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| A comparison of pressure-volume curves with and without rehydration pretreatment in eight woody species of the semiarid Loess Plateau |
ORIGINAL PAPER
A comparison of pressure–volume curves
with and without rehydration pretreatment in eight
woody species of the semiarid Loess Plateau
Mei-Jie Yan • Makiko Yamamoto • Norikazu Yamanaka •
Fukuju Yamamoto • Guo-Bin Liu • Sheng Du
Received: 21 February 2012 / Revised: 29 September 2012 / Accepted: 26 October 2012 / Published online: 7 November 2012
Franciszek Go´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako´w 2012
Abstract Pressure–volume (P–V) curves are frequently
used to analyze water relation properties of woody plants in
response to transpiration-induced tissue water loss. In this
study, P–V analyses were conducted on eight woody
species growing in the semiarid Loess Plateau region of
China during a relatively dry summer season using both the
recently recommended instantaneous measurement and the
traditional method with rehydration pretreatment. Generally,
P–V-derived parameters in this study reflected conditions
in a dry growth environment. Species-specific
differences were also found among P–V parameters, suggesting
each species uses different mechanisms to respond
to drought. Based on the results from instantaneous measurements,
a descending sequence for drought tolerance
ranked by water potentials at the turgor loss point (Wtlp)
was Rosa hugonis[Syringa oblata = Armeniaca sibirica[
Caragana microphylla[Pyrus betulaefolia[Acer
stenolobum[Quercus liaotungensis[Robinia pseudoacacia.
The first five species also showed lower levels of
osmotic potential at full turgor (Wp
sat) and higher symplastic
osmotic solute content per dry weight, suggesting they
possess advantages in osmotic adjustment. Also, this study
supports previous reports noting rehydration pretreatment
resulted in shifts in P–V parameters. The magnitude of the
shifts varied with species and water conditions. The effect
of rehydration was stronger for species with higher drought
tolerance or subjected to the influence of drought. Differences
in the parameters among species were mitigated as a
result of rehydration. Those with a lower Wtlp or midday
water potential were more deeply affected by rehydration.
Application of instantaneous measurements was strongly
recommended for proper analysis of P–V curves particularly
in arid and semiarid areas.
Keywords Drought tolerance Loess Plateau Pressure–
volume curves Rehydration Semiarid Water relations
Abbreviations
RWC Relative water content
RWCtlp Relative water content at turgor loss point
SWC Relative symplastic water content
SWCtlp Relative symplastic water content at turgor loss
point
NsDW-1 Symplast osmotic solute content per dry
weight
V0DW-1 Symplastic water at full turgor per dry weight
V0 Relative symplastic water content
Va Relative apoplastic water content
W Water potential
Wpd Water potential at predawn
M.-J. Yan and M. Yamamoto contributed equally to this work
Communicated by J. Franklin.
M.-J. Yan M. Yamamoto G.-B. Liu S. Du
State Key Laboratory of Soil Erosion and Dryland Farming
on Loess Plateau, Institute of Soil and Water Conservation,
Northwest A&F University, Yangling,
Shaanxi 712100, China
M.-J. Yan M. Yamamoto G.-B. Liu S. Du (&)
Institute of Soil and Water Conservation, Chinese Academy
of Sciences and Ministry of Water Resources, Yangling,
Shaanxi 712100, China
e-mail: shengdu@ms.iswc.ac.cn
N. Yamanaka
Arid Land Research Center, Tottori University,
Tottori 680-0001, Japan
F. Yamamoto
Faculty of Agriculture, Tottori University,
Tottori 680-8553, Japan
123
Acta Physiol Plant (2013) 35:1051–1060
DOI 10.1007/s11738-012-1143-3
Wmd Water potential at midday
Wtlp Water potential at turgor loss point
Wp Pressure potential
Wp Osmotic potential
Wp
sat Osmotic potential at water saturation with full
turgor
e Bulk elastic modulus
emax Maximum bulk elastic modulus
Introduction
Ci and Wu (1997) estimated that more than a third of China
was composed of arid and semiarid lands. Vegetation in
these areas is subjected to frequent stress from soil water
shortages and the dry climate. In the semiarid Loess
Plateau region of north-central China, easily eroded
soils, aridity, and human activities have caused severe soil
erosion and vegetation degradation. Rehabilitating and
stabilizing these ecosystems is a major task related to forest
and grassland management in the region.
