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for CSIRO andthe Australian Academy of ScienceAust. J. Bot., 2000, 48, 455–460

Effects of sodium chloride on seed germination and growth of two
Chinese desert shrubs, Haloxylon ammodendron and H. persicum(Chenopodiaceae)
Kazuo TobeAD, Xiaoming LiB and Kenji OmasaAC
A

Environmental Biology Division, National Institute for Environmental Studies, 16-2, Onogawa,
Tsukuba, Ibaraki 305-0053, Japan.
B
Xinjiang Institute of Biology, Pedology and Desert Research, Chinese Academy of Sciences,
No. 40, South Beijing Road, Urumqi, Xinjiang 830011, P. R. China.
C
Present address: Graduate School of Agricultural and Life Sciences, University of Tokyo,
Yayoi 1-1-1, Bunkyo, Tokyo 113-8657, Japan.
D
Corresponding author; email: tobe@nies.go.jp

Abstract. The effects of sodium chloride (NaCl), polyethylene glycol-6000, temperature and light on germination andthe effects of NaCl on growth were investigated in two Chinese desert shrubs, Haloxylon ammodendron (C.A.Mey.)
Bunge and H. persicum Bunge ex Boiss. et Buhse. Both species occur in non-saline sand dunes; H. ammodendron also
occurs in saline land, although it is not dominant there. Percentage germination of H. ammodendron and H. persicum in–3.0 MPa (667 mmol kg–1) NaCl was 91 and 64%, respectively. Hydroponic culture of each species for c. 3 months with
NaCl solutions of 0, 200, 400 and 600 mmol kg–1 showed that the survival of H. ammodendron was highest (82.3%) at
400 mmol kg–1 NaCl, while that of H. persicum decreased with increasing NaCl concentration and was low (11.1%) at
400 mmol kg–1 NaCl. Sodium concentration in shoot tissues of 99-day-old seedlings grown at 400 mmol kg–1 NaCl
exceeded 1000 mmol kg–1 in both species, while Na concentration in non-transpiring young seedlings grown in
400 mmol kg–1 NaCl was 240 and 350 mmol kg–1 for H. ammodendron and H. persicum, respectively. The results indicate that both species have relatively low adaptability to salinity at the older seedling stage compared with that at the germination and young seedling stage, and that H. ammodendron shows higher adaptability to salinity at the older seedlingstage than H. persicum. It was concluded that salinity adaptability in the later developmental stage of these species
determines their distribution with respect to salinity.
Introduction
In order for plants to become established in saline environments, adaptation at both the germination and mature stage iscrucial (Ungar 1991, 1995). There have been many studies on
the effects of salinity at both the germination and later developmental stages (e.g. West and Taylor 1981; Stumpf et al.
1986; Partridge and Wilson 1987; Ungar 1996). However, it
is still unclear how adaptation to salinity at different developmental stages is correlated with the distribution of species inlocations with different degrees of salinity (Ungar 1991). It isalso unclear how salt accumulation in plant tissues is related toadaptation of species to salinity.
Haloxylon ammodendron (C.A.Mey.) Bunge and H. persicum
Bunge ex Boiss. et Buhse (Chenopodiaceae) are shrubs foundin desert regions of north-western China (Fu and Jin 1992).
Haloxylon ammodendron occurs on both saline and nonsaline lands, although it is not a dominant species on saline
land. In contrast, H. persicum is found only on non-saline
land. In both species, the leaves are very small and the green
branches photosynthesise. The seeds of these species have no© CSIRO 2000

