Science in China Series D: Earth Sciences
© 2007
SCIENCE IN CHINA PRESS
Springer
Impact of salt stress on the features and activities of
root system for three desert halophyte species in
their seedling stage
YI LiangPeng1,2, MA Jian1 & LI Yan1†
1
2
Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Ürümqi 830011, China;
Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Linkage between belowground and aboveground sections of ecological system is mainly depending on
root system. But root system is the parts of plant that people less understand. The absorption function
of root system is closely related to their morphology and activity. Moreover root system can interact
with the environmental stress under the adverse situation, and adjust its system to take adaptation
responses in morphology and physiology to strengthen its survival chance. This research is focused
on three desert halophyte species of H. ammodendron (C.A.Mey.) Bge., S. physophora Pall., and S.
nitraria Pall. under solution culture, to study the differences of their root system morphology and activity in the seedling stage under varying salt concentration conditions. The study results show that: A
certain salt concentration can promote development of these three halophytes; but rather high salt
concentration will restrain their growth, in particular inhibit the root system development. Under the
same salt concentration condition, S. nitraria Pall. grows fast and accumulates the largest amount of
biomass. Under relatively low salt concentration, the length of axial root and the total length of root
system of these three halophyte species are all increased; and compared to the checking samples, S.
physophora Pall. occupies the top place of root system growth, but the high salt concentration will
restrain the increase of total root length; among them, the impact intensity on S. physophora Pall. is
lighter than to H. ammodendron (C.A.Mey.) Bge. and S. nitraria Pall. is lighter; the salinity does not
bring distinct influence on the average diameter of root system of these three plant species, but trends
to reducing the size; under the solution culture conditions, the middle and lower parts of the axial root
of H. ammodendron (C.A.Mey.) Bge. and S. physophora Pall. are rather equally distributed, but the
central zone of S. nitraria Pall. root system is more significantly increased than the upper and lower
zones; salt concentration does not bring significant impact on the root system spatial distribution of
each species. The root activity of the three plants is increased along with the increase of the salt concentration. When the salt concentration is low, the root activity is not significantly increased; but when
the salt concentration is high, the root activity is increased significantly. The experimental results show
that the saline tolerance capacity of H. ammodendron (C.A.Mey.) Bge. is lower than the other two species, and the capacity of S. physophora Pall. ranks the top place.
halohyte plant, seedling stage, root system, solution culture, morphology, root activity
The process of belowground ecology system is the bottleneck of recent ecological research; also it is the most
uncertainty area of ecological function research[1,2]. The
link between the belowground process and aboveground
process of ecological system is mainly depending on
www.scichina.com
www.springerlink.com
root system to be realized. But root system, in particular
Received September 2, 2006; accepted February 26, 2007
doi: 10.1007/s11430-007-5012-7
†
Corresponding author (email: [email protected])
Supported by the National Natural Science Foundation of China (Grant No.
40471048)
Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
the fine root is the plant organs that people less under
stand[1,3]. For that the reasons are as the followings: for a
given ecological system, the morphology, architecture
distribution, etc. of its dominant plant root system will
bring certain influence to the carbon process, water balance and the bio-geochemical circulation of mineral
elements of the ecosystem[4,5]. Xinjiang is the area characterized by the driest climate, largest area of saline-alkaline soils, and the soils of heaviest salt accumulation in China[6]. Under these special physical conditions, abundant desert halo-plants are developed and
growing in Xinjiang. And it is the region with the largest
quantity of halo-plant species, and the largest halo-plant
distribution area[7]. The root system of these halo-plants
play a very important role in conserving the soils, deflate wind and water erosion[8,9].
One of the key functions of the plant root system is to
absorb water and nutrient from environment, and their
functions are closely linked with the root system morphology and activity[10]. Root activity and morphological
changes under varied environmental conditions will
bring direct influences to the plant population structure
aboveground parts, and their biomass composition[11].
Lots of research shows that plant adaptation to environment, interspecies competition, economic value, etc. are
all related to the bio-ecological characteristics of the
plant root system[12]. Because root system grow under
the ground, that is bringing difficulties to study it. But
root system is the important interface of plant to connect
soil environment, and more sensitive to the soil environment and easier to make responses[13]. Some studies
show that under the adverse environment, plant can respond to the external stress, and take physiological and
morphological adaptive reaction through regulating its
system, so as to strengthen the survival chance under the
depressed conditions[14]. The plant of phosphorus
high-effect genotype can increase its root length, root
volume, root hair and lateral root system to reduce the
root radius, but increase the contact area of the root system with soil, thereby the phosphorus absorption opportunity of the root system can be improved[15]. Foehes
discovered that the root shoot ratio of the plant of phosphorus low effect genotype is lower than that of the
phosphorus high-effective genotype plan[15]. The reaction of plant to Al stress is also firstly expressed in root
system[16,17], and root systems take the leadership in reacting to the Al stress through modifying root system
98
morphological and physiological characteristics. Through
studying the impact of Al stress on plant root system, the
plant tolerance capacity to Al stress and physiology can
be acquainted[18]. Besides, Cu, Cd, As and different
moisture and nutrient conditions also give significant
influences on root system morphology and physiology
－
of plant[19 22].
