Potential of nine multipurpose tree species to reduce saline

Agroforest Syst
DOI 10.1007/s10457-006-9006-9
Potential of nine multipurpose tree species to reduce saline
groundwater tables in the lower Amu Darya River region
of Uzbekistan
Asia Khamzina Æ John P. A. Lamers Æ
Christopher Martius Æ Martin Worbes Æ
Paul L. G. Vlek
Received: 25 May 2005 / Accepted: 24 April 2006
Springer Science+Business Media B.V. 2006
Abstract This paper evaluates the potential of
nine multipurpose tree species for afforestation of
degraded land in the Khorezm region, Central
Asia, particularly their suitability for biodrainage
i.e., lowering the elevated groundwater table
through the transpirative capacity of plantations.
For this purpose water use (WU), water use efficiency (WUE) and tree physiological factors
influencing transpiration were assessed during two
consecutive years. Mean daily leaf transpiration
differed significantly among the species and ranged during the seasons from 4.5–5.2 mmol m–2 s–1
for Prunus armeniaca L. to 4.5–10 mmol–2 s–1 for
Elaeagnus angustifolia L. WU differences were
triggered by species physiological features such as
capability of water uptake by roots. Transpiration
rates and the length of fine roots correlated highly
(r = 0.7). Correlations of leaf transpiration rates
with leaf area were weaker (r = 0.6). No correlations were found between salt content in plants
and water uptake under conditions of slight-tomoderate rootzone soil salinity. Values of WUE
per root and shoot DM were similar averaging,
respectively, 0.2 and 0.3 g DM g–1 water for twoyear-old trees, and decreased with age. In addition
to WU characteristics, also salinity tolerance,
growth rate and the ability to produce fodder and
fuelwood must be considered during species
selection. Regarding these features, the N-fixing
E. angustifolia ranked the highest, combining high
WU, fast growth and production of nutritious
feed. Examined Populus spp. and Ulmus pumila
L. ranked lower but still represented potential
candidates for biodrainage purposes. Typical fruit
species in the region such as P. armeniaca and
Morus alba, showed low biodrainage potential.
A. Khamzina (&) Æ J. P. A. Lamers Æ C. Martius Æ
P. L. G. Vlek
Department of Ecology and Resource Management,
Center for Development Research, Walter Flex Str.,
3, Bonn 53113, Germany
e-mail: [email protected]
Introduction
M. Worbes
Institute of Agronomy in the Tropics, University of
Goettingen, Grisebachstrasse 6, Goettingen 37077,
Germany
Keywords Biodrainage Æ Root growth Æ
Transpiration per unit leaf area Æ Water use
efficiency
High groundwater table (GWT) and salinity levels
are the conditions prevailing in many irrigated
landscapes of the Aral Sea Basin (Ibrakhimov et al.
2004; Martius et al. 2004). Khorezm region, an
administrative district in the Republic of Uzbekistan, located at the southern edge of the Aral Sea
Basin, is an oasis of irrigated farmland. Khorezm’s
123
Agroforest Syst
landscape is characterized by insignificant slopes,
low hydraulic conductivity in the upper soil horizons, and extremely slow lateral groundwater flows
(Katz 1976; Mukhammadiev 1982). These adverse
natural drainage conditions, aggravated by excessive irrigation and poorly maintained drainage
systems, have resulted in the elevated GWT (Ibrakhimov et al. 2004). The evaporation of the
shallow saline GWTs has caused secondary soil
salinization throughout the entire irrigated area of
Khorezm (Martius et al. 2004).
Biological drainage uses the transpirative
capacity of vegetation and especially trees, to cope
with elevated GWTs in the landscape by enhancing their discharge or/and reducing their recharge.
Since conventional drainage systems require
expensive capital investments for installation,
operation and maintenance, the implementation
of biodrainage may represent a cost effective
addition or even alternative (Heuperman et al.
2002). Extensive Australian research (e.g., Heuperman et al. 2002) concluded that the biodrainage plantations in the GWT discharge areas,
which are e.g. prevailing in Khorezm, would not
be effective on a regional scale. However, even the
localized impact of biodrainage plantations is
important for improvement of the degraded patches of land which are abandoned from agricultural activities and, being dispersed throughout
Khorezm, currently constitute about 20% of the
irrigated area in the region (Martius et al. 2004).
Designing efficient biodrainage plantations to
enhance the discharge of shallow and saline GWTs
involves a careful selection of suitable tree species
with preference to those having a high transpiration
capability (Heuperman et al. 2002). The in-depth
overview on biodrainage by Heuperman et al.
(2002) emphasized the need to include, in addition
to water use (WU) other criteria for tree selection
such as salinity tolerance and, in particular, rooting
characteristics. Among the latter, deep rooting,
significant horizontal root system extension and
increased root density indicated suitability for
biodrainage purposes. Moreover, Heuperman
et al. (2002) advocated the inclusion of site-specific
characteristics thus stressing the need for field
studies under natural conditions.
The assumption that WU per unit leaf area
(LA) differs among tree species has been debated
123
for a long time. Given the lack of evidence that
stomata behavior is different among tree species
even in conditions of water scarcity, Landsberg
(1999a) concluded that water use per unit LA, is
not an appropriate indicator for the choice of
species. In contrast, Deans and Munro (2004)
examined WU of dry land trees such as Acacia
seyal Del and Acacia aneura F. Muell ex Benth
and revealed significant differences in leaf transpiration rates among species. Existing knowledge on tree WU in Uzbekistan is insufficient
since transpiration rates of various locally grown
tree species were estimated (e.g., Botman 1988;
Mikhailova 1986) solely by using destructive
gravimetric methods measuring weight differences over periods of 3 min (Ivanov et al. 1950).
To test the hypothesis whether transpiration
rates per unit LA are the same irrespective of tree
species, the present study examined the characteristics of nine native and introduced tree species
under the agro-ecological conditions of the Aral
Sea region, using Khorezm as a model region. An
effort was made to identify those species which
combined a high WU with salinity tolerance and
an ability to rapidly produce high quality fodder
and fuelwood (Khamzina et al. 2006), as this may
increase farmers’ willingness for adopting the
low-cost biodrainage technology.