endosperm and only a fully differentiated spiral seedlingcoated by pericarp. The germination process of this type ofseed seems to consist simply of water absorption by the dry
spiral seedling and its subsequent stretching (Wallace et al.
1968; Sharma and Sen 1989). In China, both species serve as
livestock feed and firewood, and are also planted in sanddunes to stabilise them (Fu and Jin 1992).
It is unclear why only H. ammodendron occurs on salineland, while H. persicum is limited to non-saline land. The
present study was undertaken to investigate at what developmental stage their geographical distribution is determined.
Because sodium chloride (NaCl) is the most abundant salt inmany salinised locations in Chinese desert (Fan et al. 1993),
it was used to examine the responses of plants to salinity. We
examined the effects of moistening with polyethylene glycol(PEG)-6000 and NaCl solutions on the germination of these
two species. Seed longevity, responses of germination totemperature and light were also examined because thesefactors determine the time and locations of germination, andcould affect the feature of responses of seeds to salinity. The
10.1071/BT99013

0067-1924/00/040455

456

K. Tobe et al.

effects of NaCl on survival and growth of transpiring older
seedlings were also investigated. Additionally, ion concentrations in plants treated with different concentrations of
NaCl were examined in both non-transpiring young
seedlings and shoots of transpiring older seedlings.
Materials and methods
Seeds
Seeds of H. ammodendron (seed weight: (mean ± s.e.) 3.48 ± 0.48 mg;
n = 20) and H. persicum (seed weight: (mean ± s.e.) 5.89 ± 0.87 mg,
n = 20) were collected soon after ripening in November of 1995 and1997 from plants growing in a non-saline location in the Turpan
Botanical Garden of the Xinjiang Institute of Pedology, Biology andDesert Research, Turpan, China (42°56⬘N, 89°2⬘E) and irrigated regularly. The collected seeds were initially stored at c. 5°C until transport toJapan in the following January or March. After transport to Japan, mostof the seeds were stored at c. –18°C to avoid loss of germinability, andthe germination experiments were carried out within 12 months after the
ripening of the seeds; some seeds were stored either at c. 23°C for
11 months or at c. 2°C or c. –18°C for 23 months to examine theirlongevity at different temperatures.
Experiments at germination and young seedling stage
In all the experiments on germination and young seedling stage,
25 seeds were sown in 90-mm Petri dishes on three layers of filter paper(Toyo, No.1) moistened with 10 mL of deionised water or a solution of
NaCl or PEG-6000. The Petri dishes were covered with lids and maintained at a constant temperature in an incubator. About two-thirds of thevolume of the water or solution in each Petri dish was replaced daily to
avoid change in the ΨW of the solution. The seeds were considered tohave germinated when the emerging seedlings had almost completely
uncoiled and elongated to a length exceeding 10 mm.
(a) Seed longevity
Seeds stored at different temperatures for 11 or 23 months were moistened with deionised water and maintained at 20°C in darkness for 10 days.
Seed viability was evaluated by the final percentage germination.
(b) Effects of temperature and light on seed germination
Seeds were moistened with deionised water and maintained at a constant temperature (5–35°C) in either under continuous darkness or continuous illumination with fluorescent lamps (photon flux density at thesurface of the seeds: 80–90 ␮mol m–2s–1 over the waveband 400–700 nm)
for 10 days.
(c) Effects of NaCl and PEG on seed germination
Seeds were moistened with either deionised water or a NaCl or PEG6000 solution of a known water potential (ΨW) between –1.0 and –6.0
MPa and maintained at 20°C in continuous darkness for 21 days. NaClsolutions of known ΨW were prepared according to Lang (1967).
Solutions of PEG-6000 were prepared so that each was almost isotonic

