全 文 ：Received 2 Aug. 2004 Accepted 9 Oct. 2004
Supported by the National Natural Science Foundation of China (90102007) and the Knowledge Innovation Program of The Chinese Academy
of Sciences (KZCX1-08-03).
* Author for correspondence. Tel: +86 (0)991 7885432; E-mail: .
① The middle and lower sections of the lower reaches of Tarim River are located in the zone between the Taklamakan Desert and Kuruk Desert,
the vegetation grew well previously in the zone, so it is called the “Green Corridor”. The National Highway No.218 passes through the “Green
Corridor”, and the planned Xinjiang-Qinghai Railway will also pass here.
http://www.chineseplantscience.com
Acta Botanica Sinica
植 物 学 报 2004, 46 (12): 1393-1401
Physiological Response of Populus euphratica to Artificial Water-recharge
of the Lower Reaches of Tarim River
CHEN Ya-Ning1*, WANG Qiang2, RUAN Xiao2, LI Wei-Hong1, CHEN Ya-Peng1
(1. Institute of Ecology and Geography, The Chinese Academy of Sciences, Urumqi 830011, China;
2. Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, China)
Abstract: Physiological and xeromorphic responses and adaptation of Populus euphratica Oliv. to
artificial water-recharge of the lower reaches of Tarim River in Xinjiang Uygur Autonomous Region were
investigated. Measurements were made of groundwater table, salt concentration in groundwater, as well as
the contents of proline, soluble sugars, plant endogenous hormone (abscisic acid, ABA and cytokinin,
CTK), and anatomic structure in P. euphratica leaves along 15 transects in three areas before and after
the water-recharge. Results showed that, following the events of water-recharge, the groundwater table
raised, which reduced the physiological stresses of P. euphratica. With the rising groundwater table, the
groundwater salinity increased by 1.76 to 2.47 folds; the thickness of cuticular of epidermis cell, the vessel
diameter and wall thickness of vascular bundle of mesophyll cell in P. euphratica leaves were reduced; but
the developmental state of palisade tissue of leaves were not affected. The effect of water-recharge was
at the optimum to the recovery and restoration of ecological environment in this region when groundwa-
ter table was raised to a range from -3.15 to -4.12 m below soil surface, and salt concentration of
groundwater maintained in a range from 67.15 to 72.65 mmol/L.
Key words: Populus euphratica ; Tarim River; physiological response; xeromorphic; water-recharge
Populus euphratica plays a very important role in main-
taining ecosystem function in arid and semi-arid regions
because of its tolerance to severe drought and high salin-
ity and alkalinity in soils. Much attention has been paid to
the capability of converse-succession-resistance in P.
euphratica forests (Gu et al., 1999; Liu et al., 2000; Zhang
et al., 2000; Chen et al., 2002), and intensive analyses have
been made to elucidate the mechanism of the converse-
succession-resistant capability of P. euphratica. Most of
previous researches, however, are concerned with tissue,
cell structure and salt tolerance of the species. There is still
a lack of full understanding of the drought-resistant capa-
bility in P. euphratica. For example, information is lacking
on the relationship between the proline accumulation in
the bodies of P. euphratica and the groundwater level.
The natural forests of P. euphratica in the Tarim River
watershed, Xinjiang, accounts for 89% of the total area in
China and 54% worldwide. The watershed is the largest
gene base of P. euphratica. Because of the intensive ex-
ploitation and utilization of water resources in the Tarim
River watershed in the past three decades, the stream flow
in a 320-km section at the lower reaches of Tarim River has
been cut off for a long time, causing the drying-up of lakes
at the river tail one after another and a severe draw-down of
groundwater levels. The problem has led to the degrada-
tion of P. euphratica forests over large areas as well as
heavy reduction of biodiversity and impairment of the eco-
system structure and functions (Huang, 1993; Chen et al.,
2003a). In order to save the “Green Corridor” ① which has
a strategic significance at the lower reaches of Tarim River,
the stream water conveyances to the lower reaches of Tarim
River for the ecology have been implemented since 2000
(artificial water-recharge, or the so-called ecological
watering), so as to increase the groundwater level and save
the increasingly degenerated natural vegetation and the
seriously damaged ecosystems (Chen et al., 2004).