Materials and methods
Description of the study sites
The research was conducted at the Khiva Research Station of the Uzbek Forestry Research
Institute located at 4141¢ N latitude, 3940¢ E
longitude and at an altitude of 113 m. The study
region is characterized by an arid, strongly continental climate with high irradiance and sparse
precipitation. Average annual precipitation between 1990 and 2002 amounted to 101 mm and
was exceeded by precipitation for the study years
2002 and 2003 by 75% and 70%, respectively.
Figure 1 depicts the experienced atmospheric
parameters that govern the loss of water via leaf
transpiration.
Experimental plantations were established at
two sites which measured 0.14 ha each and were
Agroforest Syst
b) middle (16 MaP)
50
40
1200
30
800
20
400
10
1200
30
800
20
400
0
d) end (7 MaP)
2000
60
50
1600
50
40
1200
30
800
20
400
10
0
0
9-10 11-12 13-14 15-16 17-18 19-20
Time, h
2000
1600
40
1200
30
800
20
PFD, µmol m-2 s-1
60
PFD, µmol m-2 s-1
T, °C & RH, %
40
0
c) end (18 MaP)
7-8
1600
50
10
0
0
2000
60
1600
T, °C & RH, %
T, °C & RH, %
60
70
T, °C & RH, %
AT
RH
PFD
2000
PFD, µmol m-2 s-1
70
PFD, µmol m-2 s-1
a) beginning (14 MaP)
400
10
0
0
7-8
9-10 11-12 13-14 15-16 17-18
Time, h
Fig. 1 Air temperature (T), relative humidity (RH) and photon flux density (PFD) in the beginning (14 months after
planting (MaP)), middle (16 MaP) and the end (7 and 18 MaP) of the growing seasons 2003–2004
located 500 m apart from each other. Soil profiles
represented two major soil textures in Khorezm:
(i) a light sandy soil underlain by a loam layer
from 75 cm downwards (hereafter referred to as
the sandy site) and (ii) a more finely textured silt
loam underlain by a loam layer from 85 cm
downwards (loamy site). The available water
content estimated as the difference between soil
moisture at the field capacity and at the wilting
point, determined by the pressure membrane
method, averaged to 89 and 49 mm m–1 within
the examined profiles at the loamy site and sandy
site, respectively. Both sites were leveled and
leached from salts in the beginning of the study
period, which provided homogeneity of initial
growing conditions. More details on soil properties and methods for soil analysis are reported in
Khamzina et al. (2006).
Due to adequate availability of irrigation water
in the region during the study years, the presence
of intensively irrigated rice fields in the vicinity,
and a high GWT, the trees at the loamy site only
needed occasional irrigation. At the sandy site,
where the soil moisture remained close to field
capacity, only one irrigation event was necessary
at the onset of each growing season. For the rest
of the time the trees relied on groundwater and
precipitation.
The GWT at the sandy site was in the range of
0.7–1.3 m during the growing period, whereas at
the loamy site it ranged from 1.0 to 1.3 m. Thus,
the average GWT depth monitored at the sites
was equal or less than the long-term mean of
1.22 m for the region ((Ibrakhimov et al. 2004);
only those months observed in the sites were used
for comparison). The GWT dropped during the
winter and rose again with the start of spring
leaching in the surrounding agricultural fields.
During both observation years mean electrical
conductivity (EC) of GWT was highest at the
123
Agroforest Syst
non-irrigated sandy site (4.3 dS m–1 vs. 3.3 dS m–1
at the loamy site). Both exceeded the long-term
mean salinity of 1.8 g l–1 (Ibrakhimov et al. 2004).
Experimental design
The experiment was laid out in a randomized
incomplete block design with six replications.
Plots consisted of two rows with 25–30 trees,
spaced 1 m · 3.5 m. This spacing was introduced
to minimize potential root competition between
neighboring trees and to avoid mutual shading
during the experiment.
The pre-selected ten deciduous species represented a variety of life spans and tolerances to
drought and salt stress: apricot tree (Prunus
armeniaca L.), black poplar (Populus nigra var.
pyramidalis (Rozan) Spach), black willow (Salix
nigra Marshall), Eastern catalpa (Catalpa bignonioides Walter), Euphrates poplar (Populus euphratica Oliv.), Russian olive (Elaeagnus
angustifolia L.), salt cedar (Tamarix androssowii
Litv.), Siberian elm (Ulmus pumila L.), swamp
ash (Fraxinus pennsylvanica Marshall), and white
mulberry (Morus alba L.). Seeds of all species
were collected from plantations on the station,
germinated and grown for one year in a tree
nursery located 7.2 km from the experimental
fields. After 12 months, in total 50 saplings of
each species were transplanted into the experimental plots. At each site, the tree species were
completely randomized within the experimental
plots.
Transpiration rates and leaf area
Leaf transpiration rates of eight trees per species
were measured with a steady state porometer
(Li-cor 1600). Concurrently, the porometer sensors measured irradiance (photon flux density),
air temperature and relative humidity. The first
porometer surveys occurred 7 months after
transplanting the saplings from the nursery into
the experimental plots (MaP). This corresponded
with the end of the first growing season, when the
leaf area became sufficiently large to fit the narrow leaf aperture cap. Subsequent measurements
were conducted three times during the second
growing season each time for five consecutive
123
days: shortly after the leaves flushed, in the
mid-season and at the end of the season, which
corresponded to 14, 16, and 18 MaP. At each
tree, the abaxial side of three-to-four sunlit leaves
was measured every 2 h during 13 hours of
sunshine duration. The fine and scaly leaves of
T. androssowii were unsuitable for measurements
with the available aperture cap. Also, P. euphratica
at the loamy site developed very narrow leaves
inappropriate for the aperture cap. Finally, due to
time and equipment limitations, during the second
growing season at the sandy site only three species
could be measured at 14, 16, and 18 MaP. These
had shown high growth and utility potential at
7 MaP.
At 7 and 19 MaP (the end of the two growing
seasons in 2002–2003) the observed trees were
completely defoliated and fresh leaf mass determined. Leaf sub-samples were transported in a
cool-box to the laboratory to determine total oneside LA in two replicates with a leaf area meter
(Li-cor 1200). Daily transpiration of the whole
canopy was estimated using total LA of the
measured trees and assuming no self-shading
within canopies. Water use efficiency (WUE) of
trees was calculated as the estimated canopy
transpiration with relation to below- and aboveground dry matter (DM) production according to
Larcher (1995, pp. 121 ff).