with the corresponding NaCl solution; the ΨW of the PEG solutions wasdetermined with an isopiestic psychrometer (Boyer and Knipling 1965)
at 20°C with NaCl solutions of known ΨW as standards.
(d) Na and K concentrations in young seedlings
Sodium and potassium concentrations in young seedlings were measured after moistening the seeds with water or a solution of NaCl (200,400, or 600 mmol kg–1) for 1–3 days, until they had germinated and theseedlings had elongated to a length of c. 20 mm; thereafter, 40–60
seedlings were blotted dry and quickly weighed, dipped into water andquickly blotted dry again to remove salt on their surface, and dried at
80°C for more than 3 days. After determining the dry weights of theseedlings, they were ground, decomposed with HNO3 on a hot plate, andfinally dissolved in a 100-mL aqueous solution, which was analysed for
Na and K content by ICP spectrometry (ICAP-750, Nippon Jarrell-Ash,
Japan). From the results, Na and K concentrations expressed on a tissue
water basis were calculated.
Experiments at older seedling stage
Experiments were carried out in a greenhouse (temperature, 25°C; relative humidity, 60%). Each species was grown in wet coarse sand for the
first week after sowing the seeds; thereafter, seedlings with a height of
50–70 mm were transferred to four 15-L tanks filled with a nutrient solution (6 mmol kg–1 KNO3, 4 mmol kg–1 Ca(NO3)2, 4 mmol kg–1
NH4H2PO4, 2 mmol kg–1 MgSO4, 54 ␮mol kg–1 Fe-EDTA, 46 ␮mol kg–1
H3BO3, 9.1 ␮mol kg–1 MnCl2, 0.32 ␮mol kg–1 CuSO4, 0.76 ␮mol kg–1
ZnSO4, 0.56 ␮mol kg–1 Na2MoO4), so that the roots were immersed in
the solution. Seventeen or 18 seedlings each of the two species weretransferred to each tank. One week after the transfer, NaCl was added
daily for 1 week to three of the tanks so that their final NaCl concentrations became 0, 200, 400, or 600 mmol kg–1; these NaCl concentrations
were maintained throughout the experimental period. The solution ineach tank was aerated and renewed once a week. Dead plants andbranches were removed. In this study, plants were regarded as deadwhen most parts of their green branches had died. Ninety-nine days aftersowing, the surviving plants were harvested and the fresh weights ofroots and shoots were determined. Dry weights of the roots and shoots
were measured after oven-drying at 80°C for more than 3 days. Sodium
and potassium concentrations expressed on a tissue water basis in theshoots were determined in some of shoot samples by the method
described above.

Results
Seed longevity and effects of temperature and lighton seed germination
Percentage germination of seeds stored at c. 2 or c. –18°C for
23 months exceeded 90% in both species. However, percentage germination of seeds stored at c. 23°C for 11 months was
20 ± 7.1% and 3 ± 1.0% (mean ± s.e.) for H. ammodendronand H. persicum, respectively.

Table 1. Effects of temperature on percentage germination in two Haloxylon species
Seeds were moistened with deionised water for 10 days in continuous darkness. Data are means of four replications ± s.e.
Species
Haloxylon
ammodendron
H. persicum

