Effect of Water Stress on Leaf Photosynthesis Chlorophyll Content and Growth of Orienyal Lily Zhang et al

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ISSN 1021�4437, Russian Journal of Plant Physiology, 2011, Vol. 58, No. 5, pp. 844–850. © Pleiades Publishing, Ltd., 2011.
844
1 INTRODUCTION
Photosynthesis is a core function of a plant, which
captures light energy to produce both chemical energy
and reducing equivalents via photochemical processes
[1]. Plants are exposed to a wide variety of abiotic
stresses, including excessive light, extreme tempera�
tures, water stress, and atmospheric pollutants, which
can directly or indirectly affect photosynthetic func�
tion. Water stress is one of the most important limita�
tions to photosynthesis and, therefore, to plant pro�
ductivity and plant growth [2]. For most plants, water
deficit leads to stomatal closure and reduced photo�
1 This text was submitted by the authors in English.
synthesis. Furthermore, prolonged drought can limit
plant growth and biomass production, alter the alloca�
tion pattern of biomass, and even cause plant death
[3]. Under water stress, biomass production of Populus
cathayana and P. przewalskii, as well as shoot height,
total biomass, total number of leaves, and total leaf
area, signicantly decreased [4]. Li et al. [3] reported
that soil drought could decrease of Sophora davidii
seedling leaf area, then limited photosynthesis, and
further decreased growth and productivity. Drought
stress decreased the net photosynthetic rate (Pn), tran�
spiration rate (E), stomatal conductance (gs) of
P. przewalski, thereby reducing plant growth and pro�
ductivity [5]. Water stress also causes a series of physi�
ological, biochemical, and morphological responses
in plants [6]. In S. davidii, Wu et al. [7] reported that
water stress led to a decrease in seedling leaf area (LA),
photosynthetic pigment content, reduced photosyn�
thetic efficiency, and enhanced photodamage to PSII
in the light. Zhang et al. [8] found that water defi�
ciency decreased the chlorophyll content and photo�
RESEARCH 
PAPERS
Effect of Water Stress on Leaf Photosynthesis, Chlorophyll Content, 
and Growth of Oriental Lily1 
Y. J. Zhanga, Z. K. Xiea, Y. J. Wanga, P. X. Sua, L. P. Ana, and H. Gaob
aCold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 
Lanzhou 730000, China;
e�mail: wxhcas@lzb.ac.cn
bCollege of Bowen, Jiaotong University, Lanzhou 730101, China
Received September 20, 2010
Abstract—The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to
increasing water stress were analyzed based on the net photosynthetic rate (Pn), stomatal conductance (gs),
intercellular CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE), and stomatal limi�
tation (Ls) in the Horqin Sandy Land of western China. A photosynthesis�PAR response curve was con�
structed to obtain light�compensation and light�saturation points (LCP and LSP), the maximum photosyn�
thetic rates (Pmax) and dark respiration rates (RD). The growth of lilies in the pots was analyzed after anthesis.
Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied.
The results indicated that drought stress not only significantly decreased Pn, E, gs, photosynthetic pigment
content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered
the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (Pn)�PAR response curve.
Drought stress increased LCP and RD and decreased LSP and Pmax. There were both stomatal and nonsto�
matal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal
limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and
affected the diurnal pattern of gas exchange and Pn�PAR response curves, thereby reducing plant quality
(lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to
primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic
efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin
Sandy Land.
Keywords: Lilium species, water stress, leaf photosynthesis, chlorophyll content, growth.
DOI: 10.1134/S1021443711050268
Abbreviations: Ca—atmospheric CO2 concentration; Chl—chloro�
phyll; Ci—intercellular CO2 concentration; E—transpiration rate;
gs—stomatal conductance; LCP—light compensation point; Ls—
stomatal limitation value; LSP—light saturation point; PAR—pho�
tosynthetically active radiation; Pmax—the maximum net photosyn�
thetic rate; Pn—net photosynthetic rate; PSI—photosystem I;
PSII—photosystem II; WUE—water use efficiency.
RUSSIAN JOURNAL OF PLANT PHYSIOLOGY Vol. 58 No. 5 2011
EFFECT OF WATER STRESS ON LEAF PHOTOSYNTHESIS, CHLOROPHYLL CONTENT 845
synthetic rate in soybeans, resulting in decreased plant
height, biomass, and seed yield.