The aim of the present study was to examine the physi-
ological and xeromorphic structure of P. euphratica in re-
sponse to the artificial water-recharge. Three typical areas,
respectively Yhepumahan, Alagan, and Yganbuqima, were
chosen at the lower reaches of the Tarim river (Fig.1), and
five transects were established at 100 m intervals along a
Acta Botanica Sinica 植物学报 Vol.46 No.12 20041394
vertical sampling line in each area. The groundwater table,
saline content of groundwater as well as the contents of
proline, soluble sugars, plant endogenous hormone
(abscisic acid, ABA; cytokinin, CTK) and anatomic struc-
ture of leaves were measured before and after the watering
in order to understand how the physiological processes
and the anatomic structure would be influenced by the
change of groundwater table and salinity of groundwater,
and how the plants would adjust themselves in physiology
and structure to adapt changes in environmental conditions.
It is necessary to find the optimum ecological niche of P.
euphratica under drought and salt stresses for working
out the tactics of recovery and reconstruction of ecologi-
cal environment in this district.
2 Materials and Methods
2.1 Description of the study areas
The study areas are located in the lower reaches of Tarim
River (39°38-41°45 N, 85°42 -89°17 E; Fig.1) between the
Taklamakan Desert and the Kuluke Desert. Special envi-
ronmental conditions are responsible for the fragility and
instability of ecosystems in the region. The drainage basin
is flat and the region is classified as extremely arid in warm
temperate zone. The annual precipitation varies in a range
of 17.4-42.0 mm and strong wind occurs frequently. Total
annual solar radiation varies from 5 692 to 6 360 MJ/m2,
with 2 780 to 2 980 cumulative sunlight hours. Annual accu-
mulative temperature of ≥10 °C is from 4 040 to 4 300 °C
with an average diel temperature range of 13-17 °C (Chen
et al., 2003a).
Riverbank vegetation provides a natural defense against
wind by obstructing sand movement. The famous “Green
corridor” plays an important role in keeping the national
highway 218 free of obstructions. The flora of the region
contains 14 families, 24 genera, and about 40 species of
vascular plants. The major plant species include Populus
euphratica Oliv., Tamarix ramosissima, T. hispida, Lycium
ruthenicum, Phragmites communis, Alhagi sparsifolia,
Apocynum venetum, Karelinia caspica, and Glycyrrhiza
inflata. The construction of the Daxihaizi Reservoir in 1972
reduced the water flow into the Tarim River, and dried up a
length of 321 km in its lower reaches. Two lakes in the end
of the Tarim River, the Lop Nor and the Taitema Nor, were
dried up in 1970 and 1972, respectively. The groundwater
level was lowered greatly and down to 8-12 m deep due to
the cut off of the stream flow and lack of recharge of sur-
face runoff for 30 yr. Moreover, the natural vegetation, such
as the shrub-grass vegetation dominated by Tamarix
chinensis, Halimodendron halodendron, P. communis, A.
venetum, etc., and the forests of P. euphratica relying on
groundwater for their survival and growth, have been seri-
ously degenerated, the sand dune in the sandlands be-
tween the forests have become active.
2.2 Plant source
All P. euphratica plants used this study were about
50-55 years old, 8-10 m in height, healthy and free of
infections. Care was taken to select the plants closer to
each other in each transect. South-facing leaves (exposing
to full radiation) of the plants were used for measurements.
2.3 Measurement of groundwater table
Three study areas were located respectively in
Yhepumahan, Alagan, Yganbuqima, at an interval of about
65 km each in the lower reaches of Tarim River. Five transects
of 500 m each that are parallel to the Tarim River were se-
lected at 100 m intervals along a vertical sampling line from
riverbank to sand dune in each area. Within each transect,
three wells were installed for monitoring groundwater table.
Water and plant samples were collected and analyzed in
laboratory.
2.4 Measurement of salinity in groundwater
The mean salinity of groundwater was measured by elec-
trical conductivity method. Analysis of K+, Mg2+, Ca2+ and
Na+ was conducted after digestion by HNO3 using an in-
ductively coupled argon plasma emission spectrophotom-
eter (Jobin-Yvon JY 48). The Cl- was colorimetrically deter-
mined with ferric ammonium sulphate and mercuric thiocy-
anate according to Guerrier and Patolia (1989). The total
sulfate in water was analyzed by ion-chromatography.