Reforestation of semiarid land requires using selected
species that can provide sustainable long-term ecological
services. Eco-physiological properties of trees are commonly
considered when their capacity for growth and stress
tolerance are evaluated (Kozlowski and Pallardy 1997;
Larcher 2003). Several characteristics have been addressed
as being potentially responsible for the adaptability of tree
species to dryland environments. These characteristics
include, for example, the xerophytic structure of leaves,
well-developed root systems, stems with high hydraulic
conductivity and low cavitation risk, the ability to endure
extremely low water potentials, stomatal control of transpiration,
osmotic adjustment, activation of anti-oxidative
enzymes, and possession of stiff cell walls (Kozlowski
1976; Kozlowski and Pallardy 1997; Larcher 2003). Several
investigators have studied forest species growing in the
central Loess Plateau region regarding their photosynthetic
and water consumption responses to drought stress (Hara
et al. 2008; Yan et al. 2010; Du et al. 2011). However, the
investigation of water relation characteristics for in situ
individuals is still very limited.
Pressure–volume (P–V) curves, which are plotted using
measurements of leaf water potential (W) and relative water
content (RWC), have been widely applied as an important
approach in the evaluation of drought tolerance and drought
response patterns for trees and shrubs. Several parameters
derived from a P–V curve may indicate a species ability to
maintain cell turgor pressure under drying stress, or the
drought tolerance of a species. Generally, lower water
potential at the turgor loss point (Wtlp) is highly correlated
with lower osmotic potential at water saturation with full
turgor (Wp
sat). This means the species has a strong ability for
osmotic adjustment by having a large amount of osmotic
material in the cell sap. As drought may stimulate synthesis
and accumulation of osmotically effective constituents in
some species, a reduction in Wtlp may occur. Bulk elastic
modulus (e) reflects the rigidity of cell walls. Low e helps
tissues maintain their turgor during the process of water
loss, while high e means W drops rapidly during water loss
and the plant reaches Wtlp quickly, which may help the plant
absorb water during the early stages of water loss.
Two methods have been applied to the construction of
P–V curves. The traditional method includes a rehydration
pretreatment of plant materials (branches with leaves)
lasting from several to more than 24 h before the measurements
of leaf or xylem water potentials (Scholander
et al. 1965; Tyree and Hammel 1972). Thus, the measurements
are considered to start when the plant has full
turgor and cease after turgor loss. Since rehydration pretreatment
may lead to excessive apoplastic water uptake,
high estimates of osmotic potential (Wp) and low estimates
of relative water content at turgor loss point (RWCtlp) and e
have been detected (Evans et al. 1990; Meinzer et al.
1986). P–V parameters for rehydrated leaves shifted significantly
for plants under soil moisture stress (Kubiske and
Abrams 1991a, b). Seasonal variations and stress response
patterns may not be reflected by the results in such cases,
probably depending on the species involved, site conditions,
and rehydration time (Kubiske and Abrams 1991b).
Measurements with non-rehydrated samples have been
applied to the P–V analyses in recent years. To obtain the
changes in W components over a wide range of RWC,
researchers tend to start sampling and taking measurements
in the predawn hours when the tissues may have been
naturally rehydrated. However, shifts in P–V parameters
have also been detected even in naturally rehydrated leaves
and shoots (Parker and Pallardy 1987).
In the present study, we aimed (1) to comparatively
evaluate the water relation characteristics based on P–V
parameters for the common woody species in the region, and
(2) to assess the shifts (if any) in P–V parameters induced
during rehydration pretreatment. The results would contribute
to both a broader understanding of drought response
strategies for the species involved and proper application of
P–V techniques for plants in this semiarid environment.
Materials and methods
Study site and plant materials
The study was carried out at Mount Gonglushan (3625.400
N, 10931.530 E; 1353 m a.s.l.) near the city of Yan’an,
Shaanxi Province, in the semiarid Loess Plateau of central
1052 Acta Physiol Plant (2013) 35:1051–1060
123
China. This area is located on the forest-grassland transition
zone, where the forest ecosystems are subject to drought. The
mean annual precipitation and air temperature for
1982–2003 were 514 mm and 10.2 C, respectively, at a
meteorological station in nearby Yan’an. Spring and early
summer (from March to June) are usually dry in the area. July
and August are hot during the summer season but with
considerable precipitation. Otsuki et al. (2005) and Du et al.
