. ECe, soluble Na concentration, and SAR of the upper 10 cm
of an experimentally salt-affected soil after a 189-day cultureof S. portulacastrum. Values are expressed as % of thecontrol.

ECe

Salinized

Phytodesalinized299232

Table 4. Final percentage of coleoptile emergence, biomass
production, tissue hydration, and sodium and potassium
concentrations in H. vulgare plants grown on salinized andphytodesalinized soils. Values are expressed as % of thecontrol.
Salinized

Phytodesalinized

4474

SAR

862

580

Coleoptile emergence

Soluble Na+474

320

Plant biomass

841

Shoot water content

64

81

Shoot sodium concentration

138

98

Shoot potassium concentration

46

62

Root water content

4467

Root sodium concentration

113

101

Root potassium concentration

43

42

cation from the soil.
Our estimations showed considerable productivity in thethree halophytes, mainly S. portulacastrum that was able toproduce 6.6 t DW ha-1. High PHD capacities were also
observed in the three halophytes, the highest being found in S.
portulacastrum (0.99 t Na ha-1, which is the equivalent of 2.5 t
NaCl ha-1; Table 2).
From this work, we concluded that S. portulacastrum was
the most promising halophyte. Ravindran et al. (2007)
estimated its PHD capacity after a 4-month culture to 0.47 t
NaCl ha-1. These findings are interesting and encouraging,
however, the decrease in soil salinity and sodicity does notnecessarily ensure an amelioration of a glycophyte if cultivatedon. Therefore, we performed a test-culture to check whether
the glycophyte H. vulgare can be grown on a phytodesalinizedsoil.
3.3. Test-culture experiment
The soil salinization led to an increase of ECe in the upper
10 cm of the soil (299% of the control; Table 3). SAR andsoluble sodium concentration reflected the results of ECe; they
were increased in the salinized soil to 862 and 474% of thecontrol, respectively. These high values of ECe, SAR, andsoluble sodium concentration were reduced in thephytodesalinized treatment to 232, 580, and 320% of thecontrol, respectively. This confirms the idea of a high PHD
capacity in the shoot succulent halophyte, S. portulacastrum.
Our findings were supported by a noticeable ameliorationof H. vulgare coleoptile emergence, growth, tissue hydration,
sodium accumulation, and potassium status as grown on
phytodesalinized soil (Table 4). In literature, little is known
about test-cultures. Abdelly et al. (1995) took soil frominside and outside perennial halophyte tufts and grewMedicago species (glycophytes) on. They observed that on
soil taken from inside halophyte tufts, glycophyitic Medicago
species exhibited higher biomass production than on soil takenfrom outside tufts.
Ecologically speaking, perennial
halophytes offer to numerous annual glycophytes a
microhabitat suitable for their development (Abdelly et al.,1995).
This experiment showed also that salinity and sodicity inthe layer 10-20 cm of the phytodesalinized soil were increased
due to the halophyte root effects (non-shown data). Indeed,vegetative bioremediation of the upper horizon was due not
only to phytodesalination but also to sodium leaching to thelower horizon. According to Qadir and Oster (2004), thedecrease in soil sodium concentration, and consequently soil
salinity/sodicity, occurs in two steps: 1) its release from cationexchange sites through an increase of CO2 partial pressure
within the root zone (and root proton release in the case of
N2-fixing plants) then 2) its removal from the upper horizons
through leaching and/or phytodesalination.

4. Recommendation
Phytodesalination is an emerging technique that can beused to cope with salinity/sodicity problems in arid andsemi-arid regions. However, its application requires anoptimization, including the choice of the convenient halophyte
and the season of its culture. In addition, extremely
sodic/saline soils cannot be phytodesalinized. Plants used forphytodesalination purposes can have several post-harvest uses
(fodder, biofuel production, oil extraction, essential oilextraction, medicinal uses…) and can thus have twosimultaneous beneficial utilizations.

Acknowledgment
All works described in this survey were supported by theTunisian Ministry of Higher Education and Scientific Research(LR10CBBC02).
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