Lilies are marketed as both cut and potted flowers
around the world. The oriental lily is considered as one
of the most beautiful and attractive of the Lilium spe�
cies. In China, oriental lilies are commonly grown in
mild climates and cultivated mainly in the north and
south. The Horqin Sandy Land is one of the areas
most threatened by desertification in China [9]. Plants
in this area often suffer during longer soil drought
period while water conditions are a critical factor.
Local people typically plant traditional crops that are
of low economic value. As lilies are an economically
profitable crop; the production of oriental lilies could
increase the income of people living in the Horqin
District. However, the production of both cut flowers
and potted plants is limited in scale, in part because
technologies for bulb plant management in this area
have not been validated through scientific research.
The effect of water stress on photosynthesis has been
widely studied in several crops [8, 10]. To date, studies
on the photosynthetic response of the oriental lily to
drought are scarce. It is therefore of considerable
interest to explore the effect of water stress on oriental
lilies.
A major objective of this investigation was to show
the effects of water stress on lilies. This study was
focused on photosynthetic adaptation of oriental lily
seedlings to various water treatments and describes the
effect of water stress on photosynthesis and chloro�
phyll content in terms of overall plant quality. Practical
conclusions based on our data are discussed, and gaps
in knowledge required for future research are identi�
fied. The study will help improving the cultivation and
maximization of lily growth and production in the
Horqin Sandy Land.
MATERIALS AND METHODS
The study area is located in Naiman County
(42°55′N, 120°44′E, 345 m AMSL) in the eastern
region of Inner Mongolia. Naiman County is located
in the hinterland of the Horqin District of northern
China [11]. The climate is a temperate, semi�arid,
continental monsoonal environment with an annual
mean rainfall of 360 mm, of which 75% occurs
between June and September. The annual mean latent
evaporation is 1935 mm [12]. 
The experiment was carried out in Naiman County
to determine the effects of water stress on quality, pho�
tosynthetic characteristics, and chlorophyll content of
the oriental lily cv. Sorbonne. Evenly sized lily bulbs
(12 to 13 cm in diameter) were planted in plastic pots
measuring 26 cm in diameter and 25 cm in height.
The water stress experiment was carried out during
different time periods. The lilies were planted in plas�
tic pots in a mixture of peat and sand (1 : 1), which was
fertilized with 3 g fertilizer N : P : K (4 : 3 : 2). Excess
water was allowed to drain through holes in the bot�
toms of the pots. When the plants had grown to an
approximate height of 10 cm, all plastic pots were
moved toa mobile rain shelter. During the period of
June 14 to July 24, 2009, the plants were subjected to
three different watering treatments plus a control, in
which plants were continuously watered every two
days. The three irrigation treatments consisted of irri�
gation intervals of 5, 10, and 20 days at a rate of 1500
ml water per pot. The timing and frequency of treat�
ments, as well as the sampling dates of the first treat�
ment cycle (20 days) are listed in Table 1. The second
treatment cycle (40 days) took place from July 4 to July
24, 2009. Then we ended the water stress treatments
and irrigated every treatment identically to the con�
trol. Diurnal fluctuations of photosynthetically active
radiation (PAR) (bars) and air temperature (line) for
sun light on August 7, 2009 in Naiman are represented
in Fig. 1.
Quality parameters. Five plants were used for
determination of the diameter of the flower head,
plant height, length of the flowers, and the leaf area for
every treatment at the time of the opening of the first
flower bud. 
Photosynthetic pigments determination. After the
photosynthetic activity and quality parameters were
Table 1. The time and frequency of the irrigation treat�
ments
Treat�
ment
Irrigating date
srart* 
June 14
first treatment cycle (20 days)
June 19 June 24 June 29 July 14
5 days √ √ √ √ √
10 days √ – √ – √
20 days √ – – – √
Notes: “√” irrigation, “–” no irrigation, and “*” uniformly irri�
gated.
1600
1200
800
400
6:00 8:00 10:00 12:00 14:00 16:00 18:00
45
40
35
30
25
20P
A
R
, 
µ
m
o
l p
h
o
to
n
s/
(m
2 
s)
Daytime
A
ir
 t
em
p
er
at
u
re
, 
°C
0
Fig. 1. Diurnal fluctuations of photosynthetically active
radiation (PAR) (bars) and air temperature (line) in full
sunlight on July 31, 2009 in Naiman. 
