Seed Science Research (2006) 16, 61 – 69

DOI: 10.1079/SSR2005230

Seed germination and seedling emergence of three Artemisia
species (Asteraceae) inhabiting desert sand dunes in China
Kazuo Tobe1*, Liping Zhang2 and Kenji Omasa3
1

Laboratory of Intellectual Fundamentals for Environmental Studies, National Institute for Environmental Studies,
16 – 2 Onogawa, Tsukuba, Ibaraki 305–8506, Japan; 2Cold and Arid Regions Environmental and Engineering
Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China; 3Graduate School of Agriculturaland Life Sciences, University of Tokyo, 1 – 1 – 1 Yayoi, Bunkyo, Tokyo 113–8657, Japan

Abstract
Artemisia ordosica, A. arenaria and A. sphaerocephala are semi-shrubs inhabiting desert sand dunes
in China and often used to rehabilitate desertified
areas. Improvement of dune rehabilitation successby sowing requires better understanding of theprocesses involved in the control of seed germination and seedling emergence in these species.
Thus, (1) effects of temperature, light and osmotica(polyethylene glycol-6000) on seed germination,and (2) effects of seed burial depth in sand andirrigation regime on seedling emergence, werestudied under controlled conditions. Seeds of thethree species required light for germination, and thelight fluence needed for germination was dependent
on temperature. Seedling emergence of the three
species was maximal (70–94%) for seeds sown at a
depth of 2.5 mm, and decreased with increasing
seed burial depth when the pots were initially andsubsequently treated with 16 mm and 3 mm irrigation at 1-d intervals. However, when the pots were
initially and subsequently treated with 8 mm and
3 mm irrigation at 2-d intervals, seedling emergence
was almost completely suppressed due to water
deficiency in sand. It is suggested that theprobability of seed germination and seedlingemergence of the three species in the field is very
limited, because the light requirement restricts seedgermination to shallow sand layers where water islost rapidly due to evaporation. Temperatureappeared to have secondary effects on seedgermination, by modifying the light sensitivity ofseeds.

*Correspondence
Fax: þ81 29 850 2587
E-mail: tobe@nies.go.jp

Keywords: Artemisia arenaria, Artemisia ordosica,
Artemisia sphaerocephala, irrigation, light, seed burial
depth, temperature

Introduction
Artemisia species (Asteraceae) are widely distributed in
the northern hemisphere. Some Artemisia species are
dominant in the deserts of Israel and North America,
and their seed germination characteristics have beenreported (Koller et al., 1964a, b; Friedman and Orshan,
1975; Young and Evans, 1975, 1989a, b; Meyer et al.,
1990; Huang and Gutterman, 1998). Fifty-one speciesof Artemisia (17 semi-shrubs and 34 herbs) are
reported to occur in the deserts of China (Lanzhou
Institute of Desert Research, 1992). Among them, thedeciduous semi-shrubs, A. ordosica Krasch., A. arenaria
DC. and A. sphaerocephala Krasch., inhabit sand dunes
and are often used to rehabilitate desertified dunes in
China. A. arenaria occurs in the central and western
Chinese deserts, while A. ordosica and A. sphaerocephalaoccur in the central and eastern deserts. A. sphaerocephala is found on mobile dunes, whereas A. ordosica
and A. arenaria are found on semi-stable or stable
dunes (Kobayashi et al., 1995; Hirobe et al., 2001; Qiu
et al., 2001a, b). For the rehabilitation of desertified
dunes in China, seeds (achenes) of these species areoften dispersed by aircraft. Improvement of dune
rehabilitation success by seed dispersal requires abetter understanding of the processes involved in thecontrol of seed germination and seedling emergencein these species.
Huang and Gutterman (1999, 2000) reported that
seeds of A. ordosica and A. sphaerocephala required lightfor germination and did not germinate when buried
deeply in sand. Seeds of both species have a

