Directory UMM :Data Elmu:jurnal:T:Tree Physiology:Vol16.1996:
Tree Physiology 16, 287--294
© 1996 Heron Publishing----Victoria, Canada
Comparative responses of cuttings and seedlings of Eucalyptus
globulus to water stress
JO SASSE1 and ROGER SANDS2,3
1
Forestry School, University of Melbourne, Creswick, Victoria 3363, Australia
2
Present address: School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New
Zealand
3
Author to whom correspondence should be addressed
Received March 2, 1995
Summary We compared responses of cuttings and seedlings
of Eucalyptus globulus Labill. subsp. globulus to water stress
in a 9-week greenhouse experiment. Optimal water availability
was achieved by watering pots daily to field capacity, and two
water stress treatments were imposed by reducing watering
frequency to every 6 or 14 days. Within each treatment, height
growth rates of cuttings and seedlings were similar, but the
water-stress treatments reduced growth rates by up to 15%.
Diameter growth rates were 25% lower in cuttings than in
seedlings under well-watered conditions and were reduced by
water stress in both plant types. Under well-watered conditions,
cuttings and seedlings used similar amounts of water, whereas
seedlings had greater water use (up to 28.5%) than cuttings in
both water-stress treatments. Shoot water relations of cuttings
and seedlings were similar over a range of soil water contents.
The responses of transpiration and stomatal conductance to soil
water content were similar in cuttings and seedlings. At the end
of the experiment, plants were left unwatered. Seedlings that
had been preconditioned by watering every 14 days survived
to lower soil water contents than seedlings from the well-watered treatment; however, cuttings from the water-stress treatments died at higher soil water contents than either seedlings
from the same treatment or cuttings from the well-watered
treatment. We conclude that exposure to moderate water stress
does not effectively precondition cuttings, and that their ability
to resist extreme water stress may be limited. These characteristics are probably associated with the root systems of cuttings which differ developmentally, architecturally and
anatomically from the root systems of seedlings.
Keywords: preconditioning, root systems, soil water content,
vegetative propagation, water relations.
Introduction
Eucalyptus globulus Labill. subsp. globulus is grown widely in
temperate zones because it grows quickly and has superior
pulp properties. Although stem cuttings are used for the multiplication and deployment of improved genotypes, the performance of cuttings compared to seedlings has not been evaluated.
It is important to establish whether cuttings can tolerate
equivalent conditions to seedlings, because the potential gains
of vegetative propagation will be negated if cuttings or plantlets cannot endure the conditions likely to be encountered in
the field (Struve et al. 1984, Kageyama and Kikuti 1989,
Karlsson and Russell 1990).
Because current plantation expansion in many countries is
onto sites with rainfall near the limits of a species’ ability to
survive and grow, resistance to water stress is an important
attribute of propagules; however, there have been few comparative studies of the resistance to water stress of cuttings and
seedlings. Harrison et al. (1989) found no differences in the
responses of peach (Prunus persica (L.) Batsch.) cuttings and
seedlings to water stress. Blake and Filho (1988) compared the
drought resistance of cuttings and seedlings of Eucalyptus
grandis W. Hill ex Maiden. and found significant differences
in several physiological parameters between cuttings and seedlings subjected to a 2.5-day drought. Cuttings had higher
stomatal conductances, lower minimum xylem pressure potentials and higher osmotic potentials at the turgor loss point than
seedlings, and were therefore regarded as less drought resistant
than seedlings. However, no data on soil water content, vapor
pressure deficit at measurement or predawn water potentials
were presented. In a follow-up study, Blake et al. (1988) found
that after 15 months in the field and after a period of 100 days
without rain, cuttings again had higher stomatal conductance,
transpiration and photosynthetic rates, and lower minimum
xylem pressure potentials than seedlings. The second study,
however, had similar limitations to the first study, and no data
on soil water status or atmospheric conditions were presented.
Ritchie et al. (1992) compared cuttings and seedlings of
Pseudotsuga menziesii (Mirb.) Franco and concluded that cuttings were a viable alternative to seedlings for planting stock,
because cuttings had greater stem diameters, root weights,
root/shoot ratios and diameter/height (sturdiness) ratios, and
were more cold hardy, more dormant, and had higher root
growth potential than seedlings. However, Grossnickle and
Russell (1990) predicted that cuttings would be less tolerant of
water stress than seedlings because of differences in anatomy
and hydraulic conductivity of the root systems of the two plant
288
SASSE AND SANDS
types. Mohammed and Vidaver (1991) found that tissue-cultured plantlets were more susceptible to water stress than
seedlings and proposed that this was due to differences in root
systems rather than physiological differences within the
shoots.