In soil the root system is the direct injured part caused
by salt and alkaline. Under the adverse conditions root
system morphology and physiology show the adaptive
characteristics and behaviors of the plant in effectively
absorbing and using nutrients of the soil[14]. Now a lot of
research of halophyte is carried out at home and abroad.
But mostly it is focused on the salt impact on the morphological and physiological characteristics of the
aboveground section of the plant, the seed germination,
etc., such as photosynthesis, transpiration, metabolic
process, salt gland, salt bladder, osmotic regulation, en－
zymatic activity, salt resistance gene[23 31]. Halo-plant
has strong capacity of salt tolerance, for which it is possible to be related with the root system morphology and
physiology. But there is no report yet on the root system
morphological features and root activity of desert halophyte under salt stress. It is waiting to carry on the approach of root system features and resistance to salt under the even salt medium condition (for example, solution culture). Now studies on root system at home and
abroad are centralized on some kind of cropping plants
and model plants, but few studies are related to the root
system of desert halophyte in the arid region.
In order to study the root system ecological reaction
of halophyte under salt stress, some representative plants
of halophytes in arid desert regions are selected for the
experimental materials of this research project. In accordance with the field soil salt conditions, solution culture was applied, through different salt concentration
treatments, to study the root system morphology and
activity of three plant species in the seedling stage. The
solution culture was adapted, because it is difficult to
screen and wash out integrity root system under direct
earth plantation or field samplings, in particular for the
fine root, the integrity root system and characteristics
cannot be fully preserved and studied. In addition, with
solution culture it can provide root system to grow in the
uniform medium and water supply conditions. In this
way, the rest disturbing factors are to be removed mostly.
Through this research project, it is aimed to ascertain the
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
1 Materials and methods
side of the plastic bucket was painted black to block the
light. Three seedlings were selected and kept in each
bucket, and the buckets were moved into the artificial
climate chamber of Conviron-PGR15 to be cultivated,
for the day time the intensity of illumination was 300
µmol photons·m−2·s−1, for the night the intensity was
zero, and the photoperiod was 14/10 h, the day and night
temperature was 25/20℃, the air relative humidity was
60%－70%, and it was aerated with electric air pump
for 24 h, all of which were to ensure the root system and
root system hair growing well.
1.1 Plant materials
1.3 Salt stress treatment
Three common desert halophyte species, which grow in
the southern zone of Guerbantonggute Sand Desert, are
selected for this test: they are H. ammodendron
(C.A.Mey.) Bge.), S. physophora Pall. And S. nitraria
Pall., and they all belong to the family of Chenopodiaceae, the succulent halophyte. The seed of the experimental plants was collected in a haloeremion, about 3
km southeast to the Fukang Desert Ecological Experimental Station, CAS in October 2005. The nutrient solution was a kind of modified Hoagland solution[32], KOH
and HCl were used to adjust the solution to pH 6.0. The
salty nutrient solution was made from Hoagland solution
mixed with NaCl, KOH was used to regulate pH.
Firstly distilled water was put into the bucket for the
seedling to adapt the growth environment for 24 h, then
it was replaced with 1/2 Hoagland solution for another
24 h, finally it was changed with full Hoagland solution.
－
Referring to the already existing research results[33 36],
three treatments were designed, of which three repetitions were set for each: checking (CK, Hoagland solution), medium salt concentration (Hoagland solution+
240 mmol·L−1 NaCl), high salt concentration (Hoagland
solution+480 mmol·L−1 NaCl). A five-day rejuvenation
period was necessary before carrying on the salt concentration treatment, then adding salt began, and it is not in
one time to add the salt to meet the concerted concentration, in consideration to adaptability of the seeding to
the high salt concentration, the salt was added to increase the concentration by degrees. The start point of
salt concentration was at the level of 80 mmol·L−1 for all
treatments, and increased by 80 mmol·L−1 per day till to
meet the scheduled concentration of 240 mmol·L−1 and
480 mmol·L−1. After reaching the scheduled concentrations, the salt stress cultivation was carried on for 30 d,
for the first period, the cultural solution was replaced
every three days, for the later period the solution was
replaced every two days, then at one time to collect all
samplings, to measure the three seedlings of each bucket
respectively, including the weight aboveground part, and
the root system weight, root system morphology, and
every indicator of root activity.
completed root system conditions of the halophyte in
seedling stage in the arid desert region, to understand the
root system morphological features and physiological
characteristics of these halophytes in adapting the saline
soil environment, and provide basic information to reveal the mechanisms of salt toleration of the halophytes
in the arid desert, as well as to establish foundations for
further studies on the root system conditions of these
halo-plants under natural environment.