Error bars indicate ± SE (n = 3).
846
RUSSIAN JOURNAL OF PLANT PHYSIOLOGY Vol. 58 No. 5 2011
ZHANG et al.
determined, all leaves were harvested. We collected
0.1 g of fresh leaf mass to determine chlorophyll (Chl)
content. Leaves were ground in 80% acetone to extract
both Chl a and Chl b. Pigment quantities were calcu�
lated according to Lichtenthaler [13]. 
Gas exchange. Diurnal fluctuations in the net pho�
tosynthetic rate (Pn), the leaf transpiration rate (E),
stomatal conductance (gs), and the ambient CO2 con�
centration (Ci) were measured at 6:00, 8:00, 10:00,
12:00, 14:00, 16:00, and 18:00 during a day of full sun�
light (July 31, 2009) using a Li�6400 portable photo�
synthesis system (Li�COR, United States) to deter�
mine the diurnal variation in gas exchange. The ratio
of Pn to E was calculated to determine instantaneous
water use efficiency (WUE). The stomatal limitation
value (Ls) was calculated using the formula: Ls = 1 –
Ci/Ca, according to Yin et al. [5]. Measurements were
taken in situ on mature, fully expanded leaves of three
plants from each treatment [14]. Pn�PAR response
curves were measured at 2000, 1500, 1000, 500, 200,
100, 50, 20, and 0 μmol/(m2 s) PAR under uniform
conditions (30°C, 345–365 nm under full sunlight.
The linear regression of irradiance and Pn over a range
of 0�200 μmol/(m2 s) PAR was applied to determine
the compensation irradiance (LCP) [5]. The maxi�
mum net photosynthetic rate (Pmax) and the light sat�
uration point (LSP) were estimated according to Pri�
oul and Chartier [15] and Su et al. [16]. All measure�
ments were taken three times. 
All experiments were conducted in a randomized
complete block design replicated three or five times.
When significant differences were noted, the least sig�
nificant difference (LSD) test was used to separate
treatment means. All statistical analyses were per�
formed using SPSS software (standard released ver�
sion 16.0 for Windows, SPSS, United States) and
graphs were generated using the Origin 8.0 software
(United States).
RESULTS
Diurnal Variations in Leaf Gas Exchange 
Gas exchange parameters were changed with the
daytime (Fig. 2). Each parameter shared respective
similar dynamics pattern during daytime under differ�
ent water treatments. The Pn tended to decrease with
increasing irrigation intervals (Fig. 2a); it was signifi�
cantly higher in control than in water stress treat�
ments. In water stress treatments, the midday depres�
sion phenomenon was apparent. The gs and E
responded similarly as Pn (Figs. 2b, 2d); only WUE
had a different pattern: WUE increased with an
increase in irrigation intervals (Fig. 2f). The WUE was
the highest under severe water stress treatments
(20 days) and reached a peak at 14:00 (Fig. 2f). Ls
10
8
6
4
2
0
0.30
0.24
0.18
0.12
0.06
0
400
300
200
100
0
6
4
2
0
0.9
0.6
0.3
0
10
8
6
4
2
0
6:00
8:00
10:00
12:00
14:00
16:00
18:00
P
n
, 
µ
m
o
l/
(m
2 
s)
g s
, 
m
m
o
l/
(m
2 
s)
C
l, 
µ
m
o
l/
(m
o
l)
E
, 
m
m
o
l/
(m
2 
s)
L
s
W
U
E
, 
m
m
o
l/
m
o
l1
6:00
8:00
10:00
12:00
14:00
16:00
18:00
(a)
(b)
(c)
(d)
(e)
(f)
Daytime
Fig. 2. Diurnal changes in net photosynthetic rate, Pn (a), stomatal conductance, gs (b), intercellular CO2 concentration, Ci (c),
transpiration rate, E (d), stomatal limitation value, Ls (e), and intrinsic water use efficiency, WUE (f) in lily leaves at each water
stress treatment. (1) control; (2) 5 days; (3) 10 days; (4) 20 days. Error bars indicate ± SE (n = 3).
