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Australian Journal of Botany, 2005, 53, 529–534

Effects of irrigation on seedling emergence and seedling survival ofa desert shrub Haloxylon ammodendron (Chenopodiaceae)
Kazuo TobeA,D , Xiaoming LiB and Kenji OmasaC
A Laboratory of Intellectual Fundamentals for Environmental Studies, National Institutefor Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
B School of Environmental Science and Engineering, Shandong University, No. 27,

South Shada Road, Jinan 250100, P.R. China.
C Graduate School of Agriculture and Life Sciences, The University of Tokyo, Yayoi 1-1-1,

Bunkyo-ku, Tokyo 113-8657, Japan.
D Corresponding author. Email: tobe@nies.go.jp

Abstract. Haloxylon ammodendron (C.A. Mey) Bunge (Chenopodiaceae) is a shrub occurring on desert sanddunes in China. Seedling emergence and seedling survival were investigated by sowing seeds at different depths(0, 2.5, 5.0 or 10 mm) in ﬁne or coarse sand in pots irrigated under different regimes. Seed burial in sand was required
for seedling establishment of this species. Seedling emergence depended greatly on seed burial depth, sand type,and irrigation regime; this appeared to be due to (1) seeds or seedlings suffering from oxygen or moisture deﬁciency
depending on the air : moisture ratio in sand, and/or (2) higher moisture content in sand resulting in hardening of
the sand and obstruction of seedling growth. Increased irrigation resulted in longer survival of emerging seedlings
because sand was moistened more deeply, and moisture in deeper sand persisted longer. The results suggest thatthe infrequent and light precipitation common in desert environments is likely to cause germination of many of theburied seeds, but is insufﬁcient for emerging seedlings to survive. It is suggested that water from melting snow inearly spring is crucial in enabling seedling establishment of this species in the deserts of China.

Introduction
Haloxylon ammodendron is a shrub that occurs in thewestern deserts of China (Walter and Box 1983; Fu andJin 1992). This species is commonly found on stable sanddunes, although it also occurs on salinised areas (Tobeet al. 2000a). Seeds of this species have no endospermand have only a fully differentiated spiral embryo enclosed
by pericarp. The germination process of this type of seedconsists simply of water absorption by the dry spiralembryo and subsequent elongation (Wallace et al. 1968;
Sharma and Sen 1989).
In a previous paper (Tobe et al. 2000a), we reported thatfor H. ammodendron seeds (1) germination after irrigation
was very rapid; (2) germination showed low or no dependence
on seed dormancy, temperature, light, or the water potentialof the substrate; and (3) seeds were short-lived and were
expected to lose viability in the ﬁeld within one yearof maturation. In the present study, we investigated thecharacteristics of seedling emergence from sand and seedlingsurvival in this species.
Moisture content in sand depends not only on thefrequency and amount of water supplied, but also on sand
© CSIRO 2005

depth (Tobe et al. 2005). While moisture in sand near thesurface evaporates quickly, moisture in deeper sand persists
longer because of a lower evaporation rate. By contrast, an
increase in the volume of moisture in sand causes a decreasein the volume of air, and this may result in oxygen deﬁciency
for germinating seeds or growing seedlings. Because areduction in oxygen availability inhibits seed germination
and/or seedling growth (Gill and Miller 1956; VanderZeeand Kennedy 1981; Crawford 1992), the air : moisture ratio
in sand, as well as the moisture content itself, may be factorsthat affect seedling emergence. In addition, moisture in sandcauses hardening of sand (Krumbein 1959; Hornbaker et al.
1997) and may cause mechanical resistance to seedling
growth (Tobe et al. 2005). Therefore, because seeds located at
different depths in sand are exposed to different moisture andoxygen conditions and sand hardness after water is supplied,
seed germination and seedling emergence are expected to beaffected by both the depth of seed burial in sand and theamount of water supplied.
This study was undertaken to investigate the effects of seedburial depth in sand and irrigation on seedling establishmentof H. ammodendron. We examined the emergence and10.1071/BT04210