(2007) provide detailed descriptions of the study site. Measurements
for this study were taken on relatively clear days
from 17 to 23 in August 2003. Rainfall occurred scarcely
during the 2 weeks before the measurements (Fig. 1).
Plant materials include six deciduous tree species, i.e.,
Robinia pseudoacacia L. (black locust), Quercus liaotungensis
Koidz. (Liaodong oak), Syringa oblata Lindl.
(early lilac), Acer stenolobum Rehd. (narrow crack maple),
Armeniaca sibirica Lam. (wild apricot), Pyrus betulaefolia
Bunge (birch-leaf pear), and two deciduous shrubs, i.e.,
Caragana microphylla Lam. (littleleaf peashrub) and Rosa
hugonis Hemsl. (Father Hugo rose). R. pseudoacacia trees
were planted for reforestation on abandoned farmland
20 years ago on an east-facing slope. Q. liaotungensis trees
were from a naturally developed stand about 50 years old
and facing northeast. Others were from the nearby natural
tree-shrub mixed vegetation around the ridge. Five sample
trees of relatively similar size were selected for each species
growing within 100 m from each other. Table 1 provides
mean heights and diameters at breast height of the
sample plants.
P–V curve analysis
Measurements for P–V analyses were performed using a
pressure chamber (Model 1000, PMS instruments
Corvallis, OR) during 17–20 August 2003, by periodically
measuring sample weight and W following the method
described in previous studies (Tyree and Hammel 1972;
Kubiske and Abrams 1990). Both rehydrated and nonrehydrated
leaves were measured for each sample tree for
comparison.
Sampling was conducted during predawn hours (around
4:00 h). Two terminal shoots with young, fully expanded
leaves were collected from each of five individuals for each
species. They were cut at 2–4 m height in the tall trees and
at 1.0–1.5 m height in the two shrubs. The shoots of
approximately 30–50 cm length were placed into a sealed
lightproof plastic bag with a moist paper towel and carried
to a nearby temporary laboratory. Each shoot for rehydration
pretreatment was recut under tap water and the base
hydrated in the dark for about 24 h before measurements.
Another shoot from the same individual was used for
instantaneous measurement in P–V analysis. An apical
twig was cut from each sample shoot for periodical
measurements.
0
5
10
15
20
25
30
35
40
1-Jul
7-Jul
13-Jul
19-Jul
25-Jul
31-Jul
6-Aug
12-Aug
18-Aug
24-Aug
30-Aug
Mean Max
0
10
20
30
40
50
60
Temperature (°C)
Precipitation (mm)
Min
Fig. 1 Daily mean (solid line
with filled diamond), maximum
(broken line with open
diamond), and minimum (dotted
line with multi symbol) air
temperature and daily
precipitation (solid bars) in July
and August in 2003 at Mt.
Gonglushan. Meteorological
instruments were set on a
nearby open space. Field
measurements for water
relations were carried out during
the 7 days (17–23 August)
indicated by the shaded area
Table 1 Mean (±standard errors) height and diameter at breast
height (DBH) of five sampled individuals for each species
Species Height (m) DBH (cm)
Robinia pseudoacacia 7.63 ± 0.33 11.30 ± 0.47
Quercus liaotungensis 6.69 ± 0.40 16.80 ± 3.53
Syringa oblata 3.36 ± 0.35 4.42 ± 0.58
Acer stenolobum 4.63 ± 0.52 7.47 ± 1.48
Armeniaca sibirica 4.10 ± 0.19 9.34 ± 1.82
Pyrus betulaefolia 6.04 ± 0.46 14.82 ± 1.93
Caragana microphylla 1.99 ± 0.05 0.96 ± 0.15
Rosa hugonis 1.68 ± 0.13 0.41 ± 0.13
Acta Physiol Plant (2013) 35:1051–1060 1053
123
Wtlp, Wp
sat, RWCtlp, relative symplastic water content at
turgor loss point (SWCtlp), relative symplastic water content
(V0), and relative apoplastic water content (Va) were
derived from P–V curves based on the work of Tyree and
Hammel (1972) and Kubiske and Abrams (1990, 1991b).
Symplastic water at full turgor per dry weight (V0DW-1) and
symplastic osmotic solute content per dry weight (NsDW-1)
were also estimated (Maury et al. 2000; Tognetti et al. 2000).
Maximum bulk elastic modulus (emax) was calculated following
Saito and Terashima (2004).