62

K. Tobe et al.

mucilaginous coat and accumulate a substantial
amount of water in the mucilage after watering.
Positive photoblastism and the presence of a
mucilaginous seed coat have been reported for otherspecies of Artemisia. In A. monosperma, a dominantshrub in sandy deserts of Israel, germination was
stimulated by very weak light (Koller et al., 1964b),
independently of wavelength (Koller et al., 1964a),thus suggesting that germination was induced by thevery low fluence response (VLFR) of phytochromes(Dixit and Amritphale, 1996; Casal et al., 1998).
In psammophytic species requiring light for
germination, seed germination is limited to theshallow sand layers where light penetrates (Woolley
and Stoller, 1978; Bliss and Smith, 1985; Tester andMorris, 1987; Mandoli et al., 1990). However, seedgermination in shallow sand layers may be constrained by additional critical factors, such as higher
temperature and lower water availability due to rapid
evaporation after rainfall events (Mott, 1972, 1974;
Tobe et al., 2005a), thus hindering water uptake by
seeds in this layer. Water availability is an important
limiting factor for seed germination in desert
environments (Tevis, 1958; Ackerman, 1979; Loria
and Noy-Meir, 1979/1980; Gutterman and Evenari,1994). Thus, restriction of seed germination to theshallow sand layers may considerably reduce seedlingestablishment of the Artemisia species used for dune
rehabilitation. Although seedling emergence in
A. ordosica and A. sphaerocephala was examined undersufficiently irrigated conditions (Huang and Gutterman, 1999, 2000), their response to limited water
availability is not known.
In this study, we investigated seed germinationand seedling emergence of A. ordosica, A. arenaria andA. sphaerocephala that are used for dune rehabilitation,
particularly with regard to water availability in sand.
We examined the effects of temperature, light andpolyethylene glycol (PEG)-6000 on seed germinationand the effects of seed burial depth in sand andirrigation regime on seedling emergence.

the deserts in China, seeds of these Artemisia species
ripen in October. In these regions, winter temperatures
fall below 08C, inhibiting seed germination in winter.
In the middle and eastern parts of the deserts in China,
which are the main habitats of these species,
precipitation predominates in summer due to acontinental monsoon (Fullen and Mitchell, 1994). In
Shapotou, where A. ordosica and A. sphaerocephalaoccur, 87% of the annual precipitation fell between
April and September and 55% in July and August(1990–1995). In Shapotou, daily precipitation wasusually less than 8 mm between October and early
June, but often exceeded 24 mm between late June and
September; in 1996, the number of days per month inwhich daily precipitation exceeded 1 mm was 1, 2, 5, 7
and 5 d in April, May, June, July and August,respectively. In Shapotou, in 1996, the means of thedaily lowest and highest temperatures in April were
4.2 8C and 17.4 8C, respectively, and both the daily
lowest and highest mean temperatures were highest
in July (18.0 8C and 29.0 8C, respectively).
Except for seeds used for the dormancy test, thecollected seeds of A. ordosica and A. arenaria were
initially stored dry at room temperature (c. 23 8C) for
12 months (A. ordosica) or 6 months (A. arenaria) tobreak seed dormancy, and thereafter, stored dry in arefrigerator (c. 0 8C) until they were used forexperiments. A. sphaerocephala seeds were stored dryin a refrigerator (c. 0 8C) until they were used forexperiments. Seed weights of A. ordosica, A. arenaria
and A. sphaerocephala were 0.27 ^ 0.10 mg,
0.76 ^ 0.11 mg and 0.70 ^ 0.12 mg (mean ^ SD,
n ¼ 20), respectively. Experiments were carried out
from January 2000 to September 2002, except forexperiments with A. ordosica seeds collected in 2000,
which were carried out in July and August 2005.

Materials and methods

Replicates of 25 seeds were sown on three layers offilter paper (Toyo, No. 1) in a 90-mm glass or plastic
Petri dish with about 10 ml of deionized water. The
Petri dishes were covered with lids and maintained in
an incubator at a constant temperature (10–30 8C) or adiurnally alternating temperature regime (12-h thermoperiods of 10 8C/20 8C, 15 8C/25 8C or 20 8C/30 8C)
in interrupted dark or 12-h light/12-h dark. In theinterrupted dark treatment, seeds were maintained in
darkness, except for 1–2 min daily exposure to dim
light [photon flux density (PFD) c. 2 mmol m22 s21 atwavelengths 400–700 nm], to monitor germination. In
light/dark treatment, seeds were illuminated withfluorescent lamps (PFD 80–90 mmol m22 s21) during

Materials
Seeds of A. ordosica were collected in December 1997
and October 2000 from a sand dune in Shapotou(37 8260 N, 104 8570 E; annual precipitation, 188 mm;
annual mean temperature, 10.5 8C); A. arenaria seeds
in October 2000 from a field botanical garden in
Minqin (38 8340 N, 102 8580 E; annual precipitation,
120 mm; annual mean temperature, 7.8 8C); and A.
sphaerocephala seeds in February 2000 from a sanddune in Dengkuo (40 8230 N, 106 8560 E; annual precipitation, 149 mm; annual mean temperature, 7.4 8C). In