2.5 Proline extraction
The proline content was determined by the method of
Fig.1. Map showing study region and three areas in the lower
reaches of the Tarim River.
CHEN Ya-Ning et al.: Physiological Response of Populus euphratica to Artificial Water-recharge of the Lower Reaches of
Tarim River 1395
Troll and Lindsley (1955). Plant samples were homogenized
in 3% aqueous sulfosalicylic acid, and the homogenate was
centrifuged for 10 min at 8 000g. Supernatant was collected
for estimation of proline content. The reaction mixture con-
sisted of 0.2 mL supernatant, 2 mL acid ninhydrin and 2 mL
of glacial acetic acid, and was heated to 100 °C for 1 h. After
termination of reaction in ice bath, the reaction mixture was
extracted with 4 mL of toluene. The measurement was made
at the spectrum of 520 nm.
2.6 Analysis of soluble sugars
Fifty milligrams of freeze-dried leaves were grounded
and extracted in 1 mL of 80% (V/V) ethanol. For recovery
purposes, a known amount of ribitol was added to the ex-
tracts as an internal standard. The extracts were then boiled
for 15 min and centrifuged for 5 min at 10 000g. The super-
natant was removed and the pellet was extracted two more
times following the same procedure. The extracts were
vaccum-dried at 45 °C. The dried extracts were re-dissolved
in 1.0 mL distilled water and purified by anion exchange
Sephadex QAE-A-25 (Pharmacia Biotech, Sweden). The elu-
ates (1.0 mL extract and 2 mL water washings) were vacuum-
dried and re-dissolved in 300 mL of water. Hexose (glucose
+ fructose) and sucrose were analyzed by HPLC equipped
with a column of 300 mm ´ 7.8 mm (carbohydrate-H+,
HYDERSIL, UK) at 35 °C, H2SO4 0.005 mol/L was used as
solvent at a flow rate of 0.6 mL/min.
2.7 Extraction of plant hormone and quantification by
HPLC
Leaves (0.5 g) were grounded with liquid nitrogen. Plant
hormones were extracted in 250 mL of methanol at 4 °C
overnight in a shaking motion. Samples were then
centrifuged, supernatant was collected and dried by vacuum
and subsequently dissolved in 30 mL of 10% CH3CN. Plant
hormones were determined by HPLC. LC_10A TVP photo-
diode and ray detector (PDA), Shim pack CLC_C8 (0.15 m ´
6.0φ) were used, with flow rate at 1.5 mL/min. Detection
was made at 250 nm and 30℃. Solvent for A pump was 10%
CH3CN after the pH was adjusted to 3.0 with CF3COOH.
Solvent for B pump is 60% CH3CN. The standards of ABA
and CTK were the commercial products from Aldrich. The
peaks were identified and quantified against the external
standards.
2.8 Fixation and observation of plant cell
The leaves were fixed by FAA, dehydrated, and coated
with wax following the standard procedure, and then sliced
to a thickness of 5-8 mm. The slices were dyed with safra-
nin and light green and observation under a microscope.
2.9 Statistical analysis
Statistical analysis was carried out with the SPSS statis-
tical computer package (SPSS for windows, standard
version, release 6.1). Differences of the variables between
areas and transects were analyzed by one-way analysis of
variance (ANOVA).