Biomass
At 7 and 19 MaP, 3–4 trees per species and plot
were cut at ground level and separated into stem,
branch and foliage. P. euphratica was not
harvested at 7 MaP at the loamy site due to low
survival rate. Complete tree root systems were
manually excavated to quantify belowground
biomass and rooting extent. Maximal rooting
depth and maximal radial extension of the root
system were determined with a measuring tape. In
the laboratory, roots were washed free of soil and
separated into coarse (Ø >3 mm) and fine roots
(Ø < 3 mm). Coarse root length was measured
with a measuring tape. The length of live fine roots
was determined using the modified Newman lineintersect method (Tennant 1975). All above- and
below-ground fractions were dried to constant
weight at 103C to determine DM. The relative
Agroforest Syst
relationship of the above- and below-ground DM
was expressed as root/shoot ratio (RSR).
Chemical analysis
The concentration of salts in plant tissues, particularly leaves, provides information about salt
accumulation ability and salt tolerance of plants
(Heuperman et al. 2002). Therefore, dried samples from leaves, twigs, stems, coarse, and fine
roots were collected at 19 MaP when the accumulated salt content in plant tissues was expected
to be the highest. The samples were selected from
trees with a leaf mass judged representative for
each species and soil type, ground and analyzed
for contents of chloride (Cl–) and sulphate (SO2–
4 ),
the dominating soil salt anions in the region.
Concentration of salts in soil solution and tissues
was determined on a 1:5 water extract. Chloride
content was measured titrametrically. Sulphate
concentration was determined by precipitation
with 10% BaCl2.
species and soil type and their interactions were
compared at p < 0.05 level of significance. Individual treatment means were compared with the
Tukey Post Hoc test where the ANOVA test had
indicated significant effects. All statistics were
carried out with SPSS 11.0 software.
Results
Aboveground biomass
The GWT was monitored using four observation
wells (Ø = 4 cm) installed down to a depth of 1.8–
2.2 m. The wells were polyethylene pipes closed
at the bottom, perforated and protected from
clogging with a fine synthetic filter. The EC of the
groundwater was measured every 10 days as well
as immediately before and after each irrigation
event.
At two locations at each site, in the beginning
and end of each growing season soils were sampled in two replicates every 0.2 m horizons down
to the GWT for the analysis of salt contents.
The total DM production at 7 MaP was in general
higher for all tree species at the sandy site, but at
19 MaP some trees at the loamy site had gained
higher total DM. The utilizable (leaves and wood)
aboveground DM at 7 MaP was also higher at the
sandy site but at 19 MaP for a number of species
this did not differ significantly between the two
sites. The RSRs were consistently higher at
7 MaP than at 19 MaP especially for the sandy
soil, but this soil-specific difference disappeared
for most species at 19 MaP (Fig. 2 and Table 1).
With regards to total DM production E. angustifolia, P. nigra var. pyramidalis and U. pumila,
always ranked in the upper quartiles irrespective
of soil type and harvest date. P. euphratica,
though a good performer at the sandy site, was
hardly productive in the loamy soil. S. nigra and
M. alba, however, had a higher total DM production at 19 MaP at the loamy site and ranked in
the upper quartiles. Whereas growth of a
species such as U. pumila was shifted towards the
belowground DM, other species such as
E. angustifolia, invested relatively more in the
aboveground DM, as suggested by its lower RSR
(Fig. 2 and Table 2).
Statistical analyses
Root growth parameters
All data were checked for normality and normalized using the logarithmic transformation
when necessary. Analysis of variance (ANOVA)
was performed using the General Linear Model
procedure. With bivariate Pearson correlations
the relations were tested between mean daily
transpiration rate and environmental and physiological parameters measured at 7 and 19 MaP.
The effect of the treatment variables such as tree
The ANOVA revealed a highly significant influence of species, soil type and harvest date on virtually all root growth parameters (Tables 1 and 2).
At 7 MaP the DM and, for the most part, total
lengths of the fine roots were greatest for species
at the sandy site (Fig. 3 and Table 1). The light
soil texture and higher GWT apparently enhanced fine root growth. At 19 MaP these trends
were maintained, although some species such as
Groundwater and soil sampling
123
Agroforest Syst
a) 7 MaP
Coarse roots
Stem
Leaves
0.6
Table 1 Standard errors of the differences between means
according to harvest dates (MaP) and soil types
Fine roots
Twigs
Root/shoot ratio
2.0
Factor/parameter
1.2
0.3
0.8
0.2
sandy
FP
MA
CB
PA
SN
UP
EA
PN
FP
MA
CB
PA
0.0
PE
0.0
SN
0.4
EA
0.1
Root/shoot ratio
1.6
0.4
PN
UP
Biom ass, kg tree -1
0.5
loamy
b) 19 MaP
5
1.2
2
0.8
0.4
0
0
sandy
loamy
Fig. 2 Dry matter production of nine tree species and
root/shoot ratio according to the soil type at 7 months after
planting (2a: 7 MaP) and 19 MaP (2b). Connecting lines of
RSR are to aid in viewing trends only. Species are ranked
in descending order according to the total biomass in sandy
soil. CB = C. bignonioides, EA = E. angustifolia, FP = F.
pennsylvanica, MA = M. alba, PA = P. armeniaca,
PE = P. euphratica, PN = P. nigra var. pyramidalis,
SN = S. nigra, UP = U. pumila
P. armeniaca and C. bignonioides did not perform
significantly worse at the loamy site. An exception
occurred with fine root DM of M. alba, which was
almost by 50% greater in the loamy than in the
sandy soil at 19 MaP.