1.2 Cultural conditions
Full uniform seed was selected, soaked with 10% H2O2
for 30 min, and then washed with distilled water repeatedly to clean H2O2, and till no H2O2 residual left. The
treated seed was separately put into Petri dish, which
was paved with abacterial filter paper. Then the seed
with Petri dish was placed into an incubator with 25℃
to accelerate germination until emerging bud white, then
the even germinating seeds were chosen and placed into
a plastic container, in which were contained cleaned
vermiculite and quartz sand (mixed scale of volume
V/V:2/3) to raise seedling, firstly distilled water was
used to culture the seeds to seedling emergence, after
that, 1/2 Hoagland solution was used for cultivation,
when the seedling was growing to about 2 cm length, the
same size seedling was chosen and cleaned with distilled
water, and then shifted into a plastic bucket, which was
30 cm tall and 20 cm in diameter for further cultivation,
the base part of the seedling was wrapped with absorbent cotton, foam plastic board was put in the upper part
of the plastic bucket to be the supporting materials, out-
1.4 Measuring the weight of aboveground part and
root shoot ratio
After 30 d salt concentration treatment, the full integrity
plant was taken out from the cultural bucket, and then
fast washed with distilled water three times. These
plants was divided into the belowground part and
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
99
aboveground part, then the fresh samplings were put into
the oven with 105℃ for water-removing for 30 min, and
the temperature was turned to 80℃ for 24 h to get constant weight and measure the dry weigh. Root shoot ratio＝dry weight of root system:dry weight of the aboveground part.
time. The method of Li Hesheng was consulted for root
activity measuring (TTC reduction)[39]. The root activity
was expressed with TTC reduction intensity, the reduction intensity per fresh weight of root system = the
weight reduction in TTC divided by (root system weight
× time), with the unit as mg·(g·h) −1.
1.5 Measuring the root activity
1.6 Data analysis and processing
We took out the full seedling from the cultural bucket to
wash the root system with distilled water three times,
and then put the cleaned root system into 50℃, 1%
crystal violet solution for 5 min. After the root system
was pulled out, it was washed with distilled water for
2 min to get rid of the redundant crystal violet. Then the
root system were put into 50% ethanol, and preserved in
a refrigerator. After all samplings were dyed, we started
scanning. Before scanning, the root system was washed
with distilled water one more time, the root system was
then put into a glass dish with a NaOH solution of 0.01
mol·L−1 (the solution was about 0.5 cm in depth). High
pH prevented the dyestuff from extravagating out of the
root system. We use forceps and tooth pick to spread out
the root system completely, to avoid overlapping and
touching each other. After then, scanning was done as
quick as possible, to prevent dyestuff from oozing under
high temperature. White and Black binary image, 600
DPI resolution and 100% scale was selected for scanning. After scanning, the images were subset into several small images, we kept the integrity of smallest root
system. The images were saved in TIFF format for final
analysis. The software of Rootedge2.3b was used to obtain the total length and average diameter of the root
system. Rootedge was a piece of free software developed by Iowa State University, USA, and it was similar
to WinRHIZO, and was widely used in root morphological parameter analysis[37,38].
We selected healthy fresh white root as the materials
for measuring the root system activities, for healthy root
system is all fresh white, and viable. When measuring,
the root system was fetched from the same seedling each
The data were processed with SPSS 12.0, and Origin 7.0
was used for making figures.
2 Results and analysis
2.1 Impact of salt on plant growth in root and shoot
ratio
Under solution culture, different NaCl concentration
treatment brought remarkable difference on the growth
of the three plant species (Table 1). With the treatment
of 240 mmol·L−1 NaCl, the biomass of aboveground part
of the three plants was increased compared to the control
samples. The biomass increase of S. physophora Pall.
was significant, showing that the proper increase of the
salt concentration was favorable to the plant growth. As
these three species are succulent halophytes, they need
certain salt for normal growth, S. physophora Pall. needs
more salt than the other two. With the treatment of 480
mmol·L−1 NaCl, the biomass of the aboveground part of
the three plants and root system were all decreased
compared to that of control, and the reduction of the
aboveground part of H. ammodendron (C.A.Mey.) Bge.
and S. nitraria Pall. reached significant level. With the
treatment of 240 mmol·L−1 NaCl, the root biomass was
more obviously reduced compared to the control, but the
difference was not significant. With the treatment of
NaCl at 480 mmol·L−1, the root system biomass was
reduced more evidently than that of the aboveground
part of the plant, and the amount of biomass reduction of
the three plants all reached significant level. The root
biomass reduction of H. ammodendron (C.A.Mey.) Bge.
and S. nitraria Pall. reached very significant level. These
Table 1 NaCl impact on the biomass of the above ground part and root system of the three halophytes
NaCl concentration
(mmol·L−1)
0 (CK)
240
480
Dry weight of the aboveground part (g·seedling−1)
H.ammodendron
S.physophora
S.nitraria
(C.A.Mey.) Bge.
Pall.
Pall.
