Salinty n Hypoxia Interaction in Eucalptus

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Different Eucalyptus Species Show Different Mechanisms of Tolerance toSalinity and Salinity × HypoxiaMuhammad Nasim a; Riaz H. Qureshi b; Tariq Aziz a; M. Saqib b; Shafqat Nawaz a; J. Akhtar b; M. A. Haq b;Shahbaz Talib Sahi a

a Sub-Campus Depalpur, University of Agriculture, Faisalabad, Depalpur, Pakistan b Saline AgricultureResearch Centre, University of Agriculture, Faisalabad, Depalpur, Pakistan

Online Publication Date: 01 September 2009

To cite this Article Nasim, Muhammad, Qureshi, Riaz H., Aziz, Tariq, Saqib, M., Nawaz, Shafqat, Akhtar, J., Haq, M. A. and Sahi,Shahbaz Talib(2009)'Different Eucalyptus Species Show Different Mechanisms of Tolerance to Salinity and Salinity ×Hypoxia',Journal of Plant Nutrition,32:9,1427 — 1439

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Journal of Plant Nutrition, 32: 1427–1439, 2009

Copyright © Taylor & Francis Group, LLC

ISSN: 0190-4167 print / 1532-4087 online

DOI: 10.1080/01904160903092648

Different Eucalyptus Species Show Different

Mechanisms of Tolerance to Salinity

and Salinity × Hypoxia

Muhammad Nasim,1 Riaz H. Qureshi,2 Tariq Aziz,1 M. Saqib,2

Shafqat Nawaz,1 J. Akhtar,2 M. A. Haq,2 and Shahbaz Talib Sahi1

1Sub-Campus Depalpur, University of Agriculture, Faisalabad,Depalpur, Pakistan

2Saline Agriculture Research Centre, University of Agriculture, Faisalabad,

Depalpur, Pakistan

ABSTRACT

We studied the effect of sodium chloride (NaCl) salinity and oxygen deficiency stresson growth and leaf ionic composition of three Eucalyptus species [ E. tereticornis, E.

camaldulensis (Silverton), and E. camaldulensis (Local)]. Species were grown with

control (no NaCl) and salinity (150 mol m−3 NaCl) under hypoxic and non-hypoxic

conditions in nutrient solution with five replications following CRD. Species differed

significantly in their response to salinity and hypoxia. Absolute shoot dry matter was

significantly better in E. camaldulensis (Silverton) in salinity and in E. camaldulensis

(Local) in saline hypoxic treatment. E. tereticornis was the most sensitive species to

salinity and salinity× hypoxia in the root environment. Sodium (Na+) and chloride (Cl−)

concentrations were significantly lower in E. camaldulensis (Local) in non-hypoxic

saline treatment compared to the other two species. E. camaldulensis (Silverton) seemsto have better tissue compartmentalization, whereas E. camaldulensis (local) seems to

have better exclusion of Na+ at the root level.

Keywords: salinity, hypoxia, Eucalyptus, leaf expansion, growth, ionic composition

INTRODUCTION

Desertification of arable lands is a serious threat to agriculture around the globe.

Salinization is an important factor contributing to the degradation of the arable

Received 29 October 2007; accepted 17 July 2008.

Address correspondence to Dr. Muhammad Nasim, University of Agriculture,

Faisalabad, Sub-Campus Depalpur, Depalpur, Okara, Pakistan. E-mail: mnasimshahid@

yahoo.com

1427

D o w nl o ad ed B y : [ N a si m , M uh a m m

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1428 M. Nasim et al.

lands particularly in arid and semi-arid regions (Ashraf, 1994). Approximately

6.3 million hectares of agricultural land in Pakistan is affected by varying

degrees of salinity/sodicity (Ghafoor et al., 2004) that adversely affects plantgrowth and yield in a number of species (Eom et al., 2007). Soil salinity affects

plant growth mainly through osmotic effects and specific ion toxicities (Grattan

and Grieve, 1999; Munns, 2002; 2005) resulting from accumulation of sodium

and chloride in the plant tissues (Saqib et al., 2004a; 2005a; Rezaei et al.,

2006). Sodium (Na) concentration in tissues and potassium (K+): Na+ ratios

are extensively used in screening mass germplasms as selection parameters

(Saqib et al., 2004a; Tahir et al., 2006).