Percentage germination (%) at
15°C
20°C

5°C

10°C

96 ± 3.3

100 ± 0.0

100 ± 0.0

95 ± 3.8

96 ± 3.3

95 ± 3.8

25°C

30°C

35°C

98 ± 2.3

93 ± 6.0

91 ± 2.0

54 ± 8.3

95 ± 2.2

81 ± 8.959 ± 8.932 ± 9.2

NaCl effects on germination and growth457

Effects of temperature on the germination was examined(Table 1). For both species, percentage germination exceeded
50% within 1 day after moistening at temperatures of
15–30°C; however, at 5 and 10°C, percentage germination ofboth species exceeded 50% after 2 and 3 days, respectively(data not provided). The final percentage germination of both
species exceeded 50% at temperatures below 30°C (Table 1).
For both species, the effect of light illumination on germination was not significant under any temperature regime(Student’s t-test; P = 0.05) (data not provided).
Effects of NaCl and PEG on seed germination
Because both the final percentage germination and germination rate were high at 20°C in both species in the above experiment, the optimal germination temperature can be regarded
to be near at 20°C; therefore, effects of NaCl and PEG on
seed germination were examined at 20°C.
When the seeds were moistened with solutions of NaCl or
PEG, germination in both species was retarded as the ΨWdecreased: percentage germination after 1 and 2 days wasconsiderably decreased with decreasing ΨW in both species
in both treatments. (Fig. 1). In NaCl treatment, the final percentage germination was not conspicuously changed withchanging ΨW at ΨW higher than –3.0 MPa (H. ammodendron)or –2.0 MPa (H. persicum); but it decreased considerably withdecreasing ΨW at lower ΨW (Fig. 2). The final percentage germination of PEG-treated seeds was high at ΨW higher than
–1.9 MPa (H. ammodendron) or –0.9 MPa (H. persicum); but
at lower ΨW, it decreased with decreasing ΨW, and was
almost zero for both species when ΨW was lower than
–4.1 MPa (Fig. 2). For the NaCl treatment, the final percentage germination was higher between –3.0 and –6.0 MPa in
H. ammodendron than in H. persicum (Fig. 2). The final percentage germination of seeds treated with PEG solutions of–1.9 and –3.1 MPa was lower in H. persicum than in
H. ammodendron. The inhibitory effect on germination wasconsiderably less for both species in NaCl than in isotonic
PEG solutions (Fig. 2).
Although seedling elongation in both species was considerably slower with decreasing ΨW of the solution for both the
NaCl and PEG treatments, the emerging seedlings continued
to elongate until their length exceeded 10 mm (data not provided). Furthermore, no visible evidence was detected of any
injurious or toxic effects on the seedlings from the NaCl or
PEG solutions.

tration in the external medium (Fig. 3) because of the increasing duration of exposure of the seedlings to water or solutions
and resultant more leakage of K from them. Both the increasein Na concentration and the decrease in K concentration in theseedlings with increasing external NaCl concentration weremore pronounced in H. persicum than in H. ammodendron.

Concentrations of Na and K in young seedlings

Effect of NaCl on growth and ion concentrations in shoots

When seeds were moistened with either water or a solution ofNaCl, the time taken by the emerging seedlings to reach alength of c. 20 mm became longer as the NaCl concentrationin the external medium increased (data not provided).
As the external NaCl concentration increased, Na concentration in the seedlings increased in both species (Fig. 3). The
concentration of K decreased with increasing NaCl concen-

When hydroponically cultivated, the branches of all plants
treated with NaCl (200–600 mmol kg–1) became succulent(branch diameter 2.0–3.0 mm) in both species, while thebranches of all plants that were not treated with NaCl
(0 mmol kg–1) remained non-succulent (branch diameter
1.0–1.5 mm). Some plants in both species died (Table 2); forboth species, shoot death preceded the death of the roots.

Fig. 1. Changes over time in percentage germination in the initial
10 days when the seeds were moistened with deionised water (䊊), a
NaCl solution of –1.0 MPa (223 mmol kg–1) (䊐), –2.0 MPa (446 mmolkg–1) (䉭), –3.0 MPa (667 mmol kg–1) (䉫), –4.0 MPa (883 mmol kg–1)(×) or –5.0 MPa (1095 mmol kg–1) (+) or a PEG solution of –0.9 MPa(䊏), –1.9 MPa (䉱), –3.0 MPa (䉬) in continuous darkness at 20°C. Eachpoint represents the mean of four replications.

458

K. Tobe et al.

shoots continued to increase beyond 200 mmol kg–1 external
NaCl concentration, whereas that of H. ammodendron shootsremained at about 1000 mmol kg–1 in external NaCl concentrations of 200–600 mmol kg–1 (Fig. 4). In both species,
K concentration decreased when external NaCl concentration increased from 0 to 200 mmol kg–1, but did not show
marked changes with changing external NaCl concentration
at higher external NaCl levels.

Fig. 2. Percentage germination 21 days after moistening seeds of
H. ammodendron (䊊, 䊉) and H. persicum (䊐, 䊏) with deionised water(at 0 MPa), or NaCl (䊊, 䊐) or PEG (䊉, 䊏) solutions with different ΨW(water potential) in continuous darkness at 20°C. Corresponding NaCl
concentration is shown in the legend of Fig. 1. Each point represents themean of four replications; error bars indicating s.e. are shown only
where s.e. was larger than point size.