Methods
Experiment 1: Effects of temperature on seedgermination in interrupted dark and light/dark
photoperiods

Germination and establishment of Artemisia
the 12-h photoperiods. In the treatments in whichphotoperiods were combined with alternating temperature regimes, seeds were exposed to the lower
temperatures during the 12-h dark period. During theperiod of exposure to light, the temperature in the Petridishes was c. 2 8C higher than that in the incubator. In
all the treatments, germination was monitored daily,and seeds with radicles longer than 5 mm wereregarded as germinated and discarded; about twothirds of the volume of the fluid in each Petri dish was
replaced daily. Final germination percentage (GF), thenumber of days until seed germination was initiallyobserved (Tinit) and the number of days until 0.5 £GF% of seeds germinated (T1/2) were determined after
14 d of incubation.
Experiment 2: Effects of water potential on seedgermination in interrupted dark and light/dark
photoperiods
The effects of water potential on seed germination
were examined by incubating seeds, as described inExperiment 1, at 20 C either in interrupted dark or
12-h light/12-h dark with deionized water or PEG6000 solutions [water potential (CW) 0 to 2 1.2 MPa,
determined using an isopiestic psychrometer at 20 8C;
Boyer and Knipling, 1965]. To maintain the temperature of the seeds at 20 8 C, the temperature in the
incubator was set at 18 8C during the 12-h photoperiods. GF, T1/2 and Tinit were determined after 20 dof incubation.
Experiment 3: Seed germination in complete dark
and effects of low-fluence light on seed germination
To examine seed germination in complete darkness,seeds were incubated in the dark, as described inExperiment 1, at different temperature regimes (20 8C,
12-h 10 8C/12-h 20 8C, 12-h 15 8C/12-h 25 8C or 12-h
20 8C/12-h 30 8C) without daily observation. Additionally, to examine the sensitivity of seed germination to
low-fluence light exposure, the effects of one-time
illumination with dim light (PFD c. 2.5 mmol m22 s21)
for 5 min, 5 d after irrigation, on GF were examined. GF
was determined after 10 d of incubation.
Experiment 4: Effects of seed burial depth andirrigation regimes on seedling emergence
Replicates of 16 seeds were sown on the surface or at a
depth of 2.5, 5.0, 10 or 15 mm in dry sand in drained
cylindrical plastic pots (inner diameter, 80 mm; height,
50 or 100 mm; sand depth, 45 or 90 mm). Sand used inthis experiment was described in Tobe et al. (2005a),and is similar in particle-size distribution to that of thesand in the desert sand dunes in China. The pots wereplaced in an incubator and maintained at 12-h 25C63(light)/12-h 15C (dark), 40 – 70%/90 – 95% relative
humidity (RH), and PFD of 80 –130 mmol m22 s21 at
the sand level from fluorescent lamps during thephotoperiod. Six irrigation regimes were applied:
initial irrigation with water of x mmP (x ¼ 8 or 16;
x mmP denotes irrigation equivalent to x mm precipitation) and subsequent irrigation with water of 3 mmP
at 1-d intervals ([8 þ 1/1] and [16 þ 1/1] treatments)
or 2-d intervals ([8 þ 1/2] and [16 þ 1/2] treatments),
and initial irrigation with water of x mmP (x ¼ 16 or 24)
and no subsequent irrigation ([16 þ 0] and [24 þ 0]
treatments). The pots were examined daily, and thenumber of emerging (seedling height . 3 mm) andsurviving seedlings was counted. Seeds that germinated but failed to emerge were retrieved in the[16 þ 1/1] treatment by sieving the sand. At seedburial depths of 10 mm and 15 mm, where very low
emergence was observed, viability of the ungerminated seeds was examined by spreading the sand ofeach pot in a flat plastic container (mean sand depth c.
2 mm), further irrigating for 16 d and monitoring
germination under interrupted dark (PFD c.
5 mmol m22 s21) daily for 2– 5 min. For each irrigation
regime, sand water content at different depth ranges(0 –5 mm, 5–10 mm and 10 –20 mm) in the pots wasdetermined as described in Tobe et al. (2005a), 1, 2, 3, 4, 5
or 10 d after the irrigation was begun.
Statistical analysis
Student’s t-test was used to test statisticallythe difference between two means. Analysis ofvariance (ANOVA), followed by Tukey’s test, wasused to compare more than three means. Percentage
values were arcsine transformed prior to statisticalanalysis.