Salt affected soils (mainly those with high sodium) are generally dispersed

soils having low soil permeability, porosity, and hydraulic conductivity (Qadiret al., 2005). Low water infiltration and soil dispersion poses a serious drainage

problem and may lead to waterlogging. Plant roots affected by waterlogging are

deprived of sufficient oxygen resulting in a change in the mode of respiration

from aerobic to an-aerobic and low energy production (Marschner, 1995). Low

energy production in roots disturbs the nutrient and water uptake (Jackson,

1979; Morard and Silvestre, 1996). Waterlogging also reduces nutrient uptake

that results in nutrient deficiency in shoot leading to reduced shoot growth

(Trought and Drew, 1980). Higher abscisic acid production and movement

to younger leaves under oxygen (O2) deficiency causes stomatal closure inplants (Zhang and Zhang, 1994) affecting photosynthesis and ultimately yield.

Waterlogging also affects sodium exclusion from plant roots, which is a major

salinity tolerance mechanism in various glycophytes (Barrett-Lennard, 1986;

Saqib et al. 2005a). A combined effect of salinity and waterlogging on plant

growth is more damaging than caused by salinity and waterlogging alone

(Qureshi and Barrett-Lennard, 1998; Saqib et al., 2004a).

Although several relatively salt tolerant cultivars of different agronomic

crops are available to grow on moderately salt affected soils yet these culti-

vars fail to produce economical yields on highly degraded salt affected soils.Reclamation of such soils through physical and chemical approaches is also

not feasible. Revegetation of these lands with salt tolerant tree species is a vi-

able approach mainly because of low input and increased demand of wood for

fuel and furniture. Selection of suitable tree species is a pre-requisite for such

biological remediation approach. However, very little work has been reported

on this aspect particularly on tree species. The present paper reports the effect

of salinity and hypoxia interaction on growth and leaf ionic composition of

three Eucalyptus species.

MATERIALS AND METHODS

Site and Environmental Conditions

The experiment was conducted in a rain-protected wire house at the Insti-

tute of Soil & Environmental Sciences, University of Agriculture, Faisalabad,


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Salinity × Hypoxia Interaction in Eucalyptus 1429

Pakistan. Faisalabad is situated at 73.4◦ longitude and 31.5◦ latitude. The aver-

age day and night temperatures during the study were 32 and 20◦C, respectively,

while the average maximum relative humidity was 70%, and there was 7 h av-erage daily sunshine during the growth period.

Plant Material and Experimental Details

Seeds of three Eucalyptus species [E. tereticornis, E. camaldulensis (Silver-

ton), and E. camaldulensis (Local)] were collected from Australian Revegeta-

tion Corporation Limited, Western Australia and Saline Agriculture Research

Centre, University of Agriculture, Faisalabad, Pakistan. Fifty seeds of each

species were sown in polyethylene lined iron trays containing silica gravel and

synthetic vermiculite (mixed in 1:1 ratio). The canal water was used to moisten

the seeds for proper germination. Electrical conductivity of canal water was

0.29 d Sm−1. One week after germination, half strength Hoagland’s nutrient

solution (Hoagland and Arnon, 1950) was used for the seedling establishment.

Seedlings were grown for three months in these trays. Uniform sized seedlings

were then transplanted in foam plugged holes in polystyrene sheets floating

on continuously aerated half strength Hoagland’s nutrient solution contained

in polyethylene lined iron tubs of 200 L capacity (100 × 100 × 30 cm3).

The experiment was replicated five times following completely randomized

design (CRD). Solution pH was monitored and maintained daily at 6 ± 0.5.

There were four treatments viz i) non-saline non-hypoxic (control), ii) saline

non-hypoxic, iii) non-saline hypoxic, and iv) saline-hypoxic. Salinity level for

saline treatment was 150 mol m−3 sodium chloride (NaCl). The salinity was

developed in three equal splits in a week (each of 50 mol m−3 NaCl after 2

d). The hypoxia was imposed by surface sealing of the nutrient solution. Three

days after surface sealing, substrate oxygen concentration (measured with O 2

electrode) was 3 mg dm−3. The treatment solutions were replaced thereafter

weekly till harvesting and in hypoxic treatments the new solution was flushed

with N2 for 15 minutes to remove oxygen.