0067-1924/05/060529

530

Australian Journal of Botanysurvival of seedlings when seeds were sown at different
depths in sand and irrigated under different regimes. For theexperiments, we used ﬁne sand, the particle-size distributionof which was similar to that of sand dunes in China, but
in some experiments, coarse sand was used to examine theeffect of well draining sand with high air : moisture ratio on
seedling emergence.
Materials and methods
Seeds
Seeds of Haloxylon ammodendron (mean seed weight: 3.48 mg) werecollected soon after maturation in November 2001 from plants growing
in the Tulufan Botanical Garden of the Xinjiang Institute of Pedology,
Biology and Desert Research, Tulufan, China (42◦ 56 N, 89◦ 12 E).
The collected seeds were initially stored at room temperature until
transported to Japan in January 2002. In Japan, the seeds were stored
at c. −18◦ C to avoid germination loss, and germination experiments
were carried out within 12 months of the maturation of the seeds.
Petri dish experiments
Replicates of 25 seeds were sown on three layers of ﬁlter paper(Toyo, No. 1) in 90-mm plastic Petri dishes. About 15 mL of deionised
water was added to each dish so that about half the volume of each seed
was immersed. The Petri dishes were covered with lids and held at
12 h 25◦ C/12 h 15◦ C in the dark in an incubator. Seeds were observed
daily through a magnifying glass with a scale and about two-thirds ofthe volume of water in each Petri dish was replaced daily.
Examination of germination of seeds submerged in water
Thirty-ﬁve seeds were placed in a glass bottle (130 mL), and
120 mL of deionised water was poured into the bottle (water depth:c. 60 mm); the 10–20% of seeds that ﬂoated were discarded. The
bottle was covered with a lid and held at 12 h 25◦ C/12 h 15◦ C in thedark in an incubator. After being submerged for 2, 3 or 5 days, seeds
were removed from the bottle, transferred to a Petri dish as describedabove, and seed germination and seedling emergence observed as
described above for another 6 days. Each treatment was replicatedfour times.

K. Tobe et al.

surviving seedlings in each pot was counted. A seedling was regarded
as having emerged when its height exceeded 3 mm, and a seedling was
regarded as having died when it fell over or most of the seedling turned
yellow or brown.
Seedling emergence from seeds buried at different depths
in different types of sand and irrigated under different regimes
Seeds were sown on the surface or at a depth of 2.5, 5.0 or
10 mm in ﬁne or coarse sand in the short pots. The pots were initiallyirrigated with deionised water of 16 mmP (x mmP denotes irrigationequivalent to x mm precipitation) and subsequently with water of
3 mmP at 1-day intervals ([16 + 1/1] treatment) for 14 days, or initiallyirrigated with water of 8 mmP and subsequently with water of 3 mmP
at 2-day ([8 + 1/2] treatment) or 4-day ([8 + 1/4] treatment) intervals
for 14 days. Each treatment was replicated ﬁve times. For pots inwhich seeds were sown on the sand surface and irrigated for 14 days,
seeds were transferred to Petri dishes described above and held in an
incubator (12 h 25◦ C/12 h 15◦ C in the dark), and seed germinationand seedling growth were observed daily as described above foranother 10 days.
Seedling emergence and survival when seeds were buried
at a depth of 10 mm in ﬁne sand and irrigated with different
amounts of water
To investigate the effect of the amount of irrigation on seedlingemergence and seedling survival, seeds were sown at a depth of
10 mm in ﬁne sand in the long pots and initially irrigated with deionised
water at 4, 6, 8, 12, 16, 20, 24 or 32 mmP and subsequently was
not irrigated at all for 20 days (4–16 mmP irrigation) or 40 days
(20–32 mmP irrigation). For treatments in which initial irrigation was
4–16 mmP, each pot was irrigated with 8-mmP on day 20 after the initialirrigation and subsequently with 3 mmP at 2-day intervals for another20 days to determine whether pots that did not produce emerging
seedlings contained viable seeds. Each treatment was replicatedseven times.
Statistical analysis
Tukey’s test was used for comparison of multiple means. Percentage
values were arcsine transformed before statistical analysis. Statisticaltests were conducted at P < 0.05.