To determine whether propagation of plants from cuttings
alters their ability to resist drought, we analyzed the comparative responses of cuttings and seedlings of E. globulus to
imposed water stress under controlled conditions.
Materials and methods
Experimental design
The experiment was a randomized block design with five
replicates, three watering treatments and two plant types (one
ramet of each of two clones and one seedling) from three
families. A total of 135 plants was analyzed over 9 weeks.
Blocking was from north to south within the greenhouse,
because there were gradients in both light and temperature in
this direction.
Plant material
The cuttings and seedlings were from three families from the
breeding program of Celulose Beira Industrial (CELBI), Portugal. Cuttings were ramets of the two best rooting clones from
each family. The clones had average rooting abilities of over
70%. In October 1992, apical shoots, about 10--12 cm long,
were harvested from the clonal stock plants, and the apex and
surrounding leaf pairs up to about 1 cm long were removed.
The next leaf pair was retained whole and the following two
leaf pairs trimmed back to approximately 2 cm long. All other
leaf pairs were removed. The cuttings were dipped in 0.05%
benomyl fungicide (Benlate, 1g l −1) for 30 s, set into trays
containing forty 120-ml cavities filled with a 1/1 (v/v) mixture
of peat and perlite plus approximately 0.8 g of controlled-release fertilizer (Osmocote, N,P,K,S 17/4.4/10/4.1, 180-day-release) per cavity, and grown for 5 weeks in a greenhouse
providing a day/night air temperature of 24--26/20--22 °C, a
bench temperature of 24 °C, misting for 10 s every 12 min, and
50% shade.
In October 1992, seedlings were sown directly into the same
trays used for propagating cuttings. The growing medium was
a 7/3 (v/v) mixture of peat and perlite plus approximately 0.5
g of ‘‘Nurseryman’s Brand’’ fertilizer (N,P,K,S 5.3/3.6/8.0/8.0
plus trace elements) per cavity. The seedlings were watered
daily and 5 weeks after germination, liquid fertilizer (Aquasol,
N,P,K 23/4/18) was applied every 2 weeks.
On January 6, 1993, all cuttings and seedlings were measured for height, root-collar diameter and fresh weight, and then
transplanted to 5-l pots sealed to prevent drainage. Each pot
contained 775 g (dry weight) of a 7/3 (v/v) mix of peat and
perlite plus 25 g of 180-day-release Osmocote, and 1.3 l of
water was added to each pot to bring the water content of the
pot to field capacity (volumetric water capacity, θv = 0.289).
Coarse sand (400 g) was spread across the top of each pot to
minimize evaporation and the total weight recorded for use as
the target weight when returning pots to field capacity. All
plants were watered daily for the first 5 days after transplanting.
Treatments
From the sixth day after transplanting, plants were watered
either daily, every third day or weekly. At each watering, pots
were weighed and watered to their target weights. In addition,
15 pots without plants (one pot per treatment per replicate)
were weighed and watered at the same time as pots with plants
to estimate direct evaporative losses. Because the measurements of water potential, transpiration and stomatal conductance at Week 3 indicated that the plants were not suffering
from stress in any treatment, the frequency of watering in the
latter treatments was reduced from 3 and 7 days to 6 and 14
days, respectively, and henceforth these water-stress treatments are referred to as the 3/6-day and 7/14-day treatments.
The modified treatments commenced on January 31, 1993, and
continued for a further 6 weeks. The final watering occurred
on the same day for all treatments, and the plants were then left
unwatered and monitored until they reached the permanent
wilting point, i.e., the point when the plants could no longer
recover overnight from wilting during the day.
Measurements
Greenhouse conditions were recorded continuously on a mechanical thermohygrograph. The maximum daily temperature
in the greenhouse was generally between 28 and 30 °C, and the
minimum daily relative humidity was between 30 and 40%.