0.1198 aA
0.1744 aA
1.0251 aA
0.1210 aA
0.1892 bA
1.0310 aA
0.0957 bB
0.1621 aA
0.9165 bA
Dry weight of root system (g·seedling−1)
H.ammodendron
S.physophora
S.nitraria
(C.A.Mey.) Bge.
Pall.
Pall.
0.0276 aA
0.0719 aA
0.2213 aA
0.0254 aA
0.0733 aA
0.2206 aA
0.0183 bB
0.0618 bA
0.1781 bB
a, b indicate significant differences between halophyte types at p < 0.05 level (SSR); A, B represents highly significant differences between halophyte
types at p < 0.01 level (SSR), and the same as in the following.
100
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
showed that the high salt concentration had severe impact on the root growth of H. ammodendron (C.A.Mey.)
Bge. and S. nitraria Pall. With high salt concentration,
the biomass reduction of the aboveground part and root
system of S. physophora Pall. was small, which indicated that the salt resistance ability of S. physophora
Pall. was higher compared to that of H. ammodendron
(C.A.Mey.) Bge. and S. nitraria Pall. Under the treatment of high NaCl concentration at 480 mmol·L−1, the
biomass of H. ammodendron (C.A.Mey.) Bge. was more
evidently reduced, both for the aboveground part and root
system, which showed that its salt tolerance was lower
than that of S. nitraria Pall. and S. physophora Pall.
Different parts of the seedling also showed different
responses to salt stress. The root/shoot ratio of the salt
treated plants was all lower than that of the control, and
this difference was enlarged with the increase of salt
concentration (Figure 1). Under the conditions of NaCl
at 240 mmol·L−1, the root/shoot ratios of the three plants
were all declined, but there was no significant difference
compared to the control. But at 480 mmol·L−1 level of
NaCl, the root shoot ratio reduction of H. ammodendron
(C.A.Mey.) Bge. and S. nitraria Pall. reached significant
level. That showed that with salt treatment, the photosynthesis product supply to the belowground part was
reduced, so the growth suppression of the belowground
part was more severe than that of the aboveground part.
As for the total biomass of the aboveground part and
root system, S. nitraria Pall. ranked the first place, S.
physophora Pall. occupied the second, and H. am-
Figure 1 Impact of different NaCl concentrations on the root shoot
ration of the three halophytes (mmol·L−1).
modendron (C.A.Mey.) Bge. the third. Both the biomasses of the aboveground part and root system of S.
nitraria Pall. were larger than that of the other two
plants, which showed its fast growing in the seedling
stage, because S. nitraria Pall. is an annual herbage
plant, and its life cycle must be finished in one growing
season, so it has to grow fast in the seedling stage and
achieve the full development in a short time. In the test
with different salt concentrations, there was the negative
correlation between the root/shoot ratio and salt concentration: the root system occupying less assimilation materials in a given extent, the degree of the salt stress on
the plants is higher.
Root system is the main organ to absorb water and
nutrients. Compared to the aboveground part of plant, it
is necessary to use as much as double amount of energy
for root system to produce the same unit of dry matter[40].
If the root/shoot ratio is high, assimilation product must
distribute more to the root system, and this is favorable
for root expansion. According to our experimental results, the root shoot ratio of S. physophora Pall. in the
seedling stage was high, indicating that its root system
was expanding rather fast; accordingly the root system
competed with the aboveground part for more photosynthesis products, so as it reduced the distribution of
carbohydrate to the aboveground part, and affects the
growing rate of the aboveground part. Some researchers
discovered that the increase of root shoot ratio will enhance absorption of water and nutrient, and strengthen
the capacity of plant in drought resistance and poor soils,
which was helpful for plant to adapt to harsh environments[41,42]. These results show that the increase in
root/shoot ratio is a kind of adaptation of halophyte to
the salty environment, and the variation of the ratio of
different halophyte plants represents the varied adaptation capability to the salty habitat. The relations between
growth and osmotic environment were clearly reflected
in the root system. As a result, the root growing declination will lower nutrient absorption, and in turn it will
depress the growth of all plant organs. Normally, the
root/shoot ratio of non-halophyte is larger than that of
halophyte[43]. Based on this test, it can be inferred that
among the helophytes, the one with higher salt toleration
capacity will have a larger root shoot ratio.
2.2 Impact of salt on the root system morphological
features
With the three level treatment conditions of NaCl con-
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
101
centration, remarkable change of the root morphology
took place, among which, the total length of the root
system was the most (Table 2). Different salt concentrations did not have much impact on the axial root length,
especially when the salt concentration was low. Under
the treatment of NaCl solution at 480 mmol·L−1, the axial root length was more significantly reduced compared
to the control. The axial root decrease of H. ammodendron (C.A.Mey.) Bge. and S. nitraria Pall. reached the
significant level, showing that high NaCl concentration
inhibited axial root growth. With low salt concentration,
the total root length of H. ammodendron (C.A.Mey.)