Examination of seedling emergence from sandResults

Replicates of 16 seeds were sown on the surface or at different
depths (2.5, 5.0 and 10 mm) in sand-ﬁlled cylindrical plastic pots
(inner diameter: 80 mm, sand surface area: ca 50 cm2 ) either 50 mm(short pots) or 100 mm (long pots) tall. There was a circular drainage
opening (diameter: 12 mm) covered with cloth at the bottom of each pot.
The pots were ﬁlled to a depth of 45 mm (short pots) or 90 mm (long pots)with air-dried sand (ﬁne or coarse). Fine sand was collected from a beachin Japan and washed repeatedly to remove salt and mud. The particlesize distribution of the ﬁne sand (91% by weight was 63–250 µm) was
similar to that of sand dunes in China (Nanking Institute of Soil Science1983). Coarse sand (91% by weight was 250–600 µm) was collectedfrom a river bed in Japan, repeatedly washed to remove mud, and sieved
to remove small particles.
The pots were placed in an incubator and held at 12 h 25◦ C (light)/
12 h 15◦ C (dark). In the light period, the pots were illuminated withﬂuorescent lamps (photon ﬂux density at wavelengths of 400–700 nm
at the surface of the sand: 80–130 µmol m−2 s−1 ). Relative humidity inthe incubator was usually 40–70% during the 25◦ C (light) and 90–95%
during the 15◦ C (dark) periods. Pots were irrigated at the beginningof light periods by slowly and evenly dripping water on the sand witha pipette. The pots were observed daily and the number of emerging and

Seed germination and seedling growth in water andin Petri dishes
After submergence of seeds for 2, 3 or 5 days, radicles(2–7 mm long) emerged from 10–50% of the seeds andmany of the longer radicles appeared abnormal (coiled).
After seeds were transferred to Petri dishes, some emerging
radicles continued to elongate and some seeds germinated.
The proportions of seeds that had been submerged for
2, 3 and 5 days that generated seedlings longer than 20 mm
in the dishes were 48 ± 10%, 28 ± 5.4%, and 7 ± 2.2%
(mean ± s.e.; n = 4), respectively.
By contrast, 99 ± 0.2% (mean ± s.e.; n = 5) of seeds that
had not been submerged in water but were irrigated in Petridishes generated seedlings longer than 20 mm on Day 4 after
irrigation (Fig. 1). The length of these seedlings on Day 6
after irrigation was 82 ± 22 mm (mean ± s.d., n = 76), andmost of these seedlings appeared normal.

Irrigation effects on seedling emergence

Australian Journal of Botany

Surviving seedlings (%)

100

75

50

25

0
0

2

4

6

8

10

12

14

Day

Fig. 1. Changes over time in seedling emergence (%) from seeds
sown at 10 mm in coarse ( , 䊐) or ﬁne ( , 䊏) sand and irrigated with
[16 + 1/1] ( , ) or [8 + 1/2] (䊐, 䊏) treatments (refer to the captionof Table 1 for each treatment). The change over time in the percentage
of seeds that generated seedlings longer than 20 mm when seeds
were moistened in Petri dishes is also shown (· · · × · · ·). Each point
represents the mean of ﬁve replications; error bars indicate s.e. where
it is larger than the symbol.

◦•

◦

•

These results showed that contact of seeds with air was
required for normal seedling growth and that submergenceof seeds caused a gradual loss of germinability.
Seedling emergence from seeds buried at different depths
in ﬁne or coarse sand and irrigated under different regimes
Seedling emergence from sand depended on seed burial
depth, irrigation regime, and sand type (Fig. 1; Table 1).
For example, burial at 10 mm (Fig. 1) resulted in more rapid
seedling emergence and higher ﬁnal seedling emergence incoarse sand than in ﬁne sand treatments, and in [8 + 1/2]
than in [16 + 1/1] treatments. For the [16 + 1/1] treatment,
the seedling emergence percentage from ﬁne sand washighest at a seed burial depth of 2.5 mm and markedly
Table 1. Final seedling emergence percentages from seeds sownat different depths in ﬁne or coarse sand in pots and irrigated under
different regimes
Pots were initially irrigated with 16 mmP and subsequently with
3 mmP at 1-day intervals ([16 + 1/1]) for 14 days, or initially irrigatedwith 8 mmP and subsequently with 3 mmP at 2-day ([8 + 1/2]) or
4-day ([8 + 1/4]) intervals for 14 days. Data are the mean ofﬁve replications. Values with the same superscript letter are notsigniﬁcantly different from each other (P < 0.05; Tukey’s test)
Irrigation
0 mm[16 + 1/1]
[8 + 1/2][8 + 1/4]

0e
0e
not
examined

Sand type and seed burial depth
Fine sandCoarse sand
2.5 mm 5.0 mm 10 mm
10 mm
55bc
5e
1e