3 Results
3.1 Groundwater table and salinity in groundwater
Table 1 shows the results of groundwater table and sa-
linity in groundwater before the artificial water-recharge to
the lower reaches of Tarim River, and Table 2 shows the
results after the recharge. It is apparent that the groundwater
Table 1 Groundwater table and salinity of groundwater in three areas and different transects from riverbank before the artificial water-
recharge programme in 2000
Sections
Distance from Groundwater HCO3- Cl- SO42- Ca2+ Mg2+ Na+ K+ Total salt
riverbank (m) table (m)* (g/L) (mmol/L)**
Yhepumahan 100 -5.14 0.236 1.872 0.524 0.167 0.352 1.328 0.384 37.56
200 -5.39 0.692 0.918 0.333 0.173 0.458 1.415 0.412 37.52
300 -6.36 0.704 1.372 0.354 0.115 0.292 0.817 0.217 38.15
400 -7.18 0.358 1.257 1.156 0.208 1.079 0.625 0.465 36.45
500 -7.25 0.303 1.012 0.425 0.283 0.729 1.852 0.422 35.97
Alagan 100 -6.17 0.318 1.345 0.627 0.146 0.426 1.365 0.623 37.54
200 -7.62 0.425 1.037 0.373 0.352 0.373 1.728 0.355 36.62
300 -8.19 0.467 1.725 0.254 0.637 0.429 1.645 0.274 35.54
400 -8.26 0.395 1.602 0.735 0.128 0.516 1.179 0.532 32.85
500 -9.83 0.372 1.325 0.534 0.532 0.715 1.356 0.198 31.69
Yganbuqima 100 -6.96 0.179 1.342 0.538 0.163 0.318 1.164 0.179 34.25
200 -7.65 0.256 1.105 0.624 0.113 0.275 1.532 0.635 34.63
300 -8.17 0.196 1.174 0.673 0.082 0.632 1.427 0.532 33.72
400 -8.25 0.259 1.072 0.438 0.194 0.148 1.357 0.728 33.64
500 -9.87 0.219 1.173 0.825 0.248 0.527 1.623 0.478 32.19
The values of salinity in groundwater at each transect are means of three replications. *, the values of groundwater table are means of three
replications; **, the concentration of total salt was calculated as the sum of the seven ions measured.
Acta Botanica Sinica 植物学报 Vol.46 No.12 20041396
table rose following the water-recharge in all the three ar-
eas (Tables 1, 2). The water-recharge had different effects
to groundwater table in both vertical distances to the
riverbank and the horizontal distances to the center of wa-
ter sources. The highest groundwater table and salt con-
tent in the groundwater were found at the transect 100 m
from the riverbank in the Yhepumahan area. The salt con-
tent of groundwater in different areas and transects in-
creased by 1.76 to 2.49 folds.
3.2 Change in leaf proline and soluble sugars in P.
euphratica
As shown in Fig.2, the highest level of leaf proline in P.
euphratica was observed at the transect 400 m from the
riverbank (35.62 mmol/L) before the water-recharge, and at
the transect 500 m from the riverbank (24.28 mmol/L) after
the water-recharge in the Yganbuqima area; whereas the
lowest level of leaf proline was at the transect 100 m from
the river bank (16.62 mmol/L) before the water-recharge,
and at the transect 300 m from the riverbank (9.28 mmol/L)
after the water-recharge in the Yhepumahan area.
The highest level of soluble sugars in leaves was ob-
served at the transect 400 m from the riverbank (572.02 mmol/L)
before the water-recharge, and at the transect 500 m from
the riverbank (426.73 mmol/L) after the water-recharge in
the Algan area (Fig.3); whereas the lowest level was at the
transect 100 m from the riverbank (392.60 mmol/L) before
the water-recharge, and at the transect 200 m from the
riverbank (224.71 mmol/L) after the water-recharge in the
Yganbuqima area.
3.3 Change of plant hormone content
Figure 4A indicates that, with increasing distance from
the riverbank, the ABA content in leaves of the P.
