沙漠研究 22-1, 5 -8 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－Mesquite (Prosopis spp.) Water Uptake
under Different Simulated Drought Conditions
Mohamed A. M. ABD ELBASIT*1) 2), Hiroshi YASUDA1), Kiyotsugu YODA3), Ahmed M. ELDOMA4),Hiroshi NAWATA5), Buho HOSHINO6) and Magzoub K. MAGZOUB2)
Abstract: The Mesquite plant has been introduced to several parts of the world in order to control land degradation and to stabilize
sand dunes. Mesquite has performed well in several locations due to its tolerance to different environmental stresses. However,mesquite is now considered one of the most invasive species in the world. In this study, we attempt to investigate the impact ofdrought on mesquite water uptake and to select plant indices that can be used to compare the mesquite’s performance under drought
conditions with that of Sudanese indigenous species.
Key Words: Growth chamber, Invasive plant species, Land degradation, Water stress1. Introduction
Mesquite (Prosopis spp.), an ever green plant, performs
ecological, economical, and hydrological roles in desert
environments. The mesquite has been classified as aphreatophytic plant since its unusually long roots give it accessto constantly saturated water reservoirs. The mesquite has
been introduced to several arid parts of the world in order torehabilitate the degraded lands and stop the continuous
encroachment of the desert. In Sudan, the mesquite wasplanted in Khartoum in 1917, and has since been established inadditional regions of the country (Babiker, 2006). Currently,
mesquite is classified as a major non-indigenous (alien species)
weed in Sudan. The mesquite pant has been shown to have
two mechanisms enabling survival under harsh, arid
conditions: phreatophytism and drought resistance. These
two mechanisms support mesquite during prolonged drought
conditions and allow it to compete successfully with the naturalindigenous species.
Consequently, mesquite displaces
indigenous plant communities, affects agricultural practices,and disturbs the eco-hydrological system in the invaded areas.
An understanding of the mesquite water uptake mechanism
could be important from an ecosystem and water conservation
point of view. Evaporation from vegetation is generally thesecond largest component of water balance (Calder, 1999).
For this reason, vegetation plays key roles in the interaction
between surface and sub-surface hydrological systems (LeMaitre et al., 1999).
The evaporation from phreatophytic plant species can bedirectly related to diurnal water table fluctuations and may
limit water resources (Tromble, 1977). The phreatophyticmechanism of the mesquite has been investigated by various
researchers (e.g. Tromble, 1977; Giordano et al., 2011). In
this study, the drought resistance mechanism will beinvestigated due to its importance in mesquite expansion inarid environments. The main objectives of this study are to
study the response of mesquite plants to different droughtlevels and to identify some plant parameters that can becompared to those of the indigenous species in Sudan andother arid environments.

2. Materials and Methods
2.1 Growth chamber and environmental monitoring
A laboratory experiment was carried out at the Arid Land
Research Center at Tottori University under a controlled
growth chamber system. The growth chamber used in thisstudy has an area equal to 6 m2. The top and side walls weretransparent to allow natural sun-light to penetrate (Fig. 1).
The chamber is equipped with a computer system which
controls the temperature, humidity, and wind speed with 95+%
accuracy. Air temperature, relative humidity, and wind speedof the chamber were fixed on 33ºC, 0.4, and 0.9 m s-1,respectively. The air temperature (T) and relative humidity(RH) were monitored at 10-minute intervals. The solar
radiation (R) was monitored using a solar radiation sensor(PYR, Decagon Devices, Washington, US), and reading weregiven every 10 minutes (Fig. 1).
The reference evapotranspiration (ET) at the growth* Corresponding Author: mbasit@alrc.tottori-u.ac.jp; m_abdelbasit@hotmail.com
1) Arid Land Research Center, Tottori University, Japan

4) Collage of Forestry Science, Sudan University of Science and Technology, Khartoum, Sudan

2) Desertification Research Institute, National Center for Research, Khartoum, Sudan

5) Research Institute for Humanity and Nature (RIHN), Japan

3) Faculty of Science and Engineering, Ishinomaki Senshu University, Japan

6) Department of Biosphere and Environmental Sciences, Rakuno Gakuen University, Japan

Fig. 2. Photosynthesis device
Fig. 1. Growth chamber.

chamber was evaluated using a 21 cm diameter steel pan filledwith water and placed on a digital scale connected to a notebook computer. The pan evaporation (Ep) was adjusted toevaluate the ETo using the following procedures:
1. The evaporation from the steel pan was converted to a
Class A evaporation pan.
E p =k sp ×Esp

(1)

where Ep is Class A water evaporation, Esp is the small panevaporation, and ksp is the small pan coefficient.
2. The Class A evaporation has been converted to ETousing relationship reported by Snyder (1992).
ETo = k p × E p(2)where ETo is reference evapotraspiration (mm day-1), kp is
the Class A evaporation pan coefficient. According to
Doorenbos and Pruitt (1977), the pan coefficient is afunction of upwind fetch distance (F), mean daily windspeed (U2), and mean daily relative humidity (RHmean).
2.2. Pots and seedling Preparation
The pot had a diameter of 25 cm with a height of 30 cm.
The pots were filled with dune sand. Four drought treatments
were used: 100, 70, 50, 25% (ET1.0, ET0.7, ET0.5, and ET0.25,
respectively) of the potential evapotraspiration evaluated by thepan evaporation. Each treatment was repeated three times.
In addition to the 12 pots of mesquite plants, three pots filled
by only sand were placed within the mesquite pots todetermine the soil evaporation. The 15 pots were arranged inblock experimental design. The mesquite seeds werecollected from Khartoum state, Sudan. The seeds weretreated using mechanical (sand paper) and chemical (using
sulfuric acid and water) techniques to break the dormancy.
Germination was induced using a small incubator for threeweeks under 27ºC temperature and artificial light. After threeweeks, the seedlings were transplanted to the pots and theinitial weight was recorded.