Results
Seed dormancy
In A. ordosica, at 0, 2.5 and 8.7 months after storage at
238 C, GF (20 8C, interrupted darkness) was 24 ^ 5%,37 ^ 5% and 87 ^ 4% (mean ^ SE), respectively,
while GF of the seeds stored at c. 0 8C for 8.7 months
remained low (19 ^ 3%). In A. arenaria, 13 d after seedcollection, GF was 20 ^ 2%, as compared to 87 ^ 3%
and 61 ^ 3% for seeds stored for 6 months at 23 8C and
0 8C, respectively. Thus, in A. ordosica and A. arenaria, alarge proportion of seeds possess primary dormancy,
which is gradually relaxed during storage at 23 8C for
several months. In contrast, it appeared that A.
sphaerocephala either lacked or possessed a very
short period of primary dormancy, sincegermination was high (GF ¼ 92 ^ 3%) 2 months after
seed collection.

K. Tobe et al.

64

Table 1. The effects of temperature and light on the final germination percentages (GF), the number of days until germination
was initially observed (Tinit) and the number of days until 0.5 £ GF% (T1/2), for seeds of three Artemisia species. D, interrupted
dark; L, light/dark. Dashes denote that the values were not calculated because GF of one or more replications was zero. Values
are the means of four replications. For each parameter and species, the values having the same letters are not significantly
different (P , 0.05; Tukey’s test)
Tinit (d)GF (%)
Temperature
A. ordosica
108C
158C
208C
258C
308C
108C/208C
158C/258C
208C/308C
A. arenaria
108C
158C
208C
258C
308C
108C/208C
158C/258C
208C/308C
A. sphaerocephala
108C
158C
208C
258C
308C
108C/208C
158C/258C
208C/308C

T1/2 (d)

D

L

D

L

D

L

43 c
94 ab
94 ab
81 ab
20 cd
88 ab
94 ab
86 ab

8d
90 ab
90 ab
77 b
26 cd
95 ab
97 a
84 ab

6.7 c
3.7 ab2.2 a
2.0 a
2.7 ab
3.5 ab
2.5 ab
2.5 ab

11.2 d
3.7 ab
2.5 ab
2.0 a
3.5 ab4.2 b
3.2 ab
3.0 ab

7.7 e
3.8 abc
2.8 a
2.8 a
3.8 abc
4.4 abc
2.7 a
2.9 a

12.2 f
5.4 bcd
3.7 abc
3.4 ab
6.7 de5.7 cde
4.1 abc
4.0 abc

63 bc
90 a
89 a
47 c
1f
90 a
85 a
81 ab

22 de
84 ab
80 ab
43 cd
8 ef
82 ab
88 a
82 ab

7.0 d
3.5 abc
2.5 ab2.0 a–
4.0 abc
3.0 abc
3.0 abc

9.5 e
4.5 bc
3.2 abc
3.2 abc
4.5 bc
5.2 cd
3.5 abc
2.7 ab

7.5 ef
3.9 abc
2.6 a
2.8 a
–
4.1 abc
2.9 a
3.3 ab

10.6 g
5.9 bcdef
4.3 abcd
6.7 cdef
5.7 bcdef
7.9 fg
5.0 abcde
7.2 def

10 def
79 ab
96 a
85 ab
6 ef
55 bc
86 ab
93 a

0f
40 cde85 ab
45 cd
14 def35 cde
86 ab
94 a

8.0 c
3.7 ab2.2 a
2.0 a
4.0 abc
4.2 abc
3.0 ab
2.5 a–
7.0 bc
3.7 ab
2.7 a
–
8.0 c
4.0 abc
3.0 ab

8.2 cde
4.3 ab
3.2 a
3.1 a
3.7 a
7.3 bcd
3.6 a
3.1 a

–
9.0 de5.6 abc
5.0 ab
–10.8 e7.2 bcd
4.9 ab

Effects of temperature on seed germination ininterrupted dark and light/dark photoperiods

Effects of water potential on seed germination ininterrupted dark and light/dark

In both the interrupted dark and light/dark treatments, GF in the three species was significantly lower
at 10 8 C and 30 8C than at the other temperature
regimes (Table 1). At 10 8C and a few othertemperature regimes, GF was lower and germination
was retarded more in light/dark than in interrupted
dark. As compared to A. ordosica, A. arenaria and A.
sphaerocephala showed somewhat lower GF at higher
and lower temperatures, respectively. GF was considerably higher at 10 8C/20 8C and 20 8C/30 8C than at
10 8C and 30 8C, indicating that the inhibitory effects ofhigh/low temperature during the day/night on seedgermination can be mitigated by lower/higher
temperature during the night/day. On comparing
the results with temperature data in the field, we
found that seeds of these three species are germinable,
at least in interrupted dark, at most temperatures
recorded between mid-spring and mid-autumn inmany desert regions in China (data not shown).