1
2
3
4
RUSSIAN JOURNAL OF PLANT PHYSIOLOGY Vol. 58 No. 5 2011
EFFECT OF WATER STRESS ON LEAF PHOTOSYNTHESIS, CHLOROPHYLL CONTENT 847
increased with the increase of water stress and
increased before 14:00 under every treatment, whereas
it decreased in afternoon (Fig. 2e).
Pn�PAR Response Curves
Water stress also affected the Pn�PAR response
curves (Fig. 3): Pn showed a pronounced decrease
when water stress rose at above 200 μmol (pho�
ton)/(m2 s) of PAR. Water stress significantly influ�
enced Pmax. The Pmax decreased with an increase in
water stress. The RD, LSP, and LCP, as well as interac�
tions among these factors, were affected by water stress
(Table 2). Under severe water stress treatments, LSP
was lower than under other water stress treatments.
The LCP and RD increased with increased water stress. 
Contents of Photosynthetic Pigments
Photosynthetic pigment content showed a significant
relationship with the level of water stress (Table 3). Water
stress decreased Chl a, Chl b, Chl (a + b) contents and
the ratio of Chl a/b.
Quality Parameters
Quality parameters exhibited significant responses
to water stress treatments (Table 4). Water stress
caused a decrease in plant height, flower length, flower
head diameter, and leaf area compared to the control
treatment. The most severe water stress treatment
(20 days) resulted in the lowest quality parameters.
DISCUSSION
Photosynthesis, which is the most significant pro�
cess influencing crop production, is also limited by
drought stress [17]. Water deficiency is one of the most
severe limitations to photosynthesis. Water deficiency
causing the closure of stomata leads to a lowered inter�
nal concentration of CO2, which in turn inhibits the
Calvin cycle, and the consequent shortage of reducible
coenzymes gives photoinhibitory conditions [18]. In
our study, water stress had a strong effect on the diur�
nal fluctuation patterns of lily leaves, which are closely
linked to the biological rhythm of the plant. The Pn, gs,
and E were reduced in plants by water stress (Figs. 2a,
2b, 2d). However, WUE significantly increased in the
water�stressed plants (Fig. 2f), which supports the
results of Brown and Pezeshki [19]. These authors
were able to show that, in addition to reduced growth,
drought led to a declinein the photosynthetic activity
of S. alterniflora due to a decrease in stomatal conduc�
tance, an inhibition of chloroplast activity, and a
breakdown of chlorophyll. An apparent Pn midday
depression phenomenon was observed in relation to
water stress at the point when PAR reached its diurnal
maximum and the temperature was high (Fig. 2a). The
midday depression phenomenon was not evident
when sufficient water was available. High PAR and
temperature may inhibit Pn by controlling stomata
closure because a similar pattern occurred with gs and
inversely pattern with Ci. The primary response of
plants to avoid drought was stomatal closure, as was,
for instance, reported for cotton [20]. The WUE is an
important index to evaluate the ability of a plant to
maintain water equilibrium by adjusting water income
and expenditure. A high WUE is an indicator of plant
adaptation to water deficiency for the purpose of water
conservation [14]. Water stress significantly increased
WUE. The control group and 5�day water treatments
showed the lower WUE. Severe water stress conditions
(20 days) increased WUE significantly. This may indi�
cate that contrasting physiological strategies are
adopted by the lilies to achieve high WUE and adapt to
drought stress. This crop response appears to be an
important mechanism for adaptation to drought [6].
12
9
6
3
0
–3
0 500 1000 1500 2000
1
2
3
4P
n
, 
µ
m
o
l/
(m
2 
s)
PAR, µmol photons/(m2 s)
Fig. 3. Photosynthesis (Pn)�PAR response curves for lily
leaves under different water stress treatments ( (1) control
group treatment, (2) 5, (3) 10, and (4) 20 days). 
 
Table 2. The maximum net photosynthetic rate (Pmax), light saturation point (LSP), light compensation point (LCP), and dark
respiration rate (RD) of the lily for the various water stress treatments
Treatment Pmax, μmol/(m
2 s) LSP, μmol/(m2 s) LCP, μmol/(m2 s) RD, μmol/(m
2 s)
Control 12 ± 2a 1367 ± 51a 40 ± 9b –2.0 ± 0.2a
5 days 7 ± 1b 1293 ± 113b 52 ± 3b –1.8 ± 0.2a
10 days 2 ± 1c 1281 ± 61b 150 ± 22a –1.5 ± 0.4a
20 days 1.0 ± 0.2c 1125 ± 20b 204 ± 12a –1.3 ± 0.1a
Note: Lines in columns denoted by different letters are significantly different at P < 0.05 according to Duncan’s multiple range tests.