45c
66bc
37cd

7de
56bc
60bc

65bc
97a
84ab

531

decreased with increasing seed burial depth. Many of theseedlings that emerged from a depth of 2.5 mm in the[16 + 1/1] treatment trailed over the sand surface, whereas
in the other irrigation treatments many seedlings elongatedstraight upward at the sand surface. By comparison, for the[8 + 1/2] and [8 + 1/4] treatments, seedling emergence
percentage from ﬁne sand was very low for seeds buried at
2.5 mm and fairly high for greater burial depths (Table 1).
The ﬁnal percentage of seeds that produced seedlings
longer than 20 mm in Petri dishes (Fig. 1) was considerably
higher than the ﬁnal seedling emergence percentages fromsand (Table 1), except for seeds buried at 10 mm in coarse
sand and irrigated under the [8 + 1/2] treatment. Except
for 39% of seedlings that emerged from coarse sandirrigated at [8 + 1/4] that died by the end of the experiment,
all other emerging seedlings survived until the end of theexperiment. When seeds that were buried at 10 mm inﬁne sand and irrigated with [16 + 1/1] for 14 days wereexcavated from the sand, 81% of seeds were found to havegerminated (mean length of unemerged seedlings: 43 mm),but the radicles did not elongate downwards, and the seedlings
tended to elongate laterally without emerging from thesand surface.
When seeds were sown on the surface of ﬁne sandand irrigated under the [16 + 1/1] or [8 + 1/2] regimes,
no established seedlings were produced (Table 1). For the[16 + 1/1] treatment, although emergence of radicles(lengths: 1–10 mm) was found in 60–100% of seeds,
the radicles did not elongate further, and longer radicles
elongated laterally without penetrating into the sand. Whenseeds were transferred to Petri dishes after 14 days of[16 + 1/1] irrigation on the sand surface, the ﬁnal percentage
of seeds that generated seedlings longer than 20 mm was
66 ± 11.3% (mean ± s.e.; n = 5). For many seeds that had
generated fairly long radicles on the sand surface, the seedlinglength remained less than 20 mm in the Petri dishes, and theradicle tips were missing and/or the seedlings were coiled.
For the [8 + 1/2] treatment, radicle emergence was found in
c. 4% of seeds sown on the sand surface (radicle lengths:
1–2 mm). When seeds sown on the sand surface and irrigatedwith [8 + 1/2] were transferred to Petri dishes, the ﬁnal
percentage of seeds that generated seedlings longer than
20 mm in the dishes was 93 ± 2.7%, and all these seedlings
appeared normal.
Seedling emergence and seedling survival when seeds
were buried at a depth of 10 mm in ﬁne sandand irrigated with different amounts of water
Initial irrigation of 8–20 mmP resulted in high seedlingemergence percentages, but initial irrigation exceeding
20 mm tended to result in lower seedling emergence
percentages (Fig. 2; Table 2). The seedling emergence
percentage was very low or zero for the initial irrigation of
4 mmP or 6 mmP. Rewatering after the initial 4 mmP

532

Australian Journal of Botany

K. Tobe et al.

initial irrigation increased, emerging seedlings survived
for longer periods (Fig. 2; Table 2). Seedling emergence
was retarded with increasing amount of initial irrigation(Fig. 2; Table 2).

Surviving seedlings (%)

60

40

Discussion
The contrasting initial growth responses between submerged
seeds and seeds irrigated in Petri dishes indicated that
H. ammodendron requires contact with air for favourable
seedling growth. Poor germination of submerged seeds
has been reported for many species and has been attributed
to reduced oxygen availability (Morinaga 1926; Hegarty1978). Oxygen availability affects seed germination andseedling growth in many species (Heichel and Day 1972;
Crawford 1977, 1992; VanderZee and Kennedy 1981;
Al-Ani et al. 1985).
Emergence of seedlings of H. ammodendron from sanddepends on seed burial depth, irrigation regime, and sandparticle size, primarily because of the air : moisture ratio
in sand. Excessive irrigation reduced seedling emergencepresumably because the higher moisture content lowered
the air content in the sand, resulting in oxygen deﬁciency
for seeds and seedlings. Higher seedling emergence fromcoarse sand than from ﬁne sand was probably due to air
in the sand being purged by irrigation to a greater degree
in ﬁner sand. Nevertheless, ﬁne sand appeared to favour
survival of seedlings by retaining moisture because seedling
death in the [8 + 1/4] treatment occurred only in the coarse
sand treatment. Because the particle size of desert sand fromdunes in China is relatively small (Nanking Institute of Soil
Science 1983), these results suggest that only a small fractionof H. ammodendron seeds buried in sand develops into
established seedlings. A similar response of seed germination

20

0
0

5

10

15

20

25

30

35

40

Day

Fig. 2. Changes over time in seedling survival (%) from seeds buried
at 10 mm in ﬁne sand in pots and irrigated under different regimes. Pots
were irrigated initially with 4 mmP ( ), 8 mmP (䊐) or 16 mmP () andsubsequently not irrigated for 20 days (day 0–20), and on day 20, thepots were rewatered with 8 mmP and subsequently with 3 mmP at 2-day
intervals (days 20–40). : Pots were irrigated initially with 32 mmP
and subsequently not irrigated for 40 days. Each point represents themean of seven replications.

