沙漠研究 24-1, 161-164 (2014)
Ἃ₍◊✲ 24-1, 161 -164 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫Effects of Water and Salinity Stress on the Growth of Iceplant
Tatsuya HIROKANE*1), Makoto OOBA 2), Sawahiko SHIMADA 2) and Hiromichi TOYODA 2)
Abstract: Desertification has become one of the major environmental problems of the world in recent years. Salt damage causedby saline accumulation is reported as one of the causes of desertification. There are various methods to remediate saline soil. Oneof the methods, the use of halophytic ice plant (Mesembryanthemum crystallinum), has been developed in recent years. However,studies of Mesembryanthemum crystallinum are still few and report only on the effect of salinity and moisture condition on salt
absorption and growth. The purpose of this study is to 1) elucidate salt absorption capacity and growth rate of iceplant under salinesoil, and to 2) detect the state of salt absorption of iceplant by spectral reflectance characteristics (non-destructive measurement).
According to our results, a tendency of growth reduction was found as salt stress or water stress became higher. This is presumed
because the root water absorptive function is inhibited due to the decline of soil water potential. There was a trend of higher EC
under lower soil water potential conditions. It is presumed that less soil water content activates more to salt absorption from the soil.
A trend was also found that the iceplant physiological activity declines as salt accumulation in the leaves increases. From this result,
NDVI (Normalized Difference Vegetation Index), which detects plant activity, can be a good index to show the state of saturation ofabsorbed salts. We propose that it is possible, by monitoring the leaf maximum salt accumulation with NDVI, to effectively
desalinate soil.
Key Words: Mesembryanthemum crystallinum, NDVI, Saline soil, Salt stress, Water stress1. Introduction
Desertification has become a major environmental problemof the world in recent years. Salt damage caused by salt
accumulation is reported as one of the causes of desertification.
There is estimated to be about 40 percent of the irrigated landthat has experienced soil salinization (FAO, 1997). There arevarious methods to improve saline soil. One of the recently
developed methods is the use of halophytic iceplant
Mesembryanthemum crystallinum. However, studies ofMesembryanthemum crystallinum are still few and report only
on the effect of salinity and moisture conditions on salt
absorption and growth.
Hence the objectives of this study were as follows:
1) Elucidate the salt absorption capacity and growth rate of ice
plant under saline soil.
2) Detect the state of salt absorption of ice plant by spectralreflectance characteristics (non-destructive measurement).

2. Materials and Methods
2.1. Experimental plants
Mesembryanthemum crystallinum, ice plant, is native toSouth Africa Namib Desert (Fig. 1). The main characteristics
of ice plant are known as follows, 1) it can grow in soil
* Corresponding Author: SIANN0317@gmail.com

Fig. 1. Iceplant.

Fig. 2. Bladder cells.

containing sodium chloride (ca. 3 %); 2) it absorbs salts fromthe soil, and accumulates salt into leaves and stems i.e. ice
plant generates bladder cells when absorbing salt from soil (Fig.
2); 3) it converts to the CAM type from C3 typephotosynthesis type when it encounters stress (Agarie, 2004).
2.2. Methods
In this study, irrigation amount was set in three patterns inorder to provide different soil moisture conditions. Threepatterns were set as “Poor”, “Fair,” or “Good” using soil
moisture states with pF. The pF represents a common
㸦Received, September 25th, 2013; Accepted, January 6th, 2014㸧

Tokyo University of Agriculture, 156-8502, Japan1) Graduate School of Agriculture, Tokyo University of Agriculture2) Tokyo University of Agriculture

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Fig. 3. pF vs. soil moisture curve of the sample soil.

logarithm of the height of water column soil moisture tension.
Each pF value refers to 3.9 for Poor, 3.0 for Fair, 1.8 for Good
based on irrigation amount. The irrigation amount wasdecided for each soil moisture condition from pF-moisturecurve (Fig. 3). The pF was measured by centrifugation
method and suction. Soil moisture characteristics werecontrolled according to the pF value and the moisture contentin each pF was calculated. We set salinity concentration
patterns of 0, 1, 2 and 3% in each condition by controlling
NaCl input.
The authors measured spectral reflectance and increased
amount of leaf area as indices of quality of growth until closeof experiment. We calculated leaf area to create a polygon
using a GIS by using the photos taken from directly above theplants every 6 days. We measured spectral reflectance on thetarget leaf (range is 0.26 cm in diameter) using by ASD
company spectral reflectance meter (HandHeld2) every 6 days.
Soil EC was measured to observe change of salinity in soil
every 6 days. The soil EC was measured by using EC meter(Atago) on the collected surface soil from each sample pot.
Salt concentration of the soil was estimated by measuring ECof solution of 1 : 5 in weight ratio (1: soil, 5: water), after being
dipped for 1 hour. We measured EC of leaves to observe howmuch salt ice plant absorbed every 6 days. The leaf EC wasmeasured using an EC meter (Atago) on minced leaves fromeach sample pot. Salt concentration of the leaf was estimatedby measuring EC of solution of the minced leaves of 1 : 20 inweight ratio, after dipping for 25 minutes. Both young andmature leaves were measured at the experiment end date.
The number of samples was 32 in total. Poor and Fair
irrigation had duplicated 3 samples for each treatment, while
Good irrigation had 2 samples duplication. Fair and Poor
irrigation with salinity concentration of 0, 1 and 3% treatments
were started in November 2012. Fair and Poor irrigation withsalinity concentration 2% treatment and Good irrigation withsalinity concentration 0, 1, 2 and 3% treatments were started inDecember 2012. The measurements were made every 6 days
and eight times in total.