848
RUSSIAN JOURNAL OF PLANT PHYSIOLOGY Vol. 58 No. 5 2011
ZHANG et al.
Photosynthetic limitation has been traditionally
analyzed in terms of stomatal limitation and nonsto�
matal limitation [7]. However, Kosobryukhov [21]
reported that the Rubisco activity, the rate of ribulose
bisphosphate (CO2 acceptor) regeneration, and the
rate of triose phosphate utilization in the Calvin cycle
were also the limiting factors for the photosynthesis
rate. In our study, reductions in Pn and gs were accom�
panied by a reduction in Ci under water stress early in
the day. But reductions in Pn and gs accompanied by
relatively high Ci values were observed after 14:00 in
the water stress treatments. The former result could
indicate that gs was the dominant factor limiting
assimilation during water stress, irrespective of any
metabolic impairment [22]. The latter result would
suggest that decreased CO2 availability to the meso�
phyll due to stomatal closure was not the principal
cause of decreased assimilation during water stress.
According to Rouhi et al. [23], an increase in Ci indi�
cates a decreased carboxylation efficiency. This indi�
cates that stomatal and nonstomatal limitations pre�
vailed for the plants during drought stress conditions.
Additionally, because water stress conditions led to
stomatal closure in the lily plant, this may result in the
reduction of Ci and thus reduced CO2 absorbability,
thus limiting leaf photosynthesis, decreasing the car�
bon assimilation capacity and photosynthetic matter
accumulation, and ultimately limiting the growth of
the lily. These results were similar to the findings of Yin
et al. [5]. Ls increased during the morning hours and
then decreased after 14:00 (Fig. 2e), suggesting that
stomatal limitation to photosynthesis was dominating
in the morning but nonstomatal limitation was domi�
nating in the afternoon. We speculate that after the
midday depression of photosynthesis, the plant needs
more time to recover.
Normally, Pmax, which determines the plant poten�
tial photosynthetic capacity, is proportional to the
number of active catalytic sites in chloroplasts that are
involved in the reductive assimilation of CO2 [7]. In
our study, a decreased Pmax and the initial slope of the
Pn�PAR response was reduced under water stress, sug�
gesting that water deficit could weaken potential pho�
tosynthetic capacity. An increase of LCP and a
decrease of LSP resulting from water stress would
reduce the time of effective Pn, and the increase of RD
would result in more consumption at night (Table 2).
Therefore, a decrease in assimilation caused by water
stress during the day and an increase in dissimilation at
night could be the main drivers of reduced plant
growth and productivity. This conclusion is in agree�
ment with the study of Wu et al. [7].
Chlorophyll content and Chl a/b ratio of leaves are
widely used to characterize the general state of the
photosynthetic apparatus [24]. Leaf chlorophyll con�
tent is one of the most important factors in determin�
ing the photosynthesis rate and dry matter production
[25]. The changes in the Chl a/b ratio are related to the
balance of the irradiance absorption capacity of the
two photosystems. Increasing Chl a/b ratio associates
with the decrease in the size of PSII light�harvesting
antenna, ensure that the supply of electrons from PSII
is sufficient to keep pace with the rate of excitation of
PSI [26]. The current study showed that the lower
photosynthetic performance of lily plants may be asso�
ciated with the decreased Chl contents under water
stress (Table 3). A decreased Chl a/b ratio was also
observed under water stress in our study (Table 3). A
Table 3. Chlorophyll (Chl a and b) content, total chlorophyll (Chl (a + b)), and Chl a/b ratio of lily leaves for each water
stress treatment (the control group treatment, 5, 10, and 20 days)
Treatment Chl a, g/kg fr wt Chl b, g/kg fr wt Chl (a + b), g/kg fr wt Chl a/b
Control 0.52 ± 0.03a 0.155 ± 0.010a 0.67 ± 0.04a 3.36 ± 0.07a
5 days 0.48 ± 0.02a 0.159 ± 0.020a 0.64 ± 0.03a 3.02 ± 0.04a
10 days 0.36 ± 0.02b 0.125 ± 0.010b 0.51 ± 0.03b 3.08 ± 0.04b
20 days 0.34 ± 0.03b 0.131 ± 0.010b 0.47 ± 0.04b 2.61 ± 0.03c
Note: Lines in columns denoted by different letters are significantly different at P < 0.05 according to Duncan’s multiple range tests.