The saturated weight that is needed to calculate RWC
was determined using linear regression on data above the
turgor loss point in a plot of fresh weight versus water
potential. Because several P–V curves of the rehydrated
samples in some species contained a plateau region, the
linear regression excluded this region to avoid the ‘‘plateau
effect,’’ rehydration-induced shift in P–V curve parameters,
following Kubiske and Abrams (1990, 1991a) and Dichio
et al. (2003).
In situ measurements of water potentials
Water potentials at predawn (Wpd) and midday (Wmd) were
measured in situ at about 0400 and 1300 hours, respectively,
for each of the sampling individuals on 23 August
2003. Sampling was at the same height on the individuals
as that for P–V curve analysis. The measurement was
performed immediately after cutting.
Statistical analysis
Statistical analyses were performed using analysis of
variance. Water potentials and P–V parameters were
compared among species using Tukey’s honestly significant
difference test. For P–V parameters, paired t tests were
used to test the differences between rehydration treatment
and non-rehydration. Differences between Wmd and Wtlp
were also checked by paired t tests. Correlations among
P–V parameters and between P–V parameters and Wmd and
Wtlp were examined using Pearson (r) coefficient, considering
the individual values of all sample trees for either the
rehydrated or non-rehydrated method (n = 40). Analyses
were performed using R software for Windows (R Foundation
for Statistical Computing, Vienna, Austria).
Results and discussion
Predawn and midday water potentials
Species differences in Wpd and Wmd were observed
(Fig. 2). R. pseudoacacia and Q. liaotungensis showed
higher Wpd and Wmd than other species, though the
differences with some species were not statistically
significant. All the measured individuals for these two
species recovered their W to above -1.0 MPa by the predawn
measurement time. Also, A. stenolobum, P. betulaefolia
and C. microphylla also recovered relatively well
over the night. On the other hand, S. oblata, A. sibirica and
R. hugonis showed low values of both Wpd and Wmd,
suggesting a poor recovery of leaf water status throughout,
while C. microphylla showed a relatively high Wpd but the
Wmd dropped to a much lower level.
These two parameters might reflect several water-related
factors. High values of Wpd and Wmd are expected with
sufficient soil moisture, efficient water uptake and high
hydrological conductivities of the plants. Soil moisture
conditions may be reflected by Wpd very well. Water
-4.5
-3.6
-2.7
-1.8
-0.9
0.0
a
ab
b b
c c c
d
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
R pseudoacacia
Q liaotungensis
S oblata
A stenolobum
A sibirica
P betulaefolia
C microphylla
R hugonis
a a
a
ab ab
bc
c
c
Midday (MPa) Predawn (MPa)
Fig. 2 Water potential at predawn and midday of the eight woody
species growing at Mt. Gonglushan. Mean values and standard errors
(n = 5) are presented for each species. Bars with the same letters
are not significantly different among species (Tukey’s honestly
significant difference test, P\0.05)
1054 Acta Physiol Plant (2013) 35:1051–1060
123
uptake by root systems of S. oblata, A. sibirica and R.
hugonis was not able to compensate for their transpiration
loss. Also, Wmd may be more species-specific and also
reflect the condition of soil moisture stress. In general, Wmd
values in the present study were much lower than those
found in studies on plants growing at humid areas, suggesting
these ecosystems were water-limited. S. oblata, A.
sibirica, R. hugonis and C. microphylla in particular have
developed drought resistance.
P–V parameters and rehydration effects
Figure 3 shows typical Ho¨fler diagrams obtained from P–V
curves for the eight species, including instant
R pseudoacacia
Q liaotungensis
P betulaefolia
A sibirica
S oblata C microphylla
A stenolobum R hugonis
0
1
2
3
4
5
NR R
NR R
p NR p R
0
1
2
3
4
5
0
1
2
3
4
5
0
1
2
3
4
5
1.0 0.9 0.8 0.7 0.6 0.5
Relative symplastic water contents
1.0 0.9 0.8 0.7 0.6 0.5
| |, | |, | p| (MPa) | |, | |, | p| (MPa) | |, | |, | p| (MPa) | |, | |, | p| (MPa)
Fig. 3 Typical Ho¨fler
diagrams, relating water
potential (W; filled diamond,
open diamond), osmotic
potential (Wp; filled triangle,
open triangle), and pressure
potential (Wp; filled circle, open
circle), to relative symplastic
water contents from pressure–
volume curves of the eight
species using non-rehydrated
(NR; solid lines with closed
symbols) and rehydrated
(R; broken lines with opened
symbols) materials. Each
diagram includes a pair of
curves as a representative from
one of the five replicated
sampling individuals
Acta Physiol Plant (2013) 35:1051–1060 1055
123
measurements and rehydration pretreatment. These
diagrams represent dynamic changes of W, Wp, and Wp in
relation to relative symplastic water content (SWC).