Growth response of structural roots to the soil
texture was not uniform. With age, M. alba,
S. nigra and P. armeniaca developed considerably
greater coarse root DM in loamy soil (Fig. 2).
However, the length of coarse roots of these
species did not differ significantly with soil type
(Fig. 3 and Table 1). The other tree species
developed higher structural root mass and length
in sandy soil.
Shallow GWT at both sites prevented root
development below the capillary fringe. Even a
123
92.8***
19.1***
2.8***
18.1***
36.8***
21.2***
0.1**
127.8***
176.5***
4.8ns
10.2***
75.3*
42.1***
4.1***
–
–
Soil
97.1ns
20.1ns
2.6***
18.9ns
36.4ns
21.6ns
0.1*
133.1ns
202.6**
4.3ns
9.3***
84.8ns
48.3ns
5.1ns
–
–
Soil
7 MaP
19 MaP
26.3*
9.2*
1.8***
4.8ns
8.0ns
4.9ns
0.1*
31.3ns
33.7ns
5.8ns
6.8***
170.7ns
94.4ns
0.5ns
–
294.9ns
58.1ns
7.2**
59.0ns
119. 3ns
68.3ns
0.1ns
376.1*
491.7***
2.4***
24.7***
7.1ns
11.8ns
7.3**
0.2*
–
0.8ns
*, **, *** respectively indicate significance levels < 0.05,
< 0.01 and < 0.01; ns = not significant
EA
PE
PN
UP
SN
FP
MA
CB
PA
1
Root/shoot ratio
1.6
3
EA
PE
PN
UP
SN
FP
MA
CB
PA
Biom ass, kg tree -1
2
4
Total DM
Coarse root DM
Fine root DM
Stem DM
Twig DM
Leaf DM
Root/shoot ratio
Coarse root length
Fine root length
Maximal depth
Maximal radius
WUE per root DM
WUE per shoot DM
Tree transpiration
SO–2
4 content in
all fractions
Cl– content in
all fractions
MaP
species such as U. pumila, which is genetically
predisposed to develop deeply penetrating
taproots (Forestry Compendium 2000), had no
prominent primary root, but instead a rather
dense and superficial lateral root system. Trees at
the loamy site rooted in general more deeply at
19 MaP, due to the lower GWT (Fig. 3 and
Table 1).
The radial extension of coarse roots in sandy
soil varied according to species and was considerable, particularly for both Populus spp. At the
loamy site, the horizontal spread of the coarse
roots was less significant but varied according to
species at 7 MaP, with P. nigra var.pyramidalis
exploiting the largest radius (Fig. 3 and Table 2).
Among the examined root parameters, fine
root length was highly and positively correlated
with transpiration rates of the trees (Table 3).
Although maximal rooting depth was not consistently different among the species, increased
transpiration rates were correlated with the vertical expansion of the root systems. Tree species
with considerable horizontal extension exhibited
rather low root length densities (RLD), and
therefore correlations between transpiration rate
and RLD were poor and in most cases even
Agroforest Syst
Table 2 Differences between species means as presented in Figs. 2 and 3
Parameter
p
Sandy soil
Loamy soil
CB EA FP MA PA PE PN SN UP CB EA FP MA PA PE PN SN UP
7 MaP
Total DM
Coarse root DM
Fine root DM
Wood DM
Leaf DM
Root/shoot ratio
Coarse root length
Fine root length
Maximal depth
Maximal radius
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
0.150
0.032
< 0.001
< 0.001
< 0.001
abc
abc
ab
a
ab
a
a
abc
a
ab
d
c
bc
d
c
a
a
bc
a
ab
abc
abc
bc
ab
ab
a
a
c
a
ab
ab
ab
ab
a
a
a
a
ab
a
ab
a
a
a
a
a
a
a
a
a
a
cd
bc
ab
bcd
bc
a
a
abc
a
b
bcd
abc
ab
cd
ab
a
a
abc
a
ab
abc
abc
ab
abc
ab
a
a
abc
a
ab
abc
abc
c
abc
a
a
a
bc
a
ab
ab
a
abc
a
ab
abc
ab
ab
b
ab
bc
ab
bc
bc
bc
a
b
ab
b
ab
ab
a
bc
ab
ab
c
b
ab
ab
ab
ab
a
bc
a
ab
abc
ab
ab
b
ab
a
a
a
a
a
ab
a
a
a
a
–
–
–
–
–
–
–
–
–
–
c
b
bc
c
c
ab
b
b
b
b
ab
a
ab
ab
ab
abc
ab
ab
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ab
ab
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c
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bc
b
b
b
ab
19 MaP
Total DM
Coarse root DM
Fine root DM
Wood DM
Leaf DM
Root/shoot ratio
Coarse root length
Fine root length
Maximal depth
Maximal radius
< 0.001
0.001
0.002
< 0.001
< 0.001
0.025
< 0.001
0.076
0.085
0.014
a
a
a
a
a
bcd
a
ab
a
a
b
c
ab
b
c
a
b
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a
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a
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d
ab
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a
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a
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a
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a
a
a
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a
a
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a
a
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ab
b
a
a
a
a
a
a
a
a
a
abc
a
a
a
a
a
a
a
a
a
a
a
a
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a
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a
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a
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a
a
The same superscripts within the columns indicate that the means are not significantly different at p < 0.05. The species
names are spelled out in Figs. 2 and 3
negative. Correlation coefficients between transpiration and total tree LA were mostly high
but did not indicate a consistent correlation
(Table 3).
Despite differences in species performance
with respect to soil type, harvest date and
parameter measured, species such as E. angustifolia, both Populus spp. and U. pumila were
found in the upper quartiles for virtually all
rankings. Among these, P. euphratica was the
leading species at the sandy site but showed slow
root elongation and low DM production at the
loamy site. On the other side of the spectrum
after all rankings was P. armeniaca, which always
had the lowest belowground DM irrespective of
the tested parameters and soil type (Table 2).