A decrease in CW decreased GF and retarded
seed germination in both the interrupted dark andlight/dark treatments in the three species (Table 2). GF
at 2 1.2 MPa was zero or almost zero, except in theinterrupted dark treatment of A. ordosica (13%). As
compared to interrupted dark, the light/dark treatment resulted in the reduction of GF, particularly at
lower CW; and the inhibitory effect was stronger andover a wider CW range for A. sphaerocephala.
Seed germination in complete dark and effects of
low-fluence light on seed germination under
different temperature regimes
For some temperature regimes, GF in complete
darkness (Table 3) was considerably lower than thatin interrupted dark (Table 1), indicating that the highGF values in interrupted dark resulted from theGermination and establishment of Artemisia

65

Table 2. The effects of water potential and light on final germination percentages (GF), the number of days until seed germination
was initially observed (Tinit) and the number of days until 0.5 £ GF% (T1/2) at 208C for seeds of three Artemisia species. D,interrupted dark; L, light/dark. Dashes denote that the values were not calculated because GF of one or more replications was
zero. Values are the means of four replications. For each parameter and species, the values having the same letters are notsignificantly different (P , 0.05; Tukey’s test)
Tinit (d)GF (%)
Water potential (MPa)A. ordosica
0
2 0.3
2 0.6
2 0.9
2 1.2
A. arenaria
0
2 0.3
2 0.6
2 0.9
2 1.2
A. sphaerocephala
0
2 0.3
2 0.6
2 0.9
2 1.2

D

L

D

L

D

L

92 a
91 ab
78 b
45 c
13 d

90 ab
89 ab
81 bc
18 e
2f

2.0 a
2.5 a
3.0 a
4.5 a
12.2 b

3.0 a
3.0 a
5.5 a
–
–

2.7 a
2.9 a
4.6 ab
7.7 bc14.9 d

3.5 a
4.8 ab
9.7 c
–
–

84 a
83 a
70 a
23 b
0c

82 a
74 a
60 a
2c
0c

2.0 a
3.0 a
4.0 ab
8.2 c
–

3.2 a
3.5 a
8.0 bc
–
–

2.5 a
3.0 a
5.6 ab
11.2 c–

4.8 a
5.5 ab
9.4 bc
–
–

94 a
89 ab
70 bc
32 de
3f

85 ab
52 cd
14 ef
2f
0f

2.7 a
3.0 a
4.0 ab
6.7 c–

4.2 ab5.2 bc
–
–
–

3.0 a
4.1 a
5.7 ab
9.0 bc–

8.3 bc9.3 c–––stimulation of seed germination by the dim light used
for daily observation. GF in complete darkness
differed among species and among temperature
regimes. Generally, GF in complete darkness was
greater in the order of 20 8C, 15 8C/25 8C, 10 8C/20 8C
and 20 8C/30 8C treatments.
One-time illumination with low-fluence light
resulted in a significant increase in GF in 20 8C
and 15 8C/25 8C treatments in all the three species(Table 3), but was generally insufficient forincreasing GF to the corresponding values observedin the interrupted dark treatment (Table 1). In the
Table 3. Final percent germination (GF) of Artemisia seeds
that were maintained under different temperature regimes,
illuminated with dim light (þ ) (PFD 2.5 mmol m22 s21) for
5 min 5 d after the onset of imbibition, or in complete
darkness ( – ). Values are the means of four replications. In
each column, the values having the same letters are notsignificantly different (P , 0.05; Tukey’s test)
Temperature Light A. ordosica A. arenaria A. sphaerocephala
108C/208C
158C/258C
208C/308C
208C

–
þ
–
þ
–
þ
–
þ

19 bcd
38 b
27 bc
73 a
5d
11 cd
30 bc
84 a

T1/2 (d)

7 cd
19 bc
4d
31 b
1d
0d
21 bc
68 a

1b
8b
1b
35 a
1b
8b
4b
39 a

10 8C/20 8C and 20 8C/30 8C treatments, althoughmean GF was increased by the low-fluence light inmost cases, none of the differences were significant(P . 0.05). In the one-time illumination treatment,
GF was significantly higher only at 20 8C and
15 8C/25 8C.