Species differences in these P–V parameters can be found
in the diagrams. Ho¨fler diagrams particularly revealed
differences between instant measurements and rehydration
pretreatment. The plotted lines in the diagrams varied
widely from one to another in S. oblata, A. sibirica,
C. microphylla, and R. hugonis.
R. pseudoacacia, Q. liaotungensis and A. stenolobum
showed higher Wtlp and Wp
sat and lower NsDW-1 than the
other species (Table 2). Other P–V parameters did not rank
identically among species. Rehydration-induced shifts in
P–V parameters occurred in most of the species regardless
of correction for the ‘‘plateau effect.’’ Compared with
instantaneous measurement, rehydration masked differences
in several parameters (e.g., Wtlp, Wp
sat, and NsDW-1)
among species. Rehydration resulted in overestimates
of Wtlp in every species. The shifts were significant in
S. oblata, A. sibirica, P. betulaefolia, C. microphylla, and
R. hugonis (P\0.05, with asterisks). Wp
sat was also significantly
overestimated by rehydration in several species
Table 2 Water relation parameters derived from P–V curves for non-rehydrated and rehydrated materials of the eight woody species growing at
Mt. Gonglushan
Species Wtlp (MPa) Wp
sat (MPa)
Non-rehydrated Rehydrated Non-rehydrated Rehydrated
R. pseudoacacia -2.19 ± 0.08 a -2.04 ± 0.10 a -1.80 ± 0.07 a -1.77 ± 0.09 a
Q. liaotungensis -2.43 ± 0.06 a -2.37 ± 0.10 abc -2.17 ± 0.07 ab -2.04 ± 0.10 ab
S. oblata -3.33 ± 0.08* c -2.44 ± 0.07 abc -2.85 ± 0.08* c -2.03 ± 0.07 ab
A. stenolobum -2.72 ± 0.23 ab -2.24 ± 0.11 ab -2.18 ± 0.21 ab -1.91 ± 0.10 ab
A. sibirica -3.33 ± 0.05* c -2.82 ± 0.07 c -2.74 ± 0.10* bc -2.36 ± 0.07 b
P. betulaefolia -3.04 ± 0.13* bc -2.74 ± 0.16 bc -2.31 ± 0.11 ac -2.19 ± 0.16 ab
C. microphylla -3.19 ± 0.12* bc -2.16 ± 0.14 a -2.47 ± 0.21 bc -1.80 ± 0.16 ab
R. hugonis -3.49 ± 0.14* c -2.61 ± 0.11 bc -2.90 ± 0.18* c -2.05 ± 0.09 ab
Species RWCtlp SWCtlp
Non-rehydrated Rehydrated Non-rehydrated Rehydrated
R. pseudoacacia 0.89 ± 0.01 ab 0.90 ± 0.01 a 0.82 ± 0.02 ab 0.87 ± 0.01 a
Q. liaotungensis 0.93 ± 0.01* a 0.90 ± 0.00 a 0.89 ± 0.01 a 0.86 ± 0.01 ab
S. oblata 0.89 ± 0.01 ab 0.89 ± 0.01 a 0.86 ± 0.02 ab 0.83 ± 0.01 ac
A. stenolobum 0.89 ± 0.02 ab 0.92 ± 0.01 a 0.80 ± 0.02 ab 0.85 ± 0.02 ac
A. sibirica 0.89 ± 0.03 ab 0.91 ± 0.01 a 0.82 ± 0.02 ab 0.84 ± 0.01 ac
P. betulaefolia 0.88 ± 0.02 ab 0.90 ± 0.01 a 0.76 ± 0.03 b 0.80 ± 0.01 c
C. microphylla 0.81 ± 0.04 b 0.91 ± 0.01 a 0.77 ± 0.05 ab 0.83 ± 0.03 ac
R. hugonis 0.86 ± 0.02 ab 0.89 ± 0.00 a 0.83 ± 0.02 ab 0.79 ± 0.01 bc
Species NsDW-1 (osmoles kg-1DW) emax (MPa)
Non-rehydrated Rehydrated Non-rehydrated Rehydrated
R. pseudoacacia 0.74 ± 0.07 ab 0.89 ± 0.16 a 12.43 ± 1.69 b 15.54 ± 1.78 ab
Q. liaotungensis 0.63 ± 0.06 b 0.73 ± 0.09 a 17.30 ± 1.71 ab 18.54 ± 3.80 a