Fig. 3. Sodium (䊉, 䊏) and potassium (䊊, 䊐) concentrations in c. 20mm-long seedlings of H. ammodendron (䊊, 䊉) and H. persicum (䊐, 䊏)
as a function of the NaCl concentration in the external medium in which
the seeds were germinated at 20°C. Each point represents the mean offive replications; error bars indicating s.e. are shown only where s.e. waslarger than point size.

Marked differences in response to NaCl between
H. ammodendron and H. persicum were detected (Table 2).
While H. ammodendron showed highest survival at 400 mmol
kg–1 NaCl, survival of H. persicum decreased with increasing
NaCl concentration and was zero at 600 mmol kg–1 NaCl
(Table 2). Highest mean dry weight of surviving plants was
between 200 and 400 mmol kg–1 NaCl for H. ammodendron
and at 200 mmol kg–1 NaCl in H. persicum in both shoots androots (Table 2).
In 0 mmol kg–1 NaCl treatment, the mean Na concentration of H. ammodendron was about nine times higher thanthat of H. persicum. Sodium concentration in H. persicum

Discussion
In typical habitats of these species in China, annual precipitation is c. 200 mm or less; monthly mean temperature is lower
than 0°C from November to March and 23 to 27°C from June toAugust (Fu and Jin 1992). Measurement of Na content in 0–0.5
m deep soil layer in saline locations where H. ammodendron
was distributed showed that Na content at four sites ranged
between 29 and 311 mmol (kg dry soil)–1 (X. Li, unpubl.
data). Precipitation from late November to early March isusually as snow, which covers the ground in these regions
during winter, and melting snow in the early spring leaches
salt from the surface in saline locations and supplies
water to the seeds, causing their germination. On summerdays, the ground surface temperature rises to 60–80°C(Fu and Jin 1992).
Seeds of both H. ammodendron and H. persicum lost mostof their germinability within 11 months when they were stored
at c. 23°C, i.e. at a high temperature, but at temperatures lower
than c. 2°C, their germinability was maintained for 23 months.
These results concur with the fact that, in typical habitats ofthese species in China, the seeds ripen in November, overwinter without significant decline in germinability, and germinate
with sufficient water supply after winter; however, in the hot
season, very high soil temperatures would cause loss of theirgerminability more rapidly than did storage at c. 23°C. Thus,
for these short-lived seeds, rapid germination and low dependence of germination on environmental conditions would
prevent loss of germinability before germination and increase
the possibility of establishment.
In many saline environments, viability of seeds in hypersalinity is one of the important factors in determining whether
a species occurs in saline environments (Ungar 1991, 1995).
However, this factor would not limit the distribution of these
species in saline environments: the best chance of germinationof these species would be spring in the year following ripening;from ripening to early spring, the seeds of these species are notmoistened with saline solution because of the cold climate.
For both species tested, the percentage germination in
NaCl was significantly higher than that in isotonic PEG solutions. This would be due to NaCl movement into theseedlings (Fig. 3). When NaCl enters the seeds, it decreases
the ΨW in the seeds and promotes water uptake by them.
Seeds that germinate better in NaCl than in isotonic PEG
solutions have been reported for some other species (Sharma
1973; Romo and Eddleman 1985; Tobe et al. 1999).