Seedling emergence from seeds sown at different
depths in sand and irrigated under different
regimes
In all the irrigation regimes, sand water content
increased with increasing sand depth (data notshown). For all the depth ranges, both an increase in
the amount of initial irrigation and an increase in thefrequency of irrigation resulted in persistence of waterin sand for longer periods.
When seeds in pots were irrigated under the[16 þ 1/1] regime (0 –16 d in Fig. 1), final percentage
seedling emergence (EF) in the three species was thehighest for seeds buried at 2.5 mm, followed byseeds sown on the sand surface. EF from 10 mm and
15 mm was almost zero for A. arenaria and A.
sphaerocephala, as compared to 31% and 16% for
A. ordosica. When the seeds were dug out from thesand on day 16, the percentages of seeds thatgerminated, but did not emerge, were very small(0 –4%), except for A. ordosica seeds that were buried
at 15 mm (18%). The percentage germination of

K. Tobe et al.

66(a) 100

(a)

75

75

50

50

25

25

0
0

4

8

12

16

20

24

28

0

32

(b) 100
(b)

75

0

4

8

12

16

20

24

0

4

8

12

16

20

24

0

4

8

12

16

20

24

100
75

50
25
0
0

4

8

12

16

20

24

28

32

Percentage

Percentage

100(c) 100
(c)

75

50
25
0
100
75

50
50

25

25

0
0

4

8

12

16
Day

20

24

28

32

0
Day

Figure 1. Time course of percent seedling emergence orpercentage germination of A. ordosica (a), A. arenaria (b) and A.
sphaerocephala (c). Seeds were sown on sand surface ( £ ) or
buried at 2.5 mm (V), 5.0 mm (O), 10 mm (B) or 15 mm (⁄) insand in pots (height 50 mm) placed at 258C (12 h, light)/158C(12 h, dark). The pots were irrigated initially with 16 mmP and
subsequently with 3 mmP at 1-d intervals ([16 þ 1/1]
treatment; 0 –16 d). Seeds buried at 10 mm or 15 mm weremoved to shallow depths in containers on day 16, andpercentage germination was examined for another 16 d (16–32 d) (initial seed burial depth: A, 10 mm; W, 15 mm). Eachvalue represents the mean of five replications; error bars
indicating SE are shown only for some representative values.

A. ordosica seeds buried at 10 or 15 mm was similar
to GF of the seeds maintained in complete darkness
at the same temperature regime (15 8C/25 8C in
Table 3). When the sand with non-germinated seeds
buried at 10 mm or 15 mm in the [16 þ 1/1]
treatment was spread into a thin layer andilluminated with low-fluence light, most of theseeds germinated within 16 d (16–32 d in Fig. 1).
In the [8 þ 1/2] treatment, seedling emergence wasalmost completely suppressed for the three species at
all seed burial depths, except A. ordosica seeds at
5.0 mm (0 –14 d in Fig. 2; EF ¼ 24%). When these pots
were subsequently treated with [8 þ 1/1] (14 –24 d in
Fig. 2), higher percentages of seedlings emerged at allseed burial depths in the three species. EF was
significantly lower (P , 0.001) in the [8 þ 1/1] than in
the [16 þ 1/1] treatment (Fig. 1) at burial depths of 0
and 2.5 mm, whereas at a seed burial depth of 5.0 mm,

Figure 2. Time course of percent seedling emergence of A.
ordosica (a), A. arenaria (b) and A. sphaerocephala (c) when seeds
were sown on sand surface ( £ ) or at a depth of 2.5 mm (V) or
5.0 mm (O) in sand in pots (height 50 mm) placed at 258C (12 h,
light)/158C (12 h, dark). The pots were irrigated initially with
8 mmP and subsequently with 3 mmP at 2-d intervals([8 þ 1/2] treatment; 0– 13 d), and thereafter, the pots were
irrigated initially with 8 mmP and subsequently with 3 mmP
at 1-d intervals ([8 þ 1/1] treatment; 14– 24 d). Each value
represents the mean of five replications; error bars indicating
SE are shown only for some representative values.