◦treatment caused seedlings to emerge from 58% ofseeds (Days 20–40), which was similar to the seedlingemergence percentage when seeds buried at 10 mm were
irrigated with [8 + 1/2] without pre-irrigation treatment(56%; Table 1). The seedling emergence percentage after
rewatering decreased markedly as the amount of initialirrigation increased and was zero for the initial 16 mmP
treatment (Table 2). For the initial 16 mmP treatment,
although seedlings did not newly emerge after the rewatering,
9% of seedlings that had fallen over on Day 20 recovered(Fig. 2); for other irrigation treatments, recovery of seedlings
was not observed after rewatering. As the amount ofTable 2. Effects of amount of irrigation on seedling emergence and seedling survival
Seeds were sown at a depth of 10 mm in ﬁne sand in pots, and the pots were initially irrigated with different
amounts of water and subsequently not irrigated at all for 20 days (4–16 mmP) or 40 days (20–32 mmP).
For treatments in which initial irrigation was 4–16 mmP, each pot was rewatered with 8-mmP on Day 20 after
the initial irrigation and subsequently with 3 mmP at 2-day intervals for another 20 days. Data are the meansof seven replications. In each column, the values with the same superscript letter are not signiﬁcantly
different from each other (P < 0.05; Tukey’s test). Dashes denote that the values were not calculated because
the ﬁnal seedling emergence percentage of one or more of replications was zero
Irrigation (mmP)

4
6
8
12
16
20
24
32

Number of days
after irrigation
when seedlingemerged initially

Emergence (%)

Number of days
after irrigation
when all seedlingsdied

New seedlingemergence after
rewatering
(%)

–
–
3.3a
4.4a
4.7b
5.4b
7.9b
–

0d
5cd
48a
36a
41a
36a
27ab
15bc

–
–
7.7a
13.1ab
19.3b
27.0b
34.3c
–

58a
15b
5bc
1c
0c
not examined
not examined
not examinedIrrigation effects on seedling emergence

was reported for the shrub Calligonum comosum L’Her. indeserts in Israel (Koller 1956); seed germinability of thisspecies was lost by washing the seeds with water, and becauseof the inhibitory effect of excessive water, its habitats are
conﬁned to areas covered with coarse sand and having low
rainfall (Koller 1956).
The very low seedling emergence from seeds buried
at 2.5 mm in ﬁne sand in the [8 + 1/2] and [8 + 1/4]
treatments may be attributed to moisture deﬁciency inshallower sand layers (Batanouny and Zieogler 1971;
Maun and Lapierre 1986) where moisture is rapidly lostby evaporation.
Another factor affecting the emergence of seedlingsof H. ammodendron from sand may be the obstruction of
seedling growth by mechanical resistance of moist sand.
Mechanical resistance of soil can impede shoot or root growthof seedlings (Gill and Miller 1956; Sedgley and Barley
1963; Barley and Greacen 1967; Taylor and Gardner 1963).
When sand contains water, sand particles coagulate and thesand becomes harder (Hornbaker et al. 1997) and exerts
stronger resistance to seedling elongation. In the [16 + 1/1]
treatment, seedling emergence from ﬁne sand was inhibitedat depths of 5.0 mm or more, primarily because seedlings
elongated laterally. Higher moisture content in deeper
sand in the more frequent irrigation treatment can cause
greater hardening of the deeper sand. This hardeningof deeper sand appeared to have inhibited downward
elongation of radicles and forced the seedlings to elongate
laterally. The higher seedling emergence percentages froma depth of 2.5 mm in the [16 + 1/1] treatment may be
because seeds were located closer to the sand surface, andthe seedlings, although elongating laterally, were better
able to emerge at the surface. Better seedling emergencefrom coarse sand in the [16 + 1/1] treatment may be
because moist coarse sand is less hard than moist ﬁne sand(Krumbein 1959).
Seeds sown on the sand surface did not give rise toestablished seedlings. This may be because moisturedeﬁciency at the surface did not allow seed germination or
seedling growth. In addition, radicles emerging at the sandsurface were not able to penetrate into the sand. A similar
response of radicles has been reported in other species(Maun and Riach 1981; Maun and Lapierre 1986; Tobe
et al. 2005). These results indicated that seed burial in sandis a requirement for the establishment of H. ammodendron
seedlings. For the short-lived seeds of H. ammodendron,
many seeds may lose viability before becoming buriedin sand.
Different amounts of irrigation produced different effects
on the seedling emergence percentages, the number of days
needed for seedlings to emerge after irrigation, percentagesof viable seeds after irrigation, and the period of survival of
emerging seedlings. These effects may have been because
different amounts of initial irrigation caused different