euphratica in the Yhepumahan area increased from 7.65 to
18.35 ng/g FW and the CTK content decreased from 3.25 to
0.38 ng/g FW before the water-recharge of the lower reaches
of the Tarim River. The lowest content of ABA (2.37 ng/g FW)
Table 2 Groundwater table and salinity of groundwater in three areas and different distances from riverbank two years after the artificial
water-recharge programme in 2002
Area
Distance from Groundwater HCO3- Cl- SO42- Ca2+ Mg2+ Na+ K+ Total salt
riverbank (m) table (m)* (g/L) (mmol/L)**
Yhepumahan 100 -2.66 0.367 4.853 0.792 0.235 0.355 3.792 0.455 93.48
200 -3.15 0.713 3.766 0.479 0.367 0.422 3.722 0.437 79.54
300 -3.61 0.426 3.725 0.385 0.578 0.328 3.623 0.479 72.65
400 -3.79 0.623 3.625 0.572 0.208 0.287 3.254 0.532 71.64
500 -5.74 0.307 3.547 0.478 0.209 0.298 3.221 0.278 69.38
Alagan 100 -3.16 0.357 3.887 0.655 0.239 0.379 3.654 0.427 81.54
200 -3.57 0.618 3.632 0.725 0.278 0.368 3.278 0.533 73.64
300 -4.58 0.329 3.564 0.643 0.364 0.287 3.156 0.278 68.53
400 -6.18 0.372 3.259 0.528 0.175 0.398 3.029 0.179 67.15
500 -6.82 0.462 3.617 0.674 0.438 0.277 2.997 0.352 66.25
Yganbuqima 100 -3.97 0.248 3.523 0.628 0.265 0.291 3.425 0.635 69.28
200 -4.21 0.375 3.176 0.674 0.327 0.262 3.255 0.532 67.56
300 -5.27 0.524 3.109 0.574 0.355 0.327 3.296 0.179 67.26
400 -6.83 0.179 2.994 0.633 0.427 0.423 3.155 0.354 59.45
500 -8.17 0.528 2.987 0.615 0.433 0.533 3.042 0.518 57.24
The values of salinity in groundwater at each transect are means of three replications. *, the values of groundwater table are means of three
replications; **, the concentration of total salt was calculated as the sum of the seven ions measured.
Fig.2. The content of leaf proline at different transects away from the riverbank of the Tarim River in three study areas. A. Before the
artificial water-recharge programme in 2000. B. After the artificial water-recharge programme in 2002.
CHEN Ya-Ning et al.: Physiological Response of Populus euphratica to Artificial Water-recharge of the Lower Reaches of
Tarim River 1397
and the highest content of CTK (4.67 ng/g FW) were found
in trees at the transect 100 m from the riverbank after the
water-recharge (Fig.4B).
Figure 5A shows that the ABA content of the P.
euphratica leaves displayed two peaks in the Alagan area
before the water recharge: the first (17.41 ng/g FW) at the
transect 300 m from the riverbank, and the second (21.47
ng/g FW) at the transect 500 m from the riverbank. The
CTK content was consistently at a very low level. After the
water-recharge, the ABA content increased from 3.29 to
8.64 ng/g FW and the CTK content decreased from 4.65 to
1.29 ng/g FW with increasing distance from the riverbank
to 500 m (Fig. 5B).
In Fig. 6A, two peaks were identifiable in the ABA
content in trees in the Yganbuqima area before the water-
recharge: the first (19.29 ng/g FW) at the transect 300 m
from the riverbank, and the second (24.07 ng/g FW) at the
transect 500 m from the riverbank. The CTK content main-
tained at a very low level. After the water-recharge, the
ABA content increased from 3.55 to 9.97 ng/g FW and the
CTK content decreased from 4.23 to 1.05 ng/g FW with
increasing distance from the riverbank to 500 m (Fig.6B).
3.4 Groundwater table and xeromorphic structure of the
leaves
Results in Tables 1 – 3 show that the greatest values of
cuticle thickness of epidermis cells, vessel diameter and
wall thickness of vascular bundle of mesophyll cells, and
the width of palisade tissue were 10.00 mm, 46.90 mm, 3.60
Fig.3. The content of leaf soluble sugars at different transects away from the riverbank of the Tarim River in three study areas. A. Before
the artificial water-recharge programme in 2000. B. After the artificial water-recharge programme in 2002.
Fig.4. The content of leaf hormone at different transects away from the riverbank of the Tarim River in Yhepumahan area. A. Before the
artificial water-recharge programme in 2000. B. After the artificial water-recharge programme in 2002. ABA, abscisic acid; CTK,
cytokinin.
Fig.5. Leaf hormone content at different transects away from the riverbank of the Tarim River in Alagan area. A. Before the artificial
water-recharge programme in 2000. B. After the artificial water-recharge programme in 2002. ABA, abscisic acid; CTK, cytokinin.
Acta Botanica Sinica 植物学报 Vol.46 No.12 20041398
mm, and 487.2 mm, respectively, at the transect 500 m from
the riverbank in the Yganbuqima area in 2000, before the
water-recharge programme; whereas the lowest values of
same variables were 4.20 mm, 21.20 mm, 1.49 mm, and 283.2
mm, respectively, at the transect 100 m from the riverbank in
the Yhepumahan area in 2002, after the water-recharge
programme. The amount of palisade tissues in mesophyll
cells had no relationship with the change of groundwater
table and the groundwater salinity.