Bge. was more significantly increased compared to the
control; but under the high salt concentration, its total
root length was highly reduced; all of which show that a
certain salt concentration could promote the root growth
of H. ammodendron (C.A.Mey.) Bge., but the high salt
concentration will inhibit its root growth. The response
of S. nitraria Pall. was similar. With 240 mmol·L−1 NaCl,
the total root length of S. physophora Pall. was clearly
increased, and reached highly significant level, indicating that a certain salt concentration is favorable to the
root development; but under the environment of 480
mmol·L−1 NaCl solution, root development was inhibited,
with the impact less significant than that on H. ammodendron (C.A.Mey.) Bge. and S. nitraria Pall. The
total root length and average root diameter of S. nitraria
Pall. were larger than that of the other two plants, which
was in agreement with the dry weight of root system.
Namely, overall, its root system grows faster than the
other two species. Different NaCl concentrations did not
have significant influence on the average diameter of
root system, although with a slight tendency of decrease
with the increase of salt concentration. Among the three
species, the average root diameter of S. nitraria Pall.
decreased the most.
As to the root morphological indicators, salt had impact on the axial root length, the total root length and
average root system diameter of individual seedling.
Within the current range of the salt concentration, the
total root length responded the most, for the total root
system length consisted of the axial root, lateral root
system and branched root system, and thus it represented
the integrated response of the root system. Hence, the
total root length of a seedling can be taken as a primary
indicator, when salt stress study on plant root system is
concerned
2.3 Impact of salt on root distribution
There were differences in the root distribution of these
three plant species at different zones (Figures 2 and 3).
At 0－4 cm depths, axial root system was important part
of overall root system for all three species; the total
length of root system is almost solely the axial root
length. As for H. ammodendron (C.A.Mey.) Bge., below
4 cm, there was not much difference in average root
diameter and total root length, showing that after 4 cm,
the root was distributed uniformly, and mostly their diameters were less than 0.4 mm. The similar situation
happened to the root distribution of S. physophora Pall.,
but the root system was in deeper zones ( mainly below
8 cm), with diameters of most root system less than 0.5
mm. The root system of S. nitraria Pall. was larger, but
its root system was mainly in the range of 16－24 cm,
the zone of middle depth; with most of the root diameter
smaller than 0.6 mm. That also explains the quick development of S. nitraria Pall.: its root system at middle
depth was rapidly extending. Generally speaking, under
solution culture, the root system of the three plants in the
seedling stage consisted mainly of fine root system (the
diameter smaller than 1 mm), and there was not much
change for their diameters of the root system, with their
distribution also uniform. Because they were all desert
halophyte, through reducing the root diameter and increasing the length of root system, they could absorb
water and nutrient from large area in order to support
their growth. Figures 1 and 2 show that the salt concentration did not have significant impact on the root distribution of the three plants, and under the high salt
concentration conditions, only the total length of each
part of the root system was reduced.
Table 2 NaCl impact on the root system morphological key parameters of the three halophytes
NaCl
Length of axial root (cm)
Total length of root system (cm)
concentration H.ammodendron S.physophora S.nitraria H.ammodendron S.physophora S.nitraria
(mmol·L−1) (C.A.Mey.) Bge.
Pall.
Pall.
(C.A.Mey.) Bge.
Pall.
Pall.
0 (CK)
12.0 aA
24.0 aA
35.2 aA
544 aA
1455 aA
2274 aA
240
13.5 aA
29.2 bA
36.0 aA
615 bA
2123 bB
2632 bB
480
9.2 bB
22.3 aA
32.0 bA
447 cB
1367 aA
1870 cC
102
Average root diameter (mm)
H.ammodendron S.physophora S.nitraria
(C.A.Mey.) Bge.
Pall.
Pall.
0.35 aA
0.42 aA
0.55 aA
0.35 aA
0.40 aA
0.55 aA
0.32 aA
0.40 aA
0.45 bA
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
genises, which is related to respiration. So reducing capacity of TTC is comparatively correlated with respiration intensity[45], and can be used to measure the respiration capacity of plant materials. In the salinity-alkali and
drought environment, plants deplete energy for osmotic
regulation and maintaining osmotic potential[46,47] . After
salt treatment, the root activities of the three plants were
all higher than the control (Figure 4). With 240 mmol·L−1
NaCl treatment, the root activity of H. ammodendron
(C.A.Mey.) Bge., S. physophora Pall. and S. nitraria
Pall. was not increased much, 4.3%, 2.7% and 5.5% respectively compared to control; but with 480 mmol·L−1
NaCl, their root activities were increased by 52%, 28%
and 36% respectively, and the differences were all at
significant level (P<0.05).
Figure 2 The total root length of the three helophytes in different depths
of the solution, in different NaCl concentrations.
Figure 4 Impact of different NaCl concentrations on the root activity of
the three halophytes (mmol·L−1).
Figure 3 The average root diameter of the three halophytes in different
depths of the solution, with different NaCl concentrations.