Transpiration
The diurnal transpiration courses of most species
showed one daily peak at different points during
the day depending on the period in the season
(Fig. 4). At 14 MaP the highest values recorded
at the loamy site happened between 11:00 and
12:00 h. At 16 and 18 MaP water loss values at
the loamy site peaked between 13:00 and 14:00 h
and for U. pumila, M. alba and S. nigra additionally between 17:00 and 19:00. These three
species decreased their transpiration during the
hottest time of the day. At the sandy site, during
the early, mid and late season, all species peaked
at 11:00 and 12:00 h, and at the end of the season
a second peak was observed between 15:00 and
16:00 h.
The transpiration rates per unit LA were much
higher at 18 MaP than at the end of the previous
season (Table 4). Mean values of leaf transpiration followed the sequence 16 MaP (mid growing
season) 18 MaP (late season) > 14 MaP (early
season) > 7 MaP (end of the first season), which
was consistent with the mean air temperature and
relative humidity during these periods. On the
other hand, this sequence did not correspond with
the irradiance given by in average higher values
of photon flux density (PFD) observed at the end
of both growing seasons.
123
Agroforest Syst
Fine root length
Coarse root length
Ground water table
Maximal rooting depth
Maximal rooting radius*10
16
14
0.0
0.2
12
0.6
8
0.8
6
Depth, m
0.4
10
1.0
4
1.2
0
1.4
EA
CB
UP
PN
FP
SN
MA
PA
2
EA
CB
UP
PN
PE
FP
SN
MA
PA
Root le ngth and ra dial e xte ns ion, m
a) 7 MaP
sandy
loamy
120
0.0
100
0.2
0.6
60
0.8
40
Depth, m
0.4
80
1.0
1.2
0
1.4
EA
PN
PE
UP
FP
SN
MA
CB
PA
20
EA
PN
PE
UP
FP
SN
MA
CB
PA
Root le ngth and ra dial e xte ns ion, m
b) 19 MaP
sandy
loamy
Fig. 3 Length of coarse and fine roots, maximal radius and
depth of root systems of nine tree species, and GWT depth
according to soil types and harvest dates. Values of max
radius are multiplied by 10 for improved visualization.
Connecting lines of max radius and depth are to aid in
viewing trends only. Species are ranked in descending
order according to the total length in sandy soil. CB = C.
bignonioides, EA = E. angustifolia, FP = F. pennsylvanica,
MA = M. alba, PA = P. armeniaca, PE = P. euphratica,
PN = P. nigra var.pyramidalis, SN = S. nigra, UP = U.
pumila
ANOVA revealed a significant effect of
species on mean transpiration rate per unit LA at
the loamy site (Table 4). At the sandy site, where
only three the best performing species could be
measured during the second growing season,
species-related differences were found only at the
onset of the season with E. angustifolia transpiring significantly more water. Transpiration of
trees grown in the loamy soil was significantly
higher than that of trees at the sandy site but at 7
and 16 MaP only. Overall, the highest water
consumption per unit LA was shown by E. angustifolia, U. pumila and P. euphratica at 18 MaP
whereas P. armeniaca was the least transpiring
species during this period of the season.
Water use efficiency
WUE in physiological studies is usually measured
as the ratio of photosynthetic to transpiration
rate, but for ecological, agricultural, and forestry
purposes the relation of DM production to water
consumption is considered more informative
(Larcher 1995, pp. 121 ff; Landsberg 1999b).
The WUE was calculated separately for above(WUEa) and belowground (WUEb) DM
production. Overall WUE varied considerably
between species at 19 MaP. In particular, the
WUE values of P. armeniaca at the sandy site and
of F. pennsylvanica at the loamy site at 7 MaP by
far exceeded those of the other species, whereas
this trend was not maintained at 19 MaP. The
values of WUE per unit root DM production
Table 3 Pearson correlation coefficients for mean daily transpiration rate, leaf area, fine root DM, coarse root DM, fine
root length, coarse root length, maximal radius and maximal depth of root systems, root/shoot ratio, and root length density
Species (N of cases)
Leaf
area
Coarse Fine
Root/shoot Coarse
Fine
Maximal Maximal Root length
root DM root DM ratio
root length root length depth
radius
density
C. bignonioides (5)
0.87 0.52
E. angustifolia (11)
0.80* 0.69*
F. pennsylvanica (8)
0.54 0.52
M. alba (7)
0.61 0.65
P. euphratica (6)
0.71 0.58
P. nigra var. pyramidalis (5) 0.88 0.91*
P. armeniaca (6)
0.91* 0.82*
S. nigra (4)
–
0.91
U. pumila (12)
0.78* 0.73**
Overall
0.60** 0.62**
0.02
0.53
0.05
0.44
0.81
0.50
0.59
0.68
0.62*
0.61**
–0.71
–0.82**
–0.48
–0.89**
–0.90*
–0.91*
–0.45
0.55
–0.76**
–0.54**
0.77
0.59
0.46
0.53
0.58
1.00**
0.43
0.91
0.34
0.51**
0.90*
0.60
0.85**
0.84*
0.81
0.96*
0.56
1.00*
0.66*
0.70**
0.93*
0.59
0.92**
0.85*
–0.42
0.93*
0.85*
0.98*
–0.40
0.21
*, **, *** indicate correlations respectively significant at 0.05, 0.01 and < 0.01 level (2 tailed)
Numbers in bold indicate significant correlations
123
0.03
0.58
0.61
0.32
0.72
0.52
0.86*
0.51
0.64*
0.51**
0.18
–0.57
–0.95**
0.62
–0.49
–0.66
–0.44
0.71
–0.61*
–0.21
-2
Transpiration, mmol m s
-1
Agroforest Syst
16
14
12
14 MaP (early season)
16 MaP (mid season)
18 MaP (late season)
a) Sandy soil
10
8
6
4
E.angustifolia
2
M.alba
P.euphratica
0
-2