EF was significantly higher (P , 0.05) in the [8 þ 1/1],
followed by [8 þ 1/2], than in the [16 þ 1/1]
treatment, which is presumably because the moist
seeds received light for a longer period (24 d rather
than 16 d). After the [8 þ 1/1] treatment, when theungerminated seeds sown on the sand surface were
irrigated in Petri dishes, they germinated rapidly and
GF was 83% (A. ordosica), 81% (A. arenaria) and 99%(A. sphaerocephala).
The effects of different irrigation regimes on
seedling emergence were examined with A. ordosica
seeds collected in 2000 (Table 4). GF at 15 8C/25 8C incomplete dark was lower in these seeds (9 ^ 4%;mean ^ SE, n ¼ 4) than in A. ordosica seeds collected
in 1997 and used in the previous experiments(27 ^ 1%; Table 3). In all the irrigation regimes,
mean EF was the highest at 2.5 mm depth (Table 4).
While there were not significant differences in EF
between the [16 þ 1/1] and the [8 þ 1/1] treatments at

Germination and establishment of Artemisia

67

Table 4. The effects of irrigation regime on the final percent seedling emergence (EF; values
20 d after the irrigation was begun) for A. ordosica seeds (collected in 2000) buried in sandin pots (height 100 mm) placed at 258C (12 h, light)/158C (12 h, dark). Dashes denote notexamined. Values are the means of five replications. The values having the same letters are
not significantly different (P , 0.05; Tukey’s test)
EF (%)
Seed depth (mm)
0
2.5
5.0
10.0

v

[16 þ 1/1]

[8 þ 1/1]

91 a
96 a
55 bc
7 ef

75 ab
94 a
72 ab
–

w

[16 þ 1/2]x[24 þ 0]y[16 þ 0]z

21 cde54 bc
39 bcde–15 def44 bcd
29 cde0f

0f
24 cde0f–

V

Initial irrigation with water equivalent to 16 mm precipitation, with subsequentirrigation equivalent to 3 mm precipitation at 1 d intervals.
W
Initial irrigation with water equivalent to 8 mm precipitation, with subsequent irrigationequivalent to 3 mm precipitation at 1 d intervals.
X
Initial irrigation with water equivalent to 16 mm precipitation, with subsequentirrigation equivalent to 3 mm precipitation at 2 d intervals.
Y
Initial irrigation with water equivalent to 24 mm precipitation, with no subsequentirrigation.
Z
Initial irrigation with water equivalent to 16 mm precipitation, with no subsequentirrigation.

either 0 or 2.5 mm seed depths, EF was significantly
lower in the [16 þ 1/2] than in the [16 þ 1/1]
treatment at the depths of 0 and 2.5 mm. EF values in
one-time irrigation treatments ([16 þ 0] and [24 þ 0])
were generally lower than those in the other threetreatments. In the [16 þ 0] treatment, seedlings began
to die 16 d after irrigation and only 39% of seedlings
survived 20 d after irrigation; in the other four
irrigation regimes, all the seedlings survived during
the 20 d of the experimental period.

Discussion
Seed burial depth and the frequency/amount ofirrigation were important determinants of seedgermination in the three Artemisia species. The lightrequirement for seed germination in these species
limited their germination to shallow sand layers,
where water is rapidly lost due to evaporation.
Nevertheless, water potentials preventing seed germination in these species (c. 2 1.2 MPa) were similar
to, or rather higher than, the water potentials thatprevent germination of non-photoblastic seeds ofother species inhabiting deserts (Tobe et al., 2005a, b)
or more mesic habitats (Evans and Etherington, 1990).
When the seeds were irrigated in/on sand,[8 þ 1/2] irrigation was insufficient for appreciableseedling emergence in the three Artemisia species(Fig. 2), while for several other species inhabiting
desert dunes in China and producing non-photoblastic seeds, [8 þ 1/2] irrigation was sufficient toyield high percentages of seedling emergence fromseeds buried at 10 mm depth (Tobe et al., 2005a, b;

unpublished results). Additionally, while one-time
irrigation of 8–16 mmP was sufficient for yielding
high percentages of seedling emergence in thosespecies with non-photoblastic seeds (Tobe et al., 2005a,b; unpublished results), 24 mmP irrigation did notyield a high percentage of seedling emergence in
A. ordisica (Table 4). These results suggest that theopportunity for seed germination of the three
Artemisia species in the field is more limited,
compared to other species growing in the same
habitats and producing non-photoblastic seeds.
Precipitation in the field (see Materials andmethods) is considerably less frequent than theirrigation in our experiments. It is expected that, in
Shapotou and many other desert regions in China,
seed germination of the three Artemisia species isalmost completely suppressed from mid-autumn to
mid-spring, when rainfall events are usually less than
8 mm and occur at longer intervals. Seed germinationof these species is expected only in the summer rainyseason, when rainfall events often exceed 24 mm andoccur at a higher frequency. Some proportion of seeds
buried at relatively shallow depths will germinate inthis season, but seeds buried deeply or located near
the surface will remain ungerminated, but viable, andwill act as a seed reservoir for the future years.
However, the longevity of A. ordosica seeds was rather
short (, 6.7 years) when they were stored dry at c.
23 8C (unpublished data). Although seed longevity inlaboratory conditions cannot be extended to field
conditions, Artemisia seeds may not persist for very
long in seed banks in the field. A substantial
proportion of seeds may die before they have an
opportunity to germinate.