459

NaCl effects on germination and growth

Table 2. Percentage survival and shoot and root dry weight of plants grown at different NaCl concentrations
Dry weight was measured only for survived plants. In each column, the values followed by the same letter are not significantly
different from each other at P = 0.05 (Student’s t-test)
External NaCl
concentration(mmol kg–1)

0
200
400
600

H. ammodendron
Percentage
survival (%)
47.1
64.7
82.3
23.5

H. persicum

Dry weight (mg)
Shoot

Root

704ab
1053a
1165a
542b

87a
103a
142a
126a

The ΨW of the NaCl solution that inhibited germination ofboth H. ammodendron and H. persicum was rather low compared with those that inhibit germination of many halophytic
species (Partridge and Wilson 1987; Myers and Morgan
1989; Khan and Rizvi 1994; Khan and Ungar 1996; Ungar
1996). For example, the seeds of two tested species germinated in an NaCl concentration about twice the maximum
possible for seeds of a halophyte Haloxylon recurvum (Khanand Ungar 1996). It is unlikely, that the higher percentage
germination of H. ammodendron than H. persicum in NaClsolutions of ΨW lower than –3.0 MPa determines their geographical distribution. Moreover, the seedlings emerging athigh salinity continued to elongate without any detectablesigns of injurious or toxic effects of NaCl. These results showthat both H. ammodendron and H. persicum are well adapted
to highly saline environments at the germination and young
seedling stage.
The adverse effects of NaCl were more conspicuous in theolder seedling stage in both species (Table 2). This would be
associated with the considerably higher Na concentration in
the shoots of transpiring plants (Fig. 4) than in the non-transpiring small seedlings (Fig. 3) grown at the same external
NaCl concentration. This would be because transpiration
stream causes continuous salt transport to plant tissues. The
Na concentrations in the shoots (Fig. 4) were higher thanthose reported for many halophytes grown under comparable
NaCl concentrations (Jefferies et al. 1979; Neales andSharkey 1981; Esel 1985; Robinson and Downton 1985;
Demmig and Winter 1986; Matoh et al. 1988). Na concentrations in the shoots of these halophytes grown at 400–600
mmol kg–1 were within a range 100–800 mmol kg–1, whilethat in the shoots of two tested species grown at 400–600
mmol kg–1 exceeded 1000 mmol kg–1 (Fig. 4). Maintaining a
low internal accumulation of salt is an important strategy forplants to survive in saline environments (Clemens et al. 1983;
Luard and El-Lakany 1984; Aswathappa and Bachelard
1986; Matoh et al. 1988). The higher salt accumulation in
the shoot of both species may be related to the fact thatneither species is dominant in saline environments. Ourfindings that NaCl in the root medium causes succulence andPercentage
survival (%)
83.3
44.4
11.1
0

Dry weight (mg)
Shoot

Root

500a
768a
210a
—

90a
100a
44a
—

decreased K concentration are in accord with the results ofprevious research (Handley and Jennings 1977; Neales andSharkey 1981; Esel 1985; Robinson and Downton 1985;
Demmig and Winter 1986).
NaCl caused more adverse effects on H. persicum than on
H. ammodendron in the older seedling stage (Table 2). This
would explain why H. persicum is excluded from saline locations. Haloxylon ammodendron appears to be better able toregulate its internal Na concentration. Indeed, the Na concentration in the shoot of this species was considerably higher
than that in H. persicum at 0 mmol kg–1 (Fig. 4), and was
almost constant in the range of 200–600 mmol kg–1 (Fig. 4).
We conclude that salinity adaptability in the older seedlingstage of the tested species is correlated with their geographical distribution with respect to salinity.

Fig. 4. Sodium (䊉, 䊏) and potassium (䊊, 䊐) concentrations inshoots of H. ammodendron (䊊, 䊉) and H. persicum (䊐, 䊏) as a function of NaCl concentration in the root medium. Each point represents
the mean of five replications except for 600 mmol kg–1 NaCl-treated
H. ammodendron (n = 4) and 400 mmol kg–1 NaCl-treated H. persicum(n = 2). Error bars indicating s.e. are shown only where the s.e. waslarger than point size.

460

K. Tobe et al.

Acknowledgments
We thank Dr Nishikawa and Ms Kumada for analysing the Na
and K concentrations of the plant samples of H. ammodendronand H. persicum by ICP spectrometry.
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Manuscript received 9 March 1999, accepted 28 July 1999

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