Transpiration, mmol m s-1
16
P.nigra
P.armeniaca
b) Loamy soil
14
S.nigra
U.pumila
12
10
8
6
4
2
0
7-9
9-10
11-12 13-14 15-16 17-18 19-20
Time, hrs
7-9
9-10
11-12
13-14
15-16
17-18
19-20
7-9
9-10
11-12
13-14
15-16
17-18
19-20
Time, hrs
Time, hrs
Fig. 4 Diurnal variations of leaf transpiration rates at the beginning (14 MaP), middle (16 MaP) and end (18 MaP) of the
growing season according to tree species and soil type
Table 4 Mean daily leaf transpiration rates (mmol m–2 s–1) at the beginning (14 MaP), middle (16 MaP) and end (7 and
18 MaP) of the growing seasons according to tree species and soil type
Species (N of cases)
7 MaP
Sandy site
C. bignonioides (42)
E. angustifolia (53)
F. pennsylvanica (48)
M. alba (52)
P. armeniaca (48)
P. euphratica (48)
P. nigra var. pyramidalis (44)
S. nigra (44)
U. pumila (52)
2.11a
2.11a
2.46a
2.22a
2.20a
2.22a
2.43a
2.30a
2.28a
–
4.51b
–
–
–
3.30a
–
–
3.30a
–
5.12a
–
–
–
4.82a
–
–
4.53a
–
9.99a
–
–
–
8.32a
–
–
9.22a
Loamy site
C. bignonioides (106)
E. angustifolia (171)
F. pennsylvanica (118)
M. alba (108)
P. armeniaca(69)
P. nigra var. pyramidalis (99)
S. nigra (115)
U. pumila (150)
2.12a
2.68b
2.36ab
2.79b
2.40ab
2.50ab
2.40ab
2.62b
–
4.37b
–
2.64a
–
–
–
3.63b
4.38ab
9.12c
7.13bc
6.51ab
5.15ab
2.99a
7.31bc
7.38bc
6.69ab
9.39b
7.86ab
7.46ab
4.48a
6.04ab
5.70ab
9.49b
Analysis of variance, probability > F (=alpha)
Soil
0.002
Species
0.239
Species*soil
0.079
0.699
< 0.001
0.323
< 0.001
< 0.001
0.266
0.773
< 0.001
0.436
Across harvest dates
MaP
Soil
Species
Soil*species
14 MaP
16 MaP
18 MaP
< 0.001
< 0.001
< 0.001
< 0.001
Means with the same superscript within the column are not significantly different at p < 0.05
123
Agroforest Syst
were higher than those per unit aboveground
DM production in both species. At 19 MaP,
P. armeniaca and S. nigra were the best performers regarding WUEa, and F. pennsylvanica
was the most efficient species regarding WUEb
(Fig. 5).
WUE significantly decreased with tree age
(Table 1): the most for F. pennsylvanica, the least
for E. angustifolia and P. nigra var. pyramidalis.
A general trend at 7 MaP was that WUE was
inversely related to daily canopy transpiration. At
19 MaP, this trend was not observed (Fig. 5).
WUE per root DM
WUE per shoot DM
Transpiration
WUE, m g DM g-1 water
1600
5
1400
4
1200
1000
3
800
2
600
400
1
200
Transpiration, l d -1 tree -1
a) 7 MaP
0
0
A E P P B N A
PAM P F U C P E
sandy
PA MA FP UP CB PN EA
loamy
b) 19 MaP
Salt accumulation in plant tissues
Average soil salinity within the top 1 m layer,
determined by a sum of potentially toxic ions
(Kovda et al. 1985) was classified as slight-tomoderate. At both sites, the prevailing salinity
type was defined as sulphate-chloride. The soils at
the sandy site had significantly higher sulphate
salt contents than those at the loamy site (Table 5). The EC of the GWT was also higher at the
sandy site.
Consequently, the content of SO2–
4 was higher
in plant tissues of trees grown on the sandy soil
when compared to those on the loamy soil (Fig. 6
and Table 1). In contrast, Cl– content did not
differ according to the soil type. The mineral
content varied depending on species but particularly the Cl– content at the sandy site did not
differ significantly between species. Salt concentrations highly depended upon the plant fraction
(p < 0.001). In line with previous observations that
responses to soil salinity occur first in the shoot,
despite the root being exposed to the soil salinity
(Poljakoff-Mayber and Lerner 1999), the highest
Cl– concentrations were found in leaves and fine
root fractions rather than in the perennial parts,
whereas SO2–
4 was mostly concentrated in tree
leaves and stems.
WUE, m g DM g-1 water
60
160
50
120
40
30
80
20
40
10
Transpiration, l d -1 tree -1
200
0
0
UP EA PE
sandy
UP EA PA SN PN FP MA CB
loamy
Fig. 5 Water use efficiency per root and shoot dry matter
(WUE) and daily tree transpiration of nine tree species
according to soil types and harvest dates. Species are
ranked in descending order according to the total WUE in
sandy soil. Species effect is significant for WUE per shoot
and root DM (p < 0.01) at 19 MaP only and for transpiration both at 7 MaP (p < 0.001) and 19 MaP (p < 0.01).
CB = C. bignonioides, EA = E. angustifolia, FP = F.
pennsylvanica, MA = M. alba, PA = P. armeniaca,
PE = P. euphratica, PN = P. nigra var. pyramidalis,
SN = S. nigra, UP = U. pumila
123
Table 5 Concentration of Na+, Cl– and SO–2
ions
4
(cmol kg–1) in 1 m soil layer in the beginning and end of
the growing seasons
Sampling date
Na+
Cl–
SO–2
4
Sandy site
1 MaP
7 MaP
13 MaP
19 MaP
0.6a
1.1a
1.1a
1.0a
0.4a
0.8a
0.7a
0.5a
1.6a
1.9a
2.0a
2.4a
Loamy site
1 MaP
7 MaP
13 MaP
19 MaP
0.7a
1.3b
1.1ab
0.9ab
0.4a
0.7b
0.7b
0.5ab
0.8a
1.7b
1.3ab
0.9a
0.01
0.816
0.996
0.031
0.06
0.749
ANOVA, probability > F (=alpha)
MaP
0.687
Soil
0.632
MaP*Soil
0.417
Means with the same superscript within the column are not
significantly different at p < 0.05
Agroforest Syst
The sulphate content in tissues of all tree species
was significantly lower than that of the halophytic
shrub T. androssowii which is known for its ability
to accumulate salts (Forestry Compendium 2000).