S. oblata 1.38 ± 0.14* a 0.92 ± 0.08 a 25.50 ± 3.66* a 11.52 ± 1.34 ab
A. stenolobum 0.64 ± 0.17 b 0.52 ± 0.05 a 14.87 ± 2.97 ab 10.94 ± 0.88 ab
A. sibirica 1.23 ± 0.13 ab 0.87 ± 0.08 a 18.77 ± 2.72 ab 15.09 ± 1.46 ab
P. betulaefolia 0.94 ± 0.23 ab 0.56 ± 0.11 a 10.41 ± 1.22 b 10.33 ± 2.18 ab
C. microphylla 1.17 ± 0.16 ab 0.61 ± 0.10 a 16.67 ± 5.69 ab 13.55 ± 0.93 ab
R. hugonis 1.12 ± 0.14* ab 0.52 ± 0.02 a 19.29 ± 3.52 ab 9.51 ± 0.38 b
Asterisks indicate a significant difference between the two methods (paired t test, P\0.05). Means (± SE, n = 5) with different letters in each
column indicate significant difference among species (Tukey’s honestly significant difference test, P\0.05). Parameters and their abbreviations
are as follows: water potential at turgor loss point (Wtlp), osmotic potential at water saturation with full turgor (Wp
sat), relative water content at
turgor loss point (RWCtlp), relative symplastic water content at turgor loss point (SWCtlp), symplastic osmotic solute content per dry weight
(NsDW-1), and maximum bulk elastic modulus (emax)
1056 Acta Physiol Plant (2013) 35:1051–1060
123
(S. oblata, A. sibirica, and R. hugonis). NsDW-1 was
underestimated by rehydration for all species excluding R.
pseudoacacia and Q. liaotungensis, and the underestimation
was significant in S. oblata and R. hugonis. Other
parameters showed relatively small differences between
rehydration and non-rehydration and among species.
The results of this study support previous reports where
rehydration resulted in shifts in P–V parameters, even after
the correction of the ‘‘plateau’’ effects. Also, rehydrationinduced
shifts masked seasonal variations in P–V parameters
that could be detected using instantaneous measurements
(Kubiske and Abrams 1991b). In addition, the effect of
rehydration was stronger for species with higher drought
tolerance or subjected to the influence of a droughty environment
(Evans et al. 1990; Kubiske and Abrams 1991a).
The magnitude of the shifts in the present study also varied
with species. Differences in the parameters among species
were mitigated consequently. Those with lower Wtlp
and Wmd, i.e., S. oblata, A. sibirica, C. microphylla, and
R. hugonis, showed a stronger influence by the rehydration
pretreatment.
In practice, full turgor does not occur under common
weather conditions (non-rainy) in arid and semiarid areas.
Artificial saturation in the laboratory may result in infiltration
of water into air spaces, causing unreasonable level
of RWC. Even re-watering the pot soil of water-stress
conditioned poplars had caused substantial reduction in
concentrations of some major solutes (Gebre et al. 1997).
As the rehydration-induced shifts might result from the
‘‘plateau’’ effects of excessive Va, correction of the
‘‘plateau’’ has been applied to P–V analyses (Dichio et al.