4 Discussion and Conclusions
(1) Many plant species respond rapidly to stressors by
increasing the concentration of compatible solutes involved
in osmoregulation and in protection of proteins and mem-
branes under conditions of low water potential
(Shevyakova, 1983). Aspinall and Paleg (1981) summarized
the unique role of proline in plants subjected to water and
salt stress. Stress-mediated changes in proline biosynthe-
sis (Boggess et al., 1976), including hydrolysis of proteins
(Dungey and Davies, 1982) and oxidative degradation pro-
cess (Rayapati and Stewart, 1991), can result in increased
proline levels in plants exposed to different stresses. The
degradation of proline is often found to cease completely
in stressed plant materials, thus proline accumulation ap-
pears to be a widespread stress response in higher plants
(Gzik, 1996). Our results showed that free proline content
decreased at all the transects in the three research areas
and the physiologial stresses to P. euphratica had been
reduced following the water-recharge of the lower reaches
of the Tarim River. However, the increased groundwater
table was accompanied by enhanced salinity of
groundwater, hence weakening the effect of watering due
to salt stress to plants. Based on our results of the proline
accumulation, P. euphratica trees at the transect 300 m
from the riverbank in the Yhepumahan area received the
minimal impact in terms of water and salt stresses, corre-
sponding to a groundwater table of –3.61 m, total salt con-
tent in groundwater of 72.65 mmol/L, and proline content of
9.28 mmol/L in leaves.
(2) It has been widely found that carbohydrate concen-
tration increases when plants are subjected to stresses,
and that the stimulation of sugar accumulation is propor-
tional to osmotic adjustment (Sanchez et al., 1998). Under
water stress, soluble sugars may function in two ways that
are difficult to separate: as osmotic agents (Bohnert et al.,
1995) and/or as osmo-protectors (Ingram and Bartels, 1996).
As osmotic agent, the water stress-induced sugar accumu-
lation is associated with osmotic adjustment and turgor
maintenance. As osmo-protectors, sugars stabilize proteins
and membranes, most likely substituting the water in the
formation of hydrogen bands with polypeptide polar resi-
dues (Crowe et al., 1992) and phospholipid phosphate
groups (Strauss and Hauser, 1986). Sugar accumulation is
also a water stress signal in higher plants. The results of
Fig.6. Leaf hormone content at different transects away from the riverbank of the Tarim River in Yganbuqima area. A. Before the
artificial water-recharge programme in 2000. B. After the artificial water-recharge programme in 2002. ABA, abscisic acid; CTK,
cytokinin.
Table 3 Groundwater table and leaf xeromorphic structure
Xeromophic structure (X.S.)
Ground water table (G.W.T.)
-2.66 -3.15 -3.61 -4.21 -4.58 -5.14 -6.83 -7.65 -8.17 -9.87
Cuticular thickness epidermis cell (mm) 4.20 4.37 4.64 4.76 5.20 5.40 5.60 5.90 7.80 10.00
Vessel diameter of vascular bundle (mm) 21.20 23.20 24.60 26.10 32.80 33.30 34.20 34.5 36.80 46.90
Wall thickness of vascular bundle (mm) 1.49 1.61 1.86 2.32 2.43 2.47 2.68 2.70 2.70 3.60
Width of palisade tissue (mm) 283.2 312.0 330.4 420.0 408.0 391.2 494.7 366.4 452.8 487.2
Palisade tissue amount of mesophyll cell (%) 77 78 84 85 84 83 73 85 84 82
CHEN Ya-Ning et al.: Physiological Response of Populus euphratica to Artificial Water-recharge of the Lower Reaches of
Tarim River 1399
soluble sugars suggest that the stress to the P. euphratica
had been reduced after the water-recharge, and that the
plants at the transect 200 m from the riverbank in the
Yganbuqima area performed the best, which corresponded
to a groundwater table of – 4.21 m, total salt content in
groundwater of 67.56 mmol/L, leaf soluble sugar content of
224.71 (mmol/L), and leaf proline content of 11.06 mmol/L.