The chloride content in C. bignonioides, U. pumila
and especially F. pennsylvanica at the sandy site
was relatively high and was comparable with that
in T. androssowii (Fig. 6).
Transpiration rates did not appear to correlate
with concentration of the examined salts in the
plant tissues measured at the end of the growing
season 2003.
Discussion
Loamy_leaves
Sandy_leaves
Loamy_all
Sandy_all
7.5
5
4
6
3
4.5
2
3
1.5
1
0
0
3
1
2.5
0.8
2
0.6
1.5
0.4
1
0.2
0.5
0
SO4- 2 in all fra ctions, g 10 0 g- 1 D M
9
Cl- in all fra ctions , g 10 0 g- 1 DM
Cl- in leaves, g 100 g -1 DM
SO4-2 in leaves, g 100g -1 DM
The choice of tree species is crucial when considering trees as a means to enhance discharge of
0
PA CB EA FP MA PE PN SN UP TA
Species
Fig. 6 Mean sulphate and chloride content in leaves and
that averaged over all plant fractions (leaves, twigs, stems,
fine and coarse roots) for nine tree species at 19 MaP
according to the soil type. Species are ranked in ascending
order according to sulphate content in leaves at the sandy
site. Species and soil effects are significant for sulphate
content (p < 0.001 and p < 0.01, respectively). CB = C.
bignonioides, EA = E. angustifolia, FP = F. pennsylvanica,
MA = M. alba, PA = P. armeniaca, PE = P. euphratica,
PN = P. nigra var. pyramidalis, SN = S. nigra, UP = U.
pumila, TA = T. androssowii
the shallow and saline GWTs within degraded
patches of irrigated land in the Aral Sea Basin.
The ideal multipurpose species should combine a
number of features such as high survival rates,
quick growth, halophytic and xerophytic characteristics, and high utility value of firewood or foliage (Khamzina et al. 2006) since financial
returns are key to farmers (Landsberg 1999a). For
biodrainage purposes, additional characteristics
such as WU and salinity tolerance should be included as selection criteria. We have examined
such parameters of nine deciduous tree species
and attempted to correlate WU of the trees with
the internal factors, determined by physiological
features of the tree species, and the environmental parameters.
Influence of environmental factors on the
transpiration
As the soil moisture conditions were maintained
at an adequate level during the experiment, we
assume that water uptake by roots met the
requirements of potential evapotranspiration
imposed by atmospheric factors.
The dependency of transpiration on various
atmospheric variables makes it difficult to find a
clear relationship on a single one of these (Angelocci et al. 2004). This was also experienced
in this study, given the consistent—but not
high—dependency of transpiration rates over all
species on air temperature (r = 0.57), relative
humidity (r = 0.47) and irradiance (r = 0.47).
These relationships improved when differentiated
according to species, since the tree-specific physiological features (such as ability to regulate stomata opening) together with environmental
factors altered the transpiration rates. Diurnal
transpiration curves showed unrestricted water
loss of some species such as E. angustifolia, while
M. alba, S. nigra and U. pumila were more sensitive to high temperature and irradiance and
demonstrated a reduced transpiration during the
hottest time of the day, which decreased the mean
daily transpiration by these species.
Presence of salts in soil and water can significantly reduce WU of plants (Poljakoff-Mayber
and Lerner 1999), which, for the hydromorphic
salt-affected soils in Khorezm makes salt
123
Agroforest Syst
tolerance an important criterion for species
selection. The level of soil salinity experienced at
the experimental sites, however, did not affect the
growth and transpiration of most of the examined
species, which were able to expel salts from the
‘‘single phase water uptake’’ (Heuperman et al.
2002). This may explain the low correlation between leaf transpiration rates and concentrations
of predominant salts accumulated in the tissues
and generally the low salt concentration in tissues
of the tree species in comparison with halophytic
T. androssowii.
However, the sandy site had higher values of
groundwater EC than the loamy site which
clearly affected P. armeniaca, C. bignonioides,
F. pennsylvanica and M. alba—all species that
previously were reported as being salt sensitive
(Fimkin 1983). The transpiration of these species
could not be measured at the sandy site in the
second season but the observed visual signs of
stress (leaf chlorosis and necrosis) correspond
with lower transpiration rates. On the other
hand, high transpiration rates of E. angustifolia
and U. pumila at the sandy site fall in the range
of their transpiration values at the loamy site,
showing that these species were rather insensitive
to the present degree of groundwater and soil
salinity.
Influence of tree physiological factors on
transpiration
The high correlations found between the transpiration rates per unit LA and root system
characteristics and morphology are in line with
other findings. Bi et al. (1992) studied the competitive advantages of young Eucalyptus trees and
pointed out the importance of measuring the
RLD. So did Nnyamah and Black (1977), who
reported a good relationship between water uptake and rooting density. However, the directly
measured root length in this study was more
indicative than RLD. This may be due to the fact
that RLD was an estimate over the whole rooting
profile using root length, and radial and vertical
extensions of root systems, thus not taking into
account the root stratification within soil horizons. Theiveyanathan and Benyon (2000) associated the relatively high WU of Corymbia
123
maculata with the ability to develop high root
densities in the area of the capillary fringe.
The capacity of the root system of Eucalyptus
spp. to adapt to local environment was witnessed
by Knight (1999) who associated the ability of
these species to maintain a relatively high transpiration rate over dry periods to their dimorphic
root systems. The eucalypts combined deep roots
for taking up the groundwater with superficial
lateral roots for rainfall interception. The prevalence of high GWTs in Khorezm prevents trees to
develop taproots, as these may decay in conditions of elevated GWTs. Local and introduced
species (for the most part early last century)
tended to expand their roots horizontally and thus
developed a substantial length, particularly of fine
roots, which are the primary assimilators of water.
However, the tendency for horizontal root spread
may result in lower root densities, which can explain weak and negative correlations of RLD and
transpiration rates of the trees.