Growth Measurement

To study leaf expansion (increase in leaf length) 2-day old leaf of each plant

from shoot apex was marked and leaf length was measured at 2 day (d) interval

up to 11th day. After 8 weeks of salinity and hypoxia stress plant height was

recorded. At this time plants were harvested and their dry weights of shoots

and roots were recorded after oven drying the samples at 70◦C in a vacuum

oven for 48 hrs.

Leaf Ionic Analysis

Plants were harvested after 8 weeks and leaves of plants were divided into top

leaves (young leaves) and lower fully expanded leaves (mature leaves). The


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separated leaves were immediately washed with distilled water and blotted dry

with tissue paper. The samples were then dried at 70◦C in a forced air driven

oven for 48 h. The oven dried plant samples were fine ground in a wily mill topass through 1 mm sieve. The fine ground plant samples (1 g) were digested in

tri-acid mixture (sulfuric acid, nitric acid, and perchloric acid) (Miller, 1998).

Potassium and Na+ were determined on a flame photometer (Jenway PFP-

7, Bibby Scientific LTD., Essex England). For chloride determination, plant

samples were extracted with HNO3 and chloride was determined from this

extract using chloride analyzer (Corning Chloride Analyzer 926, Corning Inc.,

Corning, NY, USA).

Statistical Analysis

The data were analyzed statistically following the methods of Gomez and

Gomez (1984) using MSTAT-C (Russell and Eisensmith, 1983). The signif-

icance of differences among the means was compared using standard error

computed as s/√ n, where s is the standard deviation and n shows the number

of observations.

RESULTS

Shoot and Root Growth

Salinity significantly reduced shoot dry matter of all the species at both non-

hypoxic and hypoxic conditions (Figure 1). E. camaldulensis (Silverton) pro-

duced the maximum absolute and relative shoot dry matter (36%) under non-

hypoxic salinity followed by E. camaldulensis (Local) and E. tereticornis.

However, under hypoxic salinity treatment E. camaldulensis (Local) performed

best followed by E. camaldulensis (Silverton) and E. tereticornis, in absolute

as well as relative terms. Hypoxia alone reduced the shoot and root dry matter

of E. tereticornis only. Root dry matter (RDM) of Eucalyptus species was also

significantly reduced by salinity in hypoxic conditions (Figure 2). E. camal-

dulensis (Local) and E. tereticornis produced respectively, the maximum and

minimum root dry matter in this treatment. However, in non-hypoxic salinity

treatment E. camaldulensis (Silverten) and E. camaldulensis (Local) differed

non-significantly. Root: shoot ratio (RSR) of Eucalyptus species was increased

significantly under saline conditions both in hypoxic and non-hypoxic treat-

ments, whereas hypoxia alone did not affect it significantly (data not shown).

Salinity also significantly reduced leaf expansion of E. tereticornis and E.

camaldulensis (Local) under non-hypoxic as well as hypoxic conditions (Fig-

ure 3). Plant height of all the species was also reduced significantly by salinity

and salinity × hypoxia (data not shown).


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Figure 1. Shoot dry matter (g/plant) of Eucalyptus species grown with salinity and

hypoxia. The columns show mean of 5 replications and bars show standard error.

Salinity level for saline treatment was 150 mol m−

3 NaCl. Plants were grown for 8

weeks in the treatment solutions.

Figure 2. Root dry matter (g/plant) of Eucalyptus species grown with salinity and

hypoxia. The columns show mean of 5 replications and bars show standard error.

Salinity level for saline treatment was 150 mol m−3 NaCl. Plants were grown for 8

weeks in the treatment solutions.


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Figure 3. Leaf expansion (cm/d) of Eucalyptus species grown with salinity and hy-

poxia. The columns show mean of 5 replications and bars show standard error. Salinity

level for saline treatment was 150 mol m−3 NaCl. Plants were grown for 8 weeks in the

treatment solutions.