2003; Patakas et al. 2002; Warren et al. 2007). However,
such a correction turned out to be insufficient to eliminate
the influence. They may also be caused by the loss of
Table 3 Correlation values (Pearson’s r) of different parameters derived from the pressure–volume curves using non-rehydrated and rehydrated
materials
Wtlp Wp
sat NsDW-1 V0DW-1 RWCtlp SWCtlp Va
Non-rehydrated
Wp
sat 0.899**
NsDW-1 -0.783** -0.831**
V0DW-1 -0.572** -0.557** 0.914**
RWCtlp 0.286 -0.035 -0.078 -0.185
SWCtlp 0.034 -0.402* 0.262 0.089 0.674**
Va 0.445** 0.549** -0.536** -0.436** 0.429** -0.334*
emax -0.465** -0.754** 0.666** 0.443** 0.351* 0.737** -0.558**
Rehydrated
Wp
sat 0.913**
NsDW-1 -0.325* -0.532**
V0DW-1 -0.021 -0.225 0.939**
RWCtlp 0.453** 0.257 -0.391* -0.360*
SWCtlp 0.254 -0.159 0.448** 0.466** 0.508**
Va 0.096 0.353* -0.843** -0.846** 0.357* -0.591**
emax -0.070 -0.304 0.518** 0.459** 0.012 0.524** -0.637**
Abbreviations follow Table 2. Data sets cover individuals of all species (n = 40). Single and double asterisks indicate significance at levels of
P\0.05 and P\0.01, respectively
Table 4 Correlation values for P–V parameters versus predawn and
midday water potentials
Wpd Wmd
Non-rehydrated
Wtlp 0.641** 0.691**
Wp
sat 0.606** 0.629**
NsDW-1 -0.457** -0.558**
V0DW-1 -0.253 -0.407**
RWCtlp 0.121 0.208
SWCtlp -0.017 0.043
Va 0.206 0.282
emax 0.277 0.365*
Rehydrated
Wtlp 0.291 0.174
Wp
sat 0.197 0.062
NsDW-1 -0.105 -0.073
V0DW-1 -0.027 -0.040
RWCtlp 0.130 0.140
SWCtlp 0.246 0.292
Va -0.232 -0.267
emax -0.329* -0.361*
Abbreviations follow Table 2. Data sets cover individuals of all
species (n = 40). Single and double asterisks indicate significance at
levels of P\0.05 and P\0.01, respectively
Acta Physiol Plant (2013) 35:1051–1060 1057
123
symplastic solutes (Kubiske and Abrams 1991b). Lower
estimation of NsDW-1 and higher estimation of Va were
also observed in the rehydration treatments of the present
study, though results were statistically insignificant in
many species. For the materials in arid and semiarid areas,
or those subjected to water stress, osmotic substances
would accumulate and play important roles in the water
relation properties (Fernandez et al. 1999). In this case,
rehydration-caused solute loss would particularly mask the
real nature of the materials.
Relationships among P–V parameters
Correlation analyses for the parameters support the general
understanding that low Wtlp is strongly associated with low
Wp
sat which is affected by high NsDW-1, and high NsDW-1
is related to high V0DW-1 and low Va (Table 3). SWCtlp
and emax showed positive correlations. However, several
correlations that are significant for parameters of nonrehydration
became less significant or non-significant in
data with rehydration pretreatment. In contrast, a positive
relationship between Wtlp and RWCtlp was only seen to be
significant using the data with rehydration pretreatment.
There have been investigations on the synthesis of various
osmotic substances in response to drought and their
roles in Wp
sat (Clifford et al. 1998; Guignard et al. 2005;
Patakas et al. 2002; Warren et al. 2007). Increased
NsDW-1 was found to be accompanied by an increase in
V0 and decreases in Va and Wp
sat in oak leaves, suggesting a
role of osmotic solutes in the water distribution between
inside and outside the cells (Aranda et al. 2001). Also, a
seasonally observed increase in osmotic solutes was also
found to be accompanied by a redistribution of apoplastic
to symplastic water (Miki et al. 2003).
The rigidity of cell walls may be related to cell size and
wall composition and structure, and so affects a cell’s
tolerance to desiccation. Negative relationships were
observed in previous reports and this study between e and
both Wtlp and Wp
sat (Corcuera et al. 2002; Kubiske and
Abrams 1994; Ngugi et al. 2003; White et al. 2000).
Rehydration treatment may not only have affected Va,
NsDW-1, and RWCtlp, but also affected e.