68

K. Tobe et al.

It should be stressed that the light intensity on sandin our experiments was 10–20 times lower than insunny field conditions. In sunny places where light
penetrates deeper into the sand (Huang and Gutterman, 1998), seed germination will be enabled indeeper sand layers where the water content is higher.
On the other hand, direct sunlight will cause atemperature rise near the sand surface, and evaporation will be enhanced to a greater extent, compared toour experimental conditions. Thus, in sunny places in
the field, seedling emergence may be disfavoured
more at shallower depths and favoured more in
deeper sand than expected from our study. In
addition, as was suggested by higher seedlingemergence percentages at 5 mm depth in the½8 þ 1=1, followed by [8 þ 1/2], than in the½16 þ 1=1 treatment (Figs 1, 2), if imbibed seeds
buried at relatively deep sand levels receive very weak
light for an extended period, they may be enabled togerminate at deeper sand levels than observed in our
experiments.
In the Negev Desert, Huang and Gutterman (1998)
found that the highest percentage of A. monosperma
seedlings emerged from seeds buried at 8–10 mm, andthat emergence from depths shallower than 4 mm anddeeper than 12 mm was very limited. Since lightsensitivity of the seeds of the three Artemisia species
examined in this study (Table 3) was considerably
lower than that of A. monosperma seeds [for which
irradiation with 0.1 lux (< 0.002 mmol m22 s21) of lightfor 4 min was sufficient to saturate germination(Koller et al., 1964b)], seed germination of these three
Artemisia species would be limited to a shallower sanddepth range where water content is lower. Hence, theopportunity for seedling establishment would be
more limited for the three Artemisia species studied
here, compared to A. monosperma. For seeds of A.
sphaerocephala, higher photoinhibition and lower lightsensitivity than the other two species may limit its
germination to a narrower depth range in sand. On theother hand, for A. ordosica and A. arenaria, primaryseed dormancy would prevent seed germination insome proportion of the seeds in the initial year after
maturation.
At optimal light conditions for germination(interrupted dark), seeds of the three Artemisia species
germinated at a wide range of temperature conditions,overlapping those occurring in the field between midspring and mid-autumn, during which a highproportion of annual precipitation occurs. However,under non-optimal light conditions (complete dark
and one-time illumination with low-fluence light;
Table 3), seed germination in these three species
showed stronger dependence on temperature. They
required lower-fluence light for germination, and ahigher proportion of seeds germinated without lightin 15 8C/25 8C than in 10 8C/20 8C and in 20 8C/30 8C(Table 3). The light sensitivity of seeds would have a
crucial effect on seedling emergence because higher
sensitivity to light would enable seed germination atsand depths where the water content is higher. The
temperature conditions in the summer rainy season
will correspond to the 15 8C/25 8C and 20 8C/30 8C
regimes in our experiments. Since seed germination inlimiting light conditions considerably differed
between these two temperature regimes (Table 3),
the temperature after precipitation can affect seedlingemergence of these species. In the field, sandtemperatures near the surface in the daytime can beconsiderably higher than air temperatures (Mott, 1972;
Zhang and Maun, 1990); however, when the sand near
the surface is moist, the only condition in which seeds
germinate, evaporative cooling will prevent an
extreme rise in sand temperature.
Our study suggested that the opportunity for seedgermination of the three Artemisia species in the fieldis limited because the light requirement for germination restricts their germination to dry, shallow sanddepths. Nevertheless, our experimental study underlaboratory conditions did not always simulate theenvironmental conditions of the species’ habitats. In
particular, light intensity, which depends on locations(sun or shade) and weather (sunny or cloudy), will
influence evaporation rate from sand and sandtemperature, and thus will affect the features ofgermination in these species. Field studies would beneeded for further understanding of the germination
behaviour of these species on dunes.

Acknowledgements
We thank Mr Yongguang Han and Dr Qiushi Wei forproviding the seeds of A. sphaerocephala and A.
arenaria, respectively.
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Received 31 January 2005
accepted after revision 8 November 2005
q CAB International 2006