2.4 Impact of salt on root activities
The root activity generally refers to absorption ability,
synthesis ability, oxidizing ability, reducing ability, etc.,
which objectively reflect the physiological index of living activities of the root system[44]. The capacity of reducing TTC is an index to measure succinct dehydro-
Drought stress, salt stress and salt-alkali stress all can
spur root activities[44]. Therefore, the root activity increase and the respiration rate increase can be considered as the plant reaction to adverse environment. Of
course, this kind of reaction consumes large amounts of
nutrient materials[45,46]. In this experiment, along with
the increase of the salt concentration, the root activity of
the three plants was increased (Figure 4). The dry
weight of a single seedling was reduced under the high
salt concentration treatment (Table 1), and the root/shoot
ratio was declined (Figure 1). All of these showed that
under salinity environments, the halophyte root system
consumed large amounts of nutrient to increase the respiration rate to resist salt stress. Consequently, the nutrient materials distributed for growing was reduced, and
its growth was inhibited, especially for the root system
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
103
(Table 1; Figure 1). Therefore, under the salt stress, the
increase of halophyte root activities has two meanings:
one is the active response of the halophyte in salt toleration; the other is to pay the cost in reducing growing rate
to enhance its salt resistance capacity.
Among the three plants, the root activity of H. ammodendron (C.A.Mey.) Bge. was increased to the largest
extent under the high salt concentration treatment, which
means that it consumed a large amount of nutrient to
enhance root respiration. Consequently, the root dry
matter accumulation declined, which was in agreement
with the low root/shoot ratio of H. ammodendron
(C.A.Mey.) Bge. mentioned above. But under high salt
concentration, the increase of root activities of S.
physophora Pall. was rather small, indicating its higher
salt toleration capacity. All of these indicated that root
activity is an important aspect in reflecting halophyte
salt resistant capacity.
Root system is the main organ of plant to absorb water and nutrient, also it is the first key part to receive the
adverse stress in soils. Under adverse stress, plant often
modifies its root morphology and distribution to adapt to
unfavorable growth environment[47]. The total length of
root system, average diameter of root system, dry weight
of root system and activity of root system are the indices
to reflect root development conditions[48]. Salt has significant impact on the total length of root system and dry
weight of root system of the halophyte. Salt clearly enhances the activity of plant root system. As a result, the
ways of salt impact on the root system development of
halophyte are complicated, as result of the multivariate
physiological and biochemical responses of plant under
salt impact.
Previous studies[49,50] and this research show that,
certain salt concentration will promote halophyte development, and only excessive salt harms such plant, i.e.
there is a question of the threshold on salt influence to
such plant. When the salt concentration is below the
threshold, it can stimulate plant development; when salt
concentration exceeds the threshold, it will bring damage to plant; and different plants have different salt
thresholds. In this study under solution culture, with the
treatment of 240 mmol·L−1 NaCl, all results in root,
morphology and physiology indicated that it was favorable to the development of these three halophytes. With
the treatment of 480 mmol·L−1 NaCl, all the results indicated the development of the halophyte were inhibited.
104
Namely, under solution culture, the threshold of NaCl
impact on the three plants is larger than 240 mmol·L−1.
Based on the index of S. physophora Pall., it is supposed
that its salt impact threshold is the highest among the
three plants studied in this research.
3 Conclusions
Based on this research of the salt treatment impact on
the root system features and activity of the three desert
halophytes in the seedling stage, which was carried out
under solution culture, the followings can be concluded:
(1) Certain salt concentration can promote the development of the three halophytes, but high salt concentration will inhibited their growth, especially on root
development. With the increases of salt concentration,
the root shoot ratio decline was enhanced. Under different salt concentration conditions, the root shoot ratio
showed a negative correlation to the salt concentration.
The development rate of S. nitraria Pall. in the seedling
stage, both for the root system and aboveground part,
were higher than the rate of H. ammodendron
(C.A.Mey.) Bge.and S. physophora Pall.
(2) With relatively low salt concentration, the axial
root length and the total length of the root system of the
three halohyte plants were all increased, among which
the root lengths of S. physophora Pall. were more
greatly increased. And the high salt concentration will
also restrain the root system growth, but the inhibitory
degree to S. physophora Pall. was lighter than that to H.
ammodendron (C.A.Mey.) Bge. and S. nitraria Pall. Salt
concentration does not have clear impact on the diameter of the three plants root system. Under solution cultural conditions, the root system of H. ammodendron
(C.A.Mey.) Bge. and S. physophora Pall. was uniformly
distributed in all the upper, middle and lower parts, but
for S. nitraria Pall., the root system in the middle zone
was more significantly increased than in the upper and
lower zones. Salt does not have significant influence on
the root distribution of the three plants.