Fig. 3. Environmental parameters.

The weights of the pots were recorded daily prior to daily
irrigation, and water lost through transpiration (Tr) wascalculated. The amount of water added through irrigation
was determined based on the average water evaporation form
the pan. The number of leaves and the height of the plants
were recorded two times during the experiment. The
experiment was continued for two weeks. The mesquite
photosynthesis (A), stomata conductance (gs), intercellularcarbon dioxide (Ci), and leaf transpiration (Tr(L)) were measured
using Photosynthesis System LI-COR, LI 6400 (Fig. 2).

3. Results and Discussion
Figure 3 shows the T, RH, and R fluctuations during theexperimental period. The results showed that the temperatureand humidity were effectively controlled in the chamber.
However, there was some variation in the solar radiation due tosome cloudy days during the experimental period. The panevaporation was used as basis for irrigation determination andwas found to be highly correlated with solar radiation (Fig. 4).
Although the R is not included in Doorenbos and Pruitt (1977)
and Snyder (1992) equations, it showed highly impacted onpan evaporation under the chamber conditions.
3.1 Drought impact on mesquite transpiration
The mesquite transpiration has been calculated from thepots’ daily weight (Tr). The mesquite Tr decreased with theincrease of the drought level (Fig. 5). The relative decrease inFig. 4. Relationship between pan evaporation and solar radiation.
Fig. 7. Transpiration efficiency.

Fig. 5. Mesquite transpiration.

Fig. 8. Photosynthetic parameters.

level ET0.25 can be attributed to leaf defoliation in this level,although the efficiency of photosynthesis still equalled theET0.7 level (Fig. 7).

Fig. 6. Relative transpiration.

transpiration was found to be associated with drought levels(Fig. 6), which is a good indicator that mesquite is well able toadapt to water stress conditions.
There are two water uptake mechanisms that promotemesquite survival under drought conditions.
The
transpiration efficiency (TE) was evaluated based on thetranspiration calculated from the pots’ weight and mesquite
growth (Fig. 7). The plant growth was evaluated using theincrease in leaf number (TE(LN)) and plant height (TE(Hi)).
The mesquite TE increased linearly until the drought level
reached ET0.5 and then decreased in ET0.25 level. The
increase in TE can be attributed to the decrease in the amount ofwater consumed by mesquite in drought level ET0.7 and ET0.5
while the plant was able to continue its physiological activities
efficiently. This can also be confirmed by the TE calculated
based on the mesquite photosynthesis (TE(A)) under different
drought conditions (Fig. 7). The decrease in TE occurred in

3.2 Leaf level drought impact evaluation
The leaf A, gs, Ci, and Tr(L) were evaluated under different
drought levels (Fig. 8). The A, gs, Ci, and Tr(L) were similar at
ET1.0, ET0.7, and ET0.5. On the other hand, the ET0.25 resulted
in a marked decrease in A, gs, and Tr(L) (Fig. 8).
The Ci decreased slighly under ET0.25. The intrinsic water
use efficiency (WUEi) represents an indicator or ameasurement for the photosynthetic water use efficiency (Lettset al., 2010). The mesquite showed high intrinsic water use
efficiency under drought treatments compared to non-stressed
plants (Fig. 9).
The mesquite also showed high WUEi in all treatments ascompared to Acacia sp. (e.g. Acacia senegal) under different
cropping systems (Mohamed, 2005). Based on this result, theWUEi of mesquite plant under drought conditions was higher
than Acacia sp. under non-stressful conditions. The WUEi
can be used as an index for evaluation and screening of the best
species for degraded land rehabilitation (Raddad andLuukkanen, 2006). The trend for the WUEi was, generally,
increased efficiency with drought treatment, which is inACKNOWLEDGMENT
This research was financially supported by grants from
Research Institute for Humanity and Nature (RIHN), Japan(Project leader: Dr. H. Nawata) and Grant-in-Aid for Scientific
Research (B) (No. 23404014) from Japan Society for thePromotion of Science (JSPS) (Project leader: Dr. H. Yasuda).

References

Fig. 9. Intrinsic water use efficiency.

Fig. 10. Relationship between intrinsic water use efficiency and CO2ratio.

agreement with previous reported results on other plant species(Blum, 2005). The ratio between the intercellular andatmospheric CO2 (Ci/Ca) decreased with increasing drought
conditions (Fig. 9). The relationship between the WUEi and
Ci/Ca can be described by a negative linear relationship (Fig.
10).

4. Conclusions
The response of mesquite to different drought levels wasinvestigated. The mesquite showed high adaptability todifferent drought levels during a short experimental period oftime. Although the water supply was decreased by 75%, themesquite survived with high transpiration and water useefficiencies. The intrinsic water use efficiency was highcompared to Acacia sp., which gives a good explanation for
the expansion of mesquite in the Sudan. Also, a significant
relationship was found between the intrinsic water efficiency
and the intercellular and atmospheric CO2 ratio. In this study,
several plant parameters were identified for use in comparing
the performance of mesquite under drought conditions withindigenous species. The WUEi can be considered as anefficient index to be used for this purpose.

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