Relationships between P–V parameters and water
potentials
Significant correlations were also observed for several P–V
parameters of non-rehydration with respect to Wpd and
Wmd, but not for parameters derived from rehydration
(Table 4). Both Wpd and Wmd were positively correlated
with Wtlp and Wp
sat, and negatively correlated with NsDW-1
and V0DW-1. This suggests P–V parameters substantially
coincide with the in situ water status of the species and
ecotypes. As Wmd is likely to be a reasonable representative
of minimum value throughout a day, the relationship
between Wmd and Wtlp was also analyzed (Fig. 4). For most
of the species, contrary to expectation, in situ measured
Wmd was even lower than Wtlp from P–V analysis. Wmd was
significantly lower than the value of Wtlp with rehydration
pretreatment for most of the species (Fig. 4b). These
results also agree with the shift of estimated parameters
from the measurements after rehydration, especially the
up-estimation for Wtlp. However, for non-rehydration, Wmd
and Wtlp values were not significantly different within
-1.6 -2.0 -2.4 -2.8 -3.2
Robinia pseudoacacia Quercus liaotungensis
Syringa oblata Acer stenolobum
Armeniaca sibirica Pyrus betulaefolia
Caragana microphylla Rosa hugonis
Y=X
-4.2
-3.8
-3.4
-3.0
-2.6
-2.2
-2.0 -2.4 -2.8 -3.2 -3.6 -4.0
Midday (MPa)
tlp rehydrat (MPa) tlp rehydrat (MPa)
*
* *
* *
*
*
*
a b
Fig. 4 Relationships between
midday water potential and
water potential at turgor loss
point (Wtlp) obtained from the
pressure–volume curves using
non-rehydrated (a) and
rehydrated (b) materials. Data
sets are presented as means and
standard errors (n = 5) for each
species. The dashed line
indicates Y = X. Asterisks
indicate significant difference
between Midday W and Wtlp
(paired t test, P\0.05)
1058 Acta Physiol Plant (2013) 35:1051–1060
123
individual species except for R. pseudoacacia and S. oblata
(Fig. 4a).
The present study was conducted during a period of
relative drought. The soil moisture had barely recharged by
effective rainfall over several weeks, while the evaporative
demands were much higher than the rainfall’s recharge
(Fig. 1). The measured lower values of Wmd suggest these
plants were subjected to drought. Species that have adapted
such environments may have strong ability of osmotic
adjustment in response to leaf water loss. R. pseudoacacia
and S. oblata, which showed large differences between
Wmd and estimated Wtlp, might have more actively transpired
during the daytime and thus suffer water deficiency
in their leaves. Some leaves in S. oblata were observed to
be withering during the midday measurement period.
Conclusion
This study was conducted on a site of semiarid area during
a drought period. Water relation characteristics of the six
tree species and two shrub species reflected their dry
growth environment. Wtlp and Wp
sat for all the species were
lower than those for plants growing at humid areas (e.g.,
Hara et al. 2008; Kubiske and Abrams 1994; Saito et al.
2003). Species-specific differences were also found among
P–V parameters, suggesting different species used different
drought response mechanisms. Based on the results from
non-rehydrated measurements, a descending sequence
for drought tolerance ranked by Wtlp was R. hugonis[
S. oblata = A. sibirica[C. microphylla[P. betulaefolia[
A. stenolobum[Q. liaotungensis[R. pseudoacacia.
The former five species showed Wtlp below -3 MPa,
indicating their tolerance to severe water stress. These
species also showed lower levels of Wp
sat and higher contents
of NsDW-1, suggesting their advantages in osmotic
adjustment. From the viewpoint of cell wall rigidity,
S. oblata, R. hugonis, A. sibirica and Q. liaotungensis
shared the characteristics of high emax, implying that their
W would rapidly decrease and the stoma would close at the
early stage of water deficiency. With relatively higher Wtlp
and Wp
sat, and lower emax, R. pseudoacacia would continuously
transpire during droughts and the cells tend to lose
their turgor earlier.
This study supports previous reports that rehydration
pretreatment resulted in shifts in P–V parameters. The
magnitude of the shifts varied with species and water
conditions. The effect of rehydration was stronger for
species with higher drought tolerance or subjected to the
influence of drought environment. Differences in the
parameters among species were mitigated as a result of
rehydration. Those with lower Wtlp and Wmd, i.e., S. oblata,
A. sibirica, C. microphylla, and R. hugonis, showed higher
influence by the rehydration treatment. Application of
instantaneous measurements was strongly recommended
for proper analysis of P–V curves particularly in arid and
semiarid areas.
Author contribution Mei-Jie Yan and Makiko
Yamamoto prepared the manuscript. Fukuju Yamamoto,
Norikazu Yamanaka and Sheng Du performed the field
measurements. Guo-Bin Liu and Sheng Du edited the
manuscript.
Acknowledgments This research has been supported by the
National Natural Science Foundation of China (No. 41171419), the
Knowledge Innovation Project of Chinese Academy of Sciences
(kzcx2-XB2-05, kzcx2-yw-BR-02), and the Core University
Exchange Program of Japan Society for the Promotion of Science.
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