(3) The root activity of the three plants was increased
with the salt concentration increase. When the salt concentration was relatively low, the root activity was not
clearly increased; but under the high salt concentration,
the activity increase was highly significant, for increase
of the root activity is the response of the plant in adapting to the adverse environment, which will in turn consume large amounts of nutrient materials, thus it will
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
lead to the reduction of the plant dry weight. This coincides with the biomass declination of these three plants
under high salt concentration. According to the current
study, it can be concluded that among the three halophytes, the salt tolerate capacity of H. ammodendron
(C.A.Mey.) Bge. is weaker than that of the other two,
and the salt toleration capacity of S. physophora Pall. is
the highest.
The current study on root morphology and activity of
the three halophytes in the seedling stage, quantified the
salt toleration capacity of these three halophytes, and
laid down certain foundation for the further study on the
root system of these plants in the natural native inhabit.
For the future research, more desert halophyte species
should be selected for test, and the range of salt concentration should be enlarged.
Copley J. Ecology goes underground. Nature, 2000, 406: 452－454
[DOI]
sholtzia argyi. J Soil Water Conserv (in Chinese), 2005, 19(3):
1
2
Chapin F S, Ruess R W. The root system of the matter. Nature, 2001,
411: 749－752[DOI]
3
morphology and Cu accumulation of Elsholtzia splendens and El-
20
Morgan J A. Looking beneath the surface. Science, 2002, 298:
growth and metabolism of the wheat root system. Acta Ecol Sin (in
1903－1904[DOI]
4
Schlesinger W H. Biogeochemistry: An Analysis of Global Change.
5
He J S, Wang Z Q, Fang J Y. Issues and prospects of belowground
21
San Diego, California, USA: Academic Press, 1997
ecology with special reference to global climate change. Chin Sci Bull,
Acta Agron Sin (in Chinese), 2004, 30(11): 1145－1151
22
7
Ji Q C, Zhou M Y, Zhang F X. Effects of coupling of water and fertilizer on morphological characteristics and activity of root. J Water
Zhang B Q. Soil Stalinization and its prevention in Xinjiang. Arid
Zone Res (in Chinese), 1993, 10(1): 66－71
Chinese), 2004,30(11): 1145－1151
Li Y X, Ma G R. Physiological and morphological characteristics of
root system in grain amaranth genotypes enrichment in potassium.
2004, 49(18): 1891－1899
6
97－100
Zhu Y J, Wang C Y, Ma Y X, et al. Effect of arsenic stress on the
23
Zhou S, Han J L, Zhao K F. Advance of study on recretohalophytes.
Resourc Archit Engin (in Chinese), 2005, 3(3): 17－21
Lu G, Jiang B, Wang T K. Photosystem II photochemistry and photosynthetic pigment composition in salt-adapted halophyte Artimisia
Chin J Appl Environ Biol (in Chinese), 2001, 7(5): 496－501
anethifolia grown under outdoor conditions. Plant Physiol, 2003, 160:
8
Huang P Y. Excused Irrigation Vegetation in Desert and Its Restora-
403－408[DOI]
9
tion (in Chinese). Beijing: Science Press, 2002. 65－73
Waldron L J, Dakessian S. Effect of grass, legume, and tree root
24
accumulation in the halophyte Salvadora persica grown at moderate
system on soil shearing resistance. Soil Sci Soc Am J, 1982, 46:
894－899.
10
25
Zhang L, Li J M, Wang H X. Physiological and ecological responses
11
26
Davies W J, Zhang J. Root signals and the regulation of growth and
12
27
Sun X, Yu Z. A study on root system of Nitraria Tangutorum. J Desert
Lynch J P. Root architecture and plant productivity. Plant Physio1,
14
1995, 109: 7－l3
Feng F, Zhang F S, Yang X Q. Plant Nutriology — Advances and
Prospects (in Chinese). Beijing: China Agricultural University Press,
28
29
Acience) (in Chinese), 2004, 22(6): 500－503
30
Rengel Z. Disturbance of cell CO2 homeostasis as primary trigger of
Kollmeier M, Felle H H, Horst W J. Genotypic difference in Al re-
31
nara cardunculus. Plant Sci, 2005, 168(5): 653－659
Shen Y G, Chen S Y. Molecular mechanism of plant responses to salt
32
stress. Hereditas (in Chinese), 2001, 23(4): 365－369
Pan R Z. Plant Physiology (Fourth Edition) (in Chinese). Beijing:
33
Zhao K F, Har P J C. Study on the chemical message from the root
sistance of maize are expressed in the distal part of the transition zone.
Plant Physiol, 2000, 122: 945－956[DOI]
18
Deborah A, Tesfaye M. Plant improvement for tolerance to aluminum
in acid soils—a review. Plant Cell Tiss Org, 2003, 75: 189－207
[DOI]
19
Tian S K, Li Y X, Peng H Y et al. Influence of Cu toxicity on root
María Benlloch González, José María Fournier, José Ramos et al.