Leaf Ionic Composition

Leaf ionic composition of young as well as mature leaves was significantly

affected by salinity under non-hypoxic as well as hypoxic conditions with a

similar trend in both types of the leaves (Figures 4–6; data shown only for

the young leaves). Salinity caused a significant increase in Na+ and Cl− con-

centrations in both type of the leaves irrespective of the hypoxic treatment(Figures 4 and 5). Sodium concentration in young leaves of plants grown with

salinity was 3.5 folds and 4.5 folds higher than those grown without salinity

under non-hypoxic and hypoxic conditions, respectively. E. tereticornis and E.

camaldulensis (Silverton) accumulated the maximum Na+ under non-hypoxic

saline treatment and differed non-significantly. E. camaldulensis (Local) accu-

mulated the minimum leaf Na+ in both the saline treatments. Leaf Na+ was

also significantly higher in the leaves of all the species under hypoxic salinity

treatment than under non-hypoxic salinity treatment. The maximum chloride

(Cl−) concentration was observed in the leaves of E. camaldulensis (Silverton)under non-hypoxic salinity and in the leaves of E. tereticornis under hypoxic

salinity treatment. E. camaldulensis (Local) differed non-significantly with E.

camaldulensis (Silverton) under hypoxic saline conditions and with E. tereti-

cornis under non-hypoxic saline conditions. Potassium sodium ratio (K+ : Na+

ratio) was significantly decreased due to salinity stress in the root environment


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Figure 4. Sodium concentration (mmoles kg−1) in young leaves of Eucalyptus species

grown with salinity and hypoxia. The columns show means of 5 replications and bars

show standard error. Salinity level for saline treatment was 150 mol m−3 NaCl. Plants

were grown for 8 weeks in the treatment solutions.

Figure 5. Chloride concentration (mmoles kg−1) in young leaves of Eucalyptus species

grown with salinity and hypoxia. The columns show means of 5 replications and bars

show standard error. Salinity level for saline treatment was 150 mol m−3 NaCl. Plants

were grown for 8 weeks in the treatment solutions.


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Figure 6. K:Na in young Leaves of Eucalyptus species grown with salinity and hy-

poxia. The columns show means of 5 replications and bars show standard error. Salinity

level for saline treatment was 150 mol m−3 NaCl. Plants were grown for 8 weeks in the

treatment solutions.

under hypoxic as well as non-hypoxic conditions (Figure 6). The maximum

K+: Na+ ratio was observed in E. camaldulensis (Local) followed by E. camal-

dulensis (Silverton) under both non-hypoxic and hypoxic salinity treatments.

Salinity under hypoxic conditions also have a significantly higher effect than

under non-hypoxic conditions whereas hypoxia alone significantly decreased

the leaf K+

: Na+

of E. tereticornis only.

DISCUSSION

Sodium chloride salinity in the nutrient solution significantly reduced tree

growth in terms of plant height, leaf expansion, shoot dry matter, and root dry

matter in all the species (Figures 1–3) and there was a negative significant

correlation between growth performance and leaf Na+ and Cl− concentrations

(Table 1). Water stress, ion imbalance and ion toxicity are considered thecommon causes of growth reduction due to salinity (Munns, 2002; 2005; Zhu,

2003). Genotypic differences for different growth parameters were significant

among the three species in non-hypoxic saline treatment. In this treatment, E.

camaldulensis (Silverton) and E. camaldulensis (Local) produced higher shoot

and root dry matter than E. tereticornis but differed non-significantly with one


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Table 1

Relationship between different growth parameters and ionic composition of young and

mature leaves of Eucalyptus species

Shoot dry matter Root dry matter Leaf expansion

Na+ in young leaves −0.71∗∗ −0.60∗ −0.39NS

K+ in young leaves 0.51∗ 0.72∗ 0.47∗

K+ :Na+ in young leaves 0.82∗∗ 0.79∗∗ 0.61∗

Cl− in young leaves −0.69∗ −0.63∗ −0.47∗

another. The poor growth performance of E. tereticornis may be due to higher

Na+ and Cl− uptake, lower K+ uptake (Table 2) and resultantly low K+ : Na+

ratio in its leaves. The leaf Na+ concentration of E. camaldulensis (Silverton)

was statistically similar to E. tereticornis but its better growth shows better

compartmentalization of Na+ and Cl− into the vacuoles by this species. The

higher K+ : Na+ ratio also supports its higher growth performance (Rezaei et

al., 2006). Saqib et al. (2005b) reported that better compartmentalization of

Na+ into the vacuoles is an important determinant for salt tolerance in wheat.