 
Table 4. The plant height, flower length, flower diameter, and leaf area of lily at different water stress treatments (control
group treatment, 5, 10, and 20 days)
Treatment Plant height, cm Flower length, cm Flower diameter, cm Leaf area, cm2
Control 49.1 ± 0.8a 10.5 ± 0.1a 16.3 ± 0.2a 534 ± 28a
5 days 46.5 ± 0.9b 9.6 ± 0.1b 15.8 ± 0.4a 451 ± 42b
10 days 46.5 ± 0.8b 8.4 ± 0.3d 15.2 ± 0.2b 428 ± 11b
20 days 48.2 ± 0.5a 9.4 ± 0.3c 14.1 ± 0.2c 390 ± 28c
Note: Lines in columns denoted by different letters are significantly different at P < 0.05 according to Duncan’s multiple range tests.
RUSSIAN JOURNAL OF PLANT PHYSIOLOGY Vol. 58 No. 5 2011
EFFECT OF WATER STRESS ON LEAF PHOTOSYNTHESIS, CHLOROPHYLL CONTENT 849
decline in the former suggests that the photosynthetic
efficiency and PSII might be strongly affected by water
stress. A similar result has been reported in the leaf
chlorophyll content in other plants under water stress
[7, 27]. A decline in the latter suggests that water stress
might excite imbalance between PSI and PSII and
could be considered as a component of overexcitation
that might damage photosynthetic apparatus. In com�
mercial nursery production systems, frequent and
severe drought stress of container�grownplants can
reduce crop quality, delay marketing, and conse�
quently decrease profitability [28]. In our study, water
stress significantly affected the growth of lilies. The
low chlorophyll pigment (Chl a, Chl b, and Chl (a + b))
content, gs, and Pmax values, combined with lower
quality parameters (low plant height, flower length,
flower diameter, and leaf area) (Table 4), and the low
Pn of the plants grown under water stress suggests that
drought damaged the plants. This is thought to be due
to the water stress resulting in damage to the efficiency
of PSII and finally resulting in photoinhibition. These
results indicate that drought can result in damage to
the photosynthetic apparatus of oriental lilies in the
Horqin Sandy Land. The higher Pn and higher plant
quality measures (Table 4) in the control treatments
indicate that, if water is not limited, plant growth
responds positively.
In conclusion, drought stress not only significantly
decreased gas exchange (i.e., Pn, E, and gs), photosyn�
thetic pigment content, and Chl a/b ratio, and signif�
icantly increased WUE compared with the control
treatment, but also altered the diurnal gas exchange.
The Pn�PAR response curve was also affected by
drought stress. Furthermore, drought stress increased
LCP and RD, and decreased LSP and Pmax. At midday,
there was a depression in photosynthesis in water�
stressed plants, but not in control plants. There were
both stomatal and nonstomatal limitations to photo�
synthesis. Stomatal limitation was dominant in the
morning, and low Pn at midday was caused by stomatal
and nonstomatal limitation, but nonstomatal limita�
tion dominated in the afternoon. As a result, there was
a decrease in plant quality of oriental lilies during
drought stress (lower plant height, flower length,
flower diameter, and leaf area). Photosynthetic pig�
ments and Pn showed positive responses when water
was appear not limited. Thus, in order to improve the
commercial value of the lily and its production, an
appropriate water supply is recommended for the
plants so that photosynthetic processes are not
impaired in the Horqin Sandy Land region. 
ACKNOWLEDGMENTS
This study was funded by the project of Agricul�
tural Achievement Transformation (grant no.
2007GB24910484) from the Ministry of Science and
Technology of the P. R. China, the Orientation project
(grant no. KSCX2�YW�N�44�07), and the project of
Sci�Technology Sustentation Fund on Gansu Prov�
ince (grant no. KJZG�2008�3) from the Chinese
Academy of Sciences. We would also like to thank
Anne Björkman at the University of British Columbia
for her assistance with English language and gramma�
tical editing of the manuscript. 
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