(3) Hormonal substances may be involved in transmit-
ting information about the water status of soil and roots to
the whole plant. As a response to water deficit, there is an
increase in the endogenous ABA levels that rapidly limits
water loss through transpiration by reducing stomatal
aperture. ABA is also involved in other aspects of stress
adaptation such as cold acclimation and root morphogen-
esis in response to stress (Campalans et al., 1999). In addi-
tion to ABA, CTK has been investigated in drought stress
studies. Masia et al. (1994) have suggested that a decrease
in CTK transport from root to shoot occurs during the on-
set of drought stress. Low CTK can result in stomatal clo-
sure of leaves (Bano et al., 1993). It has been reported that
drought could result in reduction of leaf CTK concentra-
tions in drought-susceptible cultivars of tomato (Pillay and
Beyl, 1990) and rice seedlings (Bano et al., 1993). In agree-
ment with those studies, P. euphratica trees were not able
to obtain sufficient water to maintain normal physiological
requirements under the climatic conditions of the Tarim
Basin before the artificial water-recharge programme, re-
sulting in high levels of the ABA content (from 7.65 to 24.07
ng/g FW) and low levels of the CTK content (from 1.93 to
0.17 ng/g FW) in leaves that facilitated stomatal closure to
avoid water loss. P.euphratica is highly adaptive to hyper-
arid environment, but still with a limited range. The de-
creased leaf ABA contents (from 3.59 to 9.87 ng/g FW)
increased CTK contents (from 1.05 to 4.56 ng/g FW) after
the artificial water-recharge programme suggested an im-
proved growth conditions to P. euphratica.
(4) The degeneration of P. euphratica leaves decreases
the ratio of the area to the volume of leaves and reduces the
evaporation of water. The epidermis cells of leaves are cov-
ered with thick cuticles that can prevent water loss and
penetration of harmful substances. P. euphratica leaves
have well-developed palisade tissue in mesophyll cells. The
perpendicular arrangement of the cells to the surface of the
leaf and parallel to the direction of sunlight can avoid the
strong sunlight and use the diffusive light to carry out
photosynthetic activities. These characteristics of leaf ana-
tomic structure demonstrated the adaptability of P.
euphratica to arid environment. Our results showed that
with increased groundwater table fol lowing the
water-recharge, the cuticle thickness of epidermis cells de-
creased from 10.00 mm to 4.20 mm, vessel diameter of vascu-
lar bundle of mesophyll cell from 46.90 mm to 21.20 mm, wall
thickness of vascular bundle of mesophyll cell from 3.60 to
1.90 mm, and the width of palisade tissue from 487.2 mm to
283.2 mm. The development state of palisade tissue in leaves
showed no relationship with the change in groundwater
table and the groundwater salinity. The results of anatomic
analysis again supported an improved the living status of
P. euphratica trees after the artificial water-recharge in the
lower reaches of the Tarim River.
In summery, our results suggest that the optimal range
of the groundwater table in studied region is in a range
between –3.15 and –4.12 m, which was ultimately achieved
by the artificial water-recharge programme (Chen et al.,
2003b). Outside the above range, especially higher ground-
water table, would not be appropriate for recovering the
declining P. euphratica populations of the region. In other
words, excessive water would be a loss of very important
source in such hyper-arid area and would result in the en-
hancement of secondary basicity in soil. Our study pro-
vided a scientific basis to the recovery and restoration of
ecosystems in hyper-arid areas.
References:
Aspinall D, Paleg L G. 1981. Proline accumulation: physiological
aspects. Paleg L G, Aspinall D. The Physiology and Bio-
chemistry of Drought Resistance in Plants. Sidney: Academic
Press. 215-228.
Bano A, Dorffling K, Bettin D, Hahn H. 1993. Abscisic acid and
cytokinins as possible root-to-shoot signals in xylem sap of
rice plants in drying soil. Aust J Physiol, 20: 109-115.
Boggess S F, Stewart C R, Aspinall D, Paleg L G. 1976. Effect of
water stress on proline synthesis from radioactive precursors.
Plant Physiol, 58: 398-401.
Bohnert H J, Nelson D E, Jensen R G. 1995. Adaptations to
environmental stresses. Plant Cell, 7: 1099-1111.