Lower Na+ and Cl− accumulation by E. Camaldulensis (Local) shows better

exclusion in this species at the root level (Table 2; Na+ and Cl− uptake per g

root dry matter) that enabled its better growth (Saqib et al., 2004a). A number of

Table 2

Sodium and chloride uptake (mg per g root dry matter) by different Eucalyptus

species under saline and saline hypoxic conditions

Non-hypoxic saline Hypoxic saline

Sodium uptake E. tereticornis 3.8 3.2

E. camaldulensis (Silverton) 2.9 2.8

E. camaldulensis (Local) 1.4 2.3

Chloride uptake

E. tereticornis 1.6 2.0

E. camaldulensis (Silverton) 1.3 1.4

E. camaldulensis (Local) 1.1 1.7

Potassium uptake

E. tereticornis 0.95 0.76

E. camaldulensis (Silverton) 1.0 0.69 E. camaldulensis (Local) 1.0 1.4

The columns show mean of 5 replications and bars show standard error.

Salinity level for saline treatment was 150 mol m−3 NaCl. Plants were grown

for 8 weeks in the treatment solutions.


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researchers have reported significant variations in the growth and salt tolerance

among different species of the woody plants (Bell et al., 1994; Marcar et al.,

1995; Rawat and Banerjee, 1998). Many earlier researchers have used Na+ :K+ ratio as an indicator of salinity tolerance (Saqib et al., 2004b; Munns, 2005;

Rezaei et al., 2006) as adequate Na+ : K+ ratio in the cytosol is essential for

normal cellular functions of plants (Marschner, 1995; Chinnusamy et al., 2005).

Higher levels of external Na+ in saline soils interfere with K+ acquisition by

plants (Subbarao et al., 1990). The species with ability to maintain K+ uptake

or to exclude Na+ can tolerate salinity stress such as E. camaldulensis (local).

The lower Na+ uptake and higher K+ uptake at root level, and higher K+ :

Na+ ratio in this species is in accordance with its better performance at saline

environment (Table 2; Figure 6).Low oxygen supply in hypoxia affects root growth because energy pro-

duction is decreased (Barret-Lennard, 1986). Under hypoxia, shoot and root

growth retardation has also been reported by several researchers (Jackson,

1979; Lizaso et al., 2001). In the present study, hypoxia significantly reduced

the shoot and root growth of the salt sensitive species E. tereticornis only (Fig-

ures 1-2). Aerenchyma development in the roots is an important mechanism of

hypoxia tolerant (Saqib et al., 2005a) that may not have developed considerably

in this species. Marcar et al. (1995) also observed large variations among the

eucalyptus species for their tolerance to oxygen deficiency (waterlogging). Insaline-hypoxic conditions roots are not able to exclude Na+ and Cl− mainly

because of low energy production (Qureshi and Barret-Lennard, 1998). This

lower ability to exclude toxic elements can further inhibit K+ uptake by plant

roots. Saqib et al. (2004a) reported a higher accumulation of Na+ and Cl− and

lower K+ in leaf sap under saline waterlogged conditions than under saline

conditions. Marcar et al. (1993) and Galloway and Davidson (1993) observed

similar depressive effects of salinity × hypoxia interaction on growth of Euca-

lyptus and Atriplexes.

However, in the present study higher reduction in shoot and root growthwas observed only in E. camaldulensis (Silverton) in saline hypoxic treatment

than in the non-hypoxic saline treatment (Figures 1–2). It may be due to its

decreased root ability to develop aerenchyma that resulted in low Na+ exclusion

and K+ uptake at the root level (Figure 4; Table 2) as aerenchyma helps in root

Na+ exclusion (Saqib et al., 2005b). In this treatment E. camaldulensis (local)

performed significantly better than the other species which may be due to its

better aerenchyma and nodal root development and hence better salt exclusion

at the root level. In conclusion, E. camaldulensis (Silverton) is better tolerant

to salinity alone and E. camaldulensis (local) is better tolerant to saline andhypoxic conditions. E. camaldulensis (Silverton) seems to have better tissue

compartmentalization whereas E. camaldulensis (local) seems to have better

exclusion of Na+ at the root level.


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Salinty n Hypoxia Interaction in Eucalptus

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