The relationship of transpiration rates with LA
was less important (r = 0.56) than that with root
length (r = 0.70), at least during the vital establishment phase. This does not correspond with
findings of Hatton et al. (1998); who, however,
measured transpiration of evergreen tree species
in closed stands. We suppose that under the agroclimatic conditions of the study region the root
formation was more essential during the early
growth of the young trees investigated, although
at a later stage the importance of LA is expected
to increase. Also, deciduous trees which produce
a new canopy each season cannot adjust their leaf
areas constantly and rapidly (Landsberg 1999a)
while the fine root turnover is very high (e.g.,
Santantonio 1990).
The variability in transpiration rates per unit
LA among tree species even under ample water
availability does not support findings of Hatton
et al. (1998) who postulated that transpiration
rates were independent of species. Yet, even
when water stress, which alters stomata behavior
of drought-sensitive species, is excluded, speciesdependant physiological features, such as tolerance to salinity and poor drainage, do influence
transpiration rates. Naturally co-occurring species
may have come to the same long-term solution to
the water and salt stress and develop similar
Agroforest Syst
transpiration rates. However, all trees in the
agricultural area of Khorezm are deliberately
planted and therefore likely to retain their unique
adjustment mechanism.
These outcomes emphasize the strong influence
of species factor on WU and therefore suggest that
direct measurement of leaf transpiration of tree
species planted in salt-affected agricultural land in
Khorezm is preferable over the use of speciesindependent micrometeorological techniques; in
particular, since the latter may not be effective for
the estimation of evapotranspiration in heterogeneous stands (e.g., Schaeffer et al. 2000).
The findings at the sandy field suggest that in
years of sufficient water availability it is possible
to establish tree plantations with little surface
irrigation but with reliance on the GWT. However, given the strong dependency of GWTs on
the agricultural irrigation activities in the direct
surroundings (Ibrakhimov et al. 2004) and the
normally meager rainfall during the growing
season, relying on GWT alone for tree establishment may be insecure. Only after root system
establishment, trees can be expected to survive
solely on groundwater supply and have any biodrainage effect. Another problem related to the
sustainability of biodrainage plantations is that
GWT salinity is likely to rise if irrigation is discontinued, which adversely affects the most
salinity-sensitive species—a problem that yet
needs consideration if biodrainage is to be
successful.
Water use efficiency
Many WUE studies involving trees considered
aboveground DM (wood plus leaves) only. This
was often due to constraints associated with
quantifying the root fraction although some
studies successfully modeled root DM (e.g.,
McMurtrie et al. 1990). When ranking our
species according to their WUE, the sequence
substantially changed depending on whether the
considered DM component was the above-, the
below-ground biomass fraction or both. This
finding bears out the importance of incorporating
the below-ground fractions in tree WUE estimates in particular when WUE is an intended
criterion for species selection. However, when
water is not a limiting factor the species with a
maximal WU such as E. angustifolia must be
prioritized for purposes of biodrainage, even if
their WUE is low. This, therefore, restricts the
use of WUE as a selection factor for trees, which
are considered for reducing high GWTs.
Advocates of biological drainage plantations
often emphasize the low-cost aspects for the removal of excess water (Smedema 1997). Moreover, biodrainage plantations do not demand the
installation of physical structures, but can be
implemented by farmers themselves, who in
addition may gain marketable products such as
food, fodder, fiber and wood when adequate tree
species are chosen. These aspects are considered
to be a key element when one intends to convince
farmers to introduce new technologies (Landsberg 1999a). However, the fruit species tested
such as P. armeniaca and M. alba had a low potential for biodrainage purposes in the study region because of their salt sensitivity, low growth
rates and resulting low DM production and WU.
The tree species with largest WU and salinity
tolerance, and therefore most promising for biodrainage purposes under the agro-ecological
conditions in Khorezm, proved to be E. angustifolia, followed by U. pumila, P. euphratica and
P. nigra var. pyramidalis. In addition to the biodrainage potential, the fruit producing and
N-fixing E. angustifolia and, to a lesser extent,
U. pumila also ranked top as potential suppliers
of high quality supplementary fodder (Khamzina
et al. 2006) and, therefore, may provide concurrent economic advantages to farmers.
Conclusions
Evaluating the potential of various tree species
for bio-draining the saline hydromorphic soils of
Khorezm should be based on field data and involve WU, salinity tolerance, rooting characteristics, and LA of the trees.
Leaf transpiration rates of three-year-old trees
significantly varied among species. Transpiration
rates of tree species grown at sites with two soil
textures and sufficiently supplied with water were
highly correlated with the ability to produce and
elongate the root system. Correlation of WU with
123
Agroforest Syst
LA was less consistent at least in a heterogeneous
young stands.
The leading tree species with regards to their
WU, root growth, and adaptability to the natural
environment proved to be E. angustifolia followed by U. pumila, P. euphratica and P. nigra
var. pyramidalis, whereas fruit species such as
P. armeniaca and M. alba, though desirable from
the farmer’s economic viewpoint, showed low
biodrainage potential. However, since the N-fixing E. angustifolia and U. pumila have also
superior feed and firewood characteristics, they
may provide added value, which makes them the
most suitable candidates for afforestation and
biodrainage purposes.
Although the species behavior during the crucial establishment phase can be considered as a
prerequisite for tree further development, the
ranking of species based on the evaluation of 2- to
3-year-old trees may change over time. If the
observed variability in tree transpiration capacity
is confirmed during subsequent years it can be
used as a major criterion in selection of tree
species for the biodrainage purposes.
Acknowledgements The research was conducted within
the framework of German/Uzbek project ‘‘Economic and
ecological restructuring of land- and water use in the Region Khorezm (Uzbekistan): A pilot project in development research’’. The German Ministry for Education and
Research (BMBF; project number 0339970A), the Ministry for Schools, Science and Research of the State of
Northrhine-Westfalia financially supported this study.
Additional funds from German Academic Exchange Service (DAAD) are gratefully acknowledged. We are
thankful for the valuable comments from two anonymous
reviewers on the earlier version of this manuscript. This
paper is a revised, extended version of a presentation at
the 21st European Regional Meeting of the International
Commission on Irrigation and Drainage held in May 15–
19, 2005 in Frankfurt/Oder, Germany.
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