Campalans A, Messeguer R, Goday A, Pages M. 1999. Plant
responses to drought, from ABA signal transduction events to
the action of the induced proteins. Plant Physiol Biochem, 37:
327-340.
Chen Y-N , Li W-H , Xu H-L , Liu J-Z , Zhang H-F, Chen Y-P.
2003a. The influence of groundwater on vegetation in the lower
reaches of Tarim River, China. Acta Geogr Sin , 58: 542-549.
(in Chinese with English abstract)
Chen Y-N, Chen Y-P, Li W-H , Zhang H-F. 2003b. Response of
Acta Botanica Sinica 植物学报 Vol.46 No.12 20041400
the accumulation of proline in the bodies of Populus euphratica
to the change of groundwater level at the lower reaches of
Tarim River. Chin Sci Bull , 48: 958-961. (in Chinese)
Chen Y-N, Zhang X-L , Zhu X-M , Li W-H , Zhang Y-M , Xu H-L,
Zhang H-F, Chen Y-P. 2004. Analyses the ecological effect of
watering to lower reach of Tarim river. Sci China (Ser D), 34:
475-482.
Chen S L, Dai S X, Li J K, Wang S S. 2002. Isolation of protoplast
and ion channel recording in plasma membrane of suspension
cells of Populuse euphratica. For Studies China, 4: 1-4.
Crowe J H, Hoekstra F A, Crowe L M. 1992. Anhydrobiosis.
Ann Rev Physiol, 54: 579-599.
Dungey N O, Davies D D. 1982. Protein turnover in isolated
barley leaf segments and the effect of stress. J Exp Bot, 33:
12-20.
Gzik A. 1996. Accumulation of protein and pattern of a-amino
acids in sugar beet plants in response to osmotic, water and
salt stress. Environ Exp Bot, 36: 29-38.
Gu R-S , Jiang X-N , Guo Z-C. 1999. Structure characteristics
associated with salt tolerance of Populus euphratica. Acta
Bot Sin , 41: 576-579. (in Chinese with English abstract)
Guerrier G, Patolia J S. 1989. Comparative salt responses of ex-
cised cotyledons and seedling of pea to various osmotic and
ionic stresses. J Plant Physiol, 135: 330-337.
Huang P-Y. 1993. Desert Ecology. Urumqi: Xinjiang University
Press. 207-230. (in Chinese)
Ingram J, Bartels D. 1996. The molecular basis of dehydration
tolerance in plants. Ann Rev Plant Physiol Plant Mol Biol, 47:
377-403.
Liu Q-L , Zhang X-J , Li Y , WANG S-S , Huang Y-G , Jiang X-N
. 2000. Purification of tonoplast vescles from Populus
euphratica and its H+-pumping activity. Chin J Biochem Mol
Biol , 16: 372-376.
Masia A, Pitacco B L, Giulivo C. 1994. Hormonal responses to
partial drying of the root system of Helianthus annuus. J Exp
Bot, 45: 69-76.
Pillay I, Beyl C. 1990. Early responses of drought-resistant and
susceptible tomato plants subjected to water stress. Plant
Growth Reg, 9: 213-220.
Rayapati P J, Stewart C R. 1991. Solubilization of a prolin dehy-
drogenase from maize (Zea mays) mitochondria. Plant Physiol,
95: 787-791.
Sanchez F J, Manzanares M, Andre E F, Tenorio J L, Ayerbe L.
1998. Turgor maintenance, osmotic adjustment and soluble
sugar and proline accumulation in 49 pea cultivars in response
to water stress. Field Crops Res, 59: 225-235.
Shevyakova N Y. 1983. Metabolism and physiological role of
proline in plants under conditions of water and salt stress.
Sov Plant Physiol, 30: 587-608.
Strauss G, Hauser H. 1986. Stabilization of lipid bilayer vesicles
by sucrose during freezing. Proc Natl Acad Sci USA, 83: 2422-
2426.
Troll W, Lindsley J. 1955. A photometric method for the determi-
nation of prolin. J Biol Chem, 215: 655-660.
Zhang L , Liu Q-L , Huang Y-G . 2000. Study on purification and
activity of plasma membrane H+-ATPase of Populus
euphratica. Prog Biochem Biophys, 27: 637-640. (in Chinese)
(Managing editor: HAN Ya-Qin)