Fig. 4. Growth trend of ice plant at the beginning and the end ofexperiment (Good irrigation treatment).

Fig. 5. Growth trend of ice plant at the beginning and the end ofexperiment (Fair irrigation treatment).

Fig. 6. Growth trend of ice plant at the beginning and the end ofexperiment (Poor irrigation).

0%3%㻌

Fig. 7. Bladder cells at the end of experiment (Good irrigationtreatment).

3. Results and Discussion
3.1. Growth trends
Figures 4, 5 and 6 show growth trend of ice plant samples.
No growth on was visually observed in the poor irrigatedcondition and 3% salinity concentration treatment. Bladdercells could be observed in all conditions (Fig. 7). As result,irrigation high salinity concentration treatment created many
bladder cells in all irrigation patterns. These results confirm theabsorbance of salts from soil into the iceplant leaves.
3.2. Soil EC transition
Figure 8 shows soil EC transition in all irrigation
conditions of salinity concentration patterns. The soil EC

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Soil water potential is lower

Fig. 8. Soil EC transition (One stage indicates 6 days).
Table. 1. Leaf area growth (from the first day to the last day).

values in poor irrigation condition were relatively low in all salt
concentration treatments. Fair irrigation condition showed
the highest EC on average in all saline treatments.
3.3. Leaf area growth
Table 1 shows measured leaf area in each irrigation
condition and saline treatment. From these results, atendency of growth reduction was found as salt stress or water
stress become higher. The salt concentration treatments
higher than 2% with less irrigation (Fair and Poor) showed nogrowth. From these, it can be observed that growth was
inhibited as soil water potential became lower and at the sametime soil osmotic potential became higher. Sodium chloride
in the soil increased the osmotic potential in the soil. This is
supposedly the cause of the growth inhibition. Furthermore,
plants are presumed to suppress their transpirationsby closing
the stomata of leaves in this dry state. Thus, photosynthesis issuppressed, and growth was reduced accordingly (Araki, 2002;
Oguchi, 2009). It is also presumed that the root water
absorptive function is inhibited due to the decline of soil water
potential.
In addition, photosynthesis type of iceplant has the ability
to convert to the CAM type from C3 type when it encountersstress. Because CAM type photosynthesis requires moreenergy, growth rate is slower than C3 type photosynthesis(Hayatsu, 2007). It is considered that the photosynthetic typeis fixed as the CAM type and the growth rate was markedly

Soil water potential is lower

Soil water potential is lower

Fig. 9. Leaf EC of both young and mature in each treated sample.

suppressed because we have set the experiment treatments inhigh stress situation.
3.4. Salts absorption characteristic
Figure 9 shows leaf EC in each irrigation and salinity
concentration pattern (on the last day). 3% concentration ofFair and Poor treatments resulted in higher EC of leaves thancompared to all other treatments. The treatments also had themost inhibited growth. The treatments also had low watercontent and high salinity in soil thus suggesting water potential
in soil was lower. Also, there was a trend of higher EC underlower soil water potential conditions in all irrigation patterns.
From these results, it is presumed that lower water content insoil can increase the salt absorption function of iceplant.
3.5. Detecting the state of salt absorption by NDVI
Iceplant leaf surface reflectances were measured using
Spectroradiometer (FieldSpec HandHeld2, ASD Co. Ltd.) andNormalized Difference Vegetation Index (NDVI) was calculated

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Fig. 10. Relationship between NDVI and leaf EC.

stressed iceplant in this study:࣭ Growth was inhibited as the water potential of the soil
became lower.
࣭ There was a tendency to absorb salts as soil water content
is lower.
࣭ NDVI detects plant activity and can be a good index toshow the state of saturation of absorbed salts and plantactivity.
As an outcome of this study, we propose that it is possible,
by monitoring the leaf maximum salt accumulation with NDVI,
to desalinate effectively saline soil.

by the following equationܰ‫ ܫܸܦ‬ൌܰ‫ ܴܫ‬െ ܴ‫ܦܧ‬ܰ‫ ܴܫ‬൅ ܴ‫ܦܧ‬Where, NIR indicates the reflectance in the wavelength
between 770 - 895 nm, and RED indicates the reflectance inthe wavelength between 630 - 690 nm.
Figure 10 shows the relationship between NDVI and leaf
EC. We can divide the activity status of leaf into two types
from the leaf EC and NDVI space (Fig. 10): Salt affected leaf
(leaf EC > 2.0 mS/cm and NDVI < 0.55) and active leaf (leafEC < 2.0 mS/cm and NDVI > 0.55). Leaf EC of more the 2mS/cm is surrounded by a black line frame and below the 2mS/cm is surrounded by a dotted line frame. From this resultof NDVI average values, there is a tendency to reduce
physiological activity by accumulating salts to the leaves.
Therefore, it is suggested that NDVI detects plant activity andcan be a good index to show the state of saturation of absorbed
salts.

4. Conclusion
We found the following outcomes on water and saline

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