Strategies underlying salt tolerance in halophytes are present in Cy-
toxicity syndrome. Plant Cell Environ, 1992, 15: 931－938[DOI]
17
Chinese), 2005, 41(3): 383－387
Sun L, Xiao L. Studies on the activity and isozyme of superoxide
dismutase in chenopodiacea saline species. J Shihezi Univ (Natural
Foehes D, Claassen N, Jungk A. External and internal P requirement
and P efficiency of different plant species. Plant Soil, 1988, 110: 10－19
16
463－499[DOI]
Cai L, Zhang F C. Cloning and sequence analysis of NHX genes from
three species of halophytes from Xinjiang. Plant Physiol Commun (in
2000. 12－21
15
justment. Acta Botan Sin (in Chinese), 1999, 41(12): 1287－1292
Hasegawa P M, Bressan R A, Zhu J K, et al. Plant cellular and molecular responses to high salinity. Annu Rev Plant Phys, 2000, 51(2):
Res (in Chinese), 1992, 12(4): 50－54
13
nese), 2002, 33(12): 170－173
Zhao K F, Li J. Effects of salinity on the contents of osmotic of
monocotyledonous halophytes and their contribution to osmotic ad-
development of plant in drying soil. Annu Rev Plant Phys, 1991, 42:
55－76
salinity. Environ Exp Bot, 2000, 44(1): 31－38
Li H Y, Zhao K F. The inhibition of salinity on the germination of
halophyte seeds. J Shandong Agric Univ (Natural Science) (in Chi-
of wheat (Triticum aestivm L.) root to cadmium stress. Chin J Soil Sci
(in Chinese), 2002, 33(1): 61－65
Albino M, Muppala P R, Robert J J. Leaf gas exchange and solute
Higher Education Press, 2001. 28
system under salt stress. J Shandong Normal Univ (Natural Science)
(in Chinese), 1992, 7(4): 96－100
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106
105
solutes of halophyte Suaeda salsa seedlings under the stress of NaCl.
43
standing of soil science? Eur J Soil Sci, 2005, 56: 1－11[DOI]
Zhao K F, Fan H. Halophytes and Their Adaptive Physiology to Salt
35
Acta Patac Sinica (in Chinese), 2005, 14(1): 63－68
Mass E V. Saline tolerance of plant. Prog Pedology (in Chinese),
44
Sechenbater, Wu H Y. Effect of different stress on root activity and
36
1988(2): 36－51
Li P F, Bai W B, Yang Z C. Effects of NaCl stress on ions absorption
34
Duan D Y, Liu X J, Li C Z. The effects of nitrogen on the growth and
and transportation and plant growth of Tall Fescue. Scientia Agric Sin
Habitat (in Chinese). Beijing: Science Press, 2005. 72
nitrate reductase activity in Zea mays L. Agric Res Arid Areas (in
Chinese), 2001, 19(2): 67－70
45
Zhao K F, Li F Z. Halophyte of China (in Chinese). Beijing: Science
46
Press, 1999. 173－177
Xu Y L, Yu S W. Energy consumption of plant in the course of
(in Chinese), 2005, 38(7): 1458－1465
37
Himmelbauerl M L, Loiskandl W, Kastanek F. Estimating length,
average diameter and surface area of root system using two different
adaption to salt stress. Plant Physiol Commun (in Chinese), 1990, (6):
Image analyses systems. Plant Soil, 2004, 260: 111－120 [DOI]
38
Kaspar T C, Ewing R P. ROOTEDGE: Software for measuring root
70－72
47
length from desktop scanner images. Agron J, 1997, 89: 932－940
39
Li H S. The Experimental Principle and Technology of Plant Physiology and Biochemistry (in Chinese). Beijing: Higher Education Press,
40
41
106
sourc (in Chinese), 2003, 4(3): 265－269
Cui G X, Li Z D. Relationship between potassium and root parameters
of genotypes of ramie. Res Agric Modern (in Chinese), 2000, 21(6):
49
Xu B C, Shan L, Huang J. Comparison of water use efficiency and
root/shoot ratio in seedling stage of switchgrass and old world blue-
42
48
2000. 119－120
Passioura J B. Root signals control leaf expansion in wheat seedlings
growing in drying soil. Aust J Plant Physiol, 1988, 15: 687－693
Zeng Y, Gai J Y, Lu H N. Advances of the relationship between crop
root morphology and tolerance to antibiotic stress. J Plant Genet Re-
371－375
Jiang G M. Plant Physioecology (in Chinese). Beijing: Higher Education Press, 2004. 203
50
Yi Y J, Liu J Y, Ma Z Q, et al. Comparative Study of Effects of NaCl
stems under different soil water conditions. Acta Patac Sin (in Chi-
on Betaine Levels and Betaine-aldehyde Dehydrogenase Activity in
nese), 2003, 12(4): 73－77
Gregory P J. Root, rhizosphere and soil: the route to a batter under-
Halophyte and Nonhalophyte. J Qufu Normal Univ (Natural Science)
(in Chinese), 1995, 21(1): 69－73
YI LiangPeng et al. Sci China Ser D-Earth Sci | June 2007 | vol. 50 | Supp. I | 97-106