Australian Journal of Botany533

changes over time in the air : moisture ratio and hardnessof the sand. As the amount of irrigation is increased, themoisture content in the sand increases and persists for longer
periods (Tobe et al. 2005). Retardation and suppression of
seedling emergence with greater irrigation may have resulted
because oxygen deﬁciency (and perhaps sand hardening)caused by higher moisture content and longer persistenceof moisture in sand hindered seed germination and/or
seedling growth.
Increases in the period of survival of emerging seedlings
with increased amounts of irrigation may be because a larger
amount of irrigation moistened sand more deeply andmoisture persisting in deeper sand supported the survival ofseedlings for longer periods (Tobe et al. 2005). This indicatesthat after a light rainfall, successive rainfalls are needed
within shorter periods for the emerging seedlings to survive.
For H. ammodendron, the threshold amount of irrigationthat was needed to cause seedling emergence was small
compared to that for other species distributed in deserts (Went
1948; Tevis 1958; Ackerman 1979; Loria and Noy-Meir
1980; Gutterman and Evenari 1994; Tobe et al. 2005). Thismay be related to rapid germination after irrigation and seedgerminability at extremely low water potentials in this species(Tobe et al. 2000a). However, emerging seedlings did notsurvive for longer periods in moisture-deﬁcient conditions
compared to those of other species distributed in deserts(Tobe et al. 2005). Our results suggested that infrequent
supply of a fairly small amount of water causes germinationof H. ammodendron seeds, eliminates a considerable fractionof buried viable seeds from the seed bank and results inthe death of most emerging seedlings. Supplying a larger
amount of water is more likely to result in successful seedlingestablishment, although it results in seedling emergence fromonly a small fraction of the seeds.
In deserts in China, where winter temperatures fall below
0◦ C, seedlings of H. ammodendron are likely to emerge fromspring to autumn, and subsequently, ungerminated seeds lose
viability. In a typical habitat of H. ammodendron in China,
Fukang (44◦ 18 N, 87◦ 55 E; annual precipitation: 172 mm,
annual mean temperature: 6.1◦ C), monthly precipitationfrom April to October is highest in June (28 mm) and lowest
in August (11 mm) (means from 1958 to 1980), suggestingthat rainfall in this region is less frequent or the amount ofeach rainfall is less than the frequency or amount of irrigationneeded to support the survival of H. ammodendron seedlingsin our experiments. Thus, in such habitats, rainfall may be
more likely to cause the loss of viable seeds without resulting
in established seedlings. However, in Fukang and otherwestern parts of deserts of China, where H. ammodendronis distributed, some snowfall occurs in winter, and thissnow melts in the early spring, thereby supplying fairly
large amounts of water (Tobe et al. 2000b). For example,
in Fukang, precipitation from November to March is 36 mm(mean from 1958 to 1980), and usually falls as snow. In these534

Australian Journal of Botany

K. Tobe et al.

regions, H. ammodendron seeds, maturing in November, willremain ungerminated in the winter cold and be stimulated
to germinate by the water supplied by melting snow. Someof the seeds will give rise to established seedlings, andmost of buried viable seeds will be lost from the seedbank. After this season, seeds that had been located on
the sand surface may remain ungerminated and viable, but
for the short-lived seeds of this species, the opportunities
for these seeds to generate established seedlings may belimited. Mature plants of this species disperse a large
number of seeds every year, but a very small fraction of
the seeds are expected to give rise to established seedlingsin the ﬁeld.
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Manuscript received 13 December 2004, accepted 19 June 2005

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