Plant heights and root-collar diameters were measured at transplanting, when the treatments changed, and after the final
watering. Mean relative growth rates were calculated for the
entire 9-week period. Before watering, pot weights were recorded to calculate water use. Total water use was calculated
as a ratio of plant height, which is closely correlated with leaf
area (Sasse 1994):
Wd =
W−V
,
H 1 + ((H2 − H 1)n)/t
i
(1)
where Wd is water use per unit height per day (ml cm −1 day −1),
W is measured water use (ml), V is evaporation directly from
the pots (ml), H1 is plant height at Time 1 (cm), H2 is plant
height at Time 2 (cm), t is the interval between Times 1 and 2
(days), n is the number of days since Time 1, and i is the
watering interval (days).
Transpiration (E) and stomatal conductance (gs) were measured with an LI-1600 steady state porometer (Li-Cor Inc.,
Lincoln, NE). Predawn and midday water potentials (Ψpredawn
and Ψmidday) were measured with a pressure chamber (PMS
Instruments, Corvallis, OR). Environmental conditions (temperature and relative humidity) were recorded at the time of
measurement, and the vapor pressure deficit (D) was calculated. Measurements were made over one drying cycle for each
treatment during the first 3 weeks and over another drying
cycle after the watering intervals were doubled. In the case of
the well-watered treatment, measurements were taken once, at
WATER STRESS IN EUCALYPTUS CUTTINGS AND SEEDLINGS
midday. Measurements of plants in the 3/6-day and 7/14-day
treatments were made over several days. Environmental conditions as measured by D differed between the days of measurement, making comparisons difficult. For comparative
purposes, a subsample of plants (all plants of Family CA from
all treatments and all replicates) was measured on the final day
of watering. To separate the effects of differing plant size, the
plants of Family CA were also evaluated when they reached a
water content of 200 ml (θv = 0.044). This residual water
content was selected because wilting occurred in well-watered
plants at approximately this water content. Pots were weighed
in the evening, and if they were close to their target weight
(within 25 g or 2%), they were measured the following day. In
addition to measurements of E, gs and water potentials, the
osmotic potential (Ψosmotic) of one leaf per plant was measured
with an HR33T dew point psychrometer equipped with a C-52
sample chamber (Wescor Inc., Logan, UT). At the point of
death, pots were weighed, and the soil water content determined.
Analysis
Data were analyzed by two-way analysis of variance to compare the effects of plant type and treatment, and their interactions. Family data were pooled because of the small sample
size, restricting comparisons to cuttings versus seedlings. Significant results were further analyzed by calculating the least
significant differences between means using the Student’s ttest. If data were heteroscedatic or non-normal, rank transformations were made before analysis. Responses of cuttings and
seedlings to changing soil water availability were analyzed by
evaluating each variable under a range of conditions, to allow
comparison of the responses of cuttings and seedlings to different conditions. Measurements made on the same day and at
the same residual water content were also analyzed.
289
Results
Growth rates and water use
Height growth rates were significantly lower in plants in the
3/6-day (12.7%) and 7/14-day (14.7%) treatments than in
plants in the well-watered treatment (Tables 1 and 2). There
was no significant difference between plant types, and no
significant interaction between treatment and plant type (Table 2).
Diameter growth rates of cuttings were significantly lower
(25.4%) than those of seedlings (Tables 2 and 3). Diameter
growth rates of both cuttings and seedlings were significantly
lower in the 3/6-day (cuttings 25.2%, seedlings 13.8%) and
7/14-day (cuttings 28.1%, seedlings 20.3%) treatments than in
the well-watered treatment, but the interaction was not significant.
Water use rates of cuttings and seedlings were similar in the
well-watered treatment (Figure 1, Table 2). Over the 9-week
study, the mean water use rates of seedlings and cuttings were
2.181 ml cm −1 day −1 (SE = 0.032) and 2.065 ml cm −1 day −1
(SE = 0.023), respectively. Fluctuations in the daily water use
were due to daily environmental fluctuations. After the change
in watering treatments on January 31, cuttings and seedlings in
the 3/6-day and 7/14-day treatments had significantly lower
water use rates than the well-watered plants. In addition, the
water use rates of seedlings in the 3/6-day and 7/14-day treatments were significantly higher than those of cuttings in the
comparable treatments (Table 2). The mean water use rates of
seedlings and cuttings in the 3/6-day treatment were 1.507 ml
cm −1 day −1 (SE = 0.038) and 1.173 ml cm −1 day −1 (SE =
0.029), respectively, which correspond to reductions of 30.9
and 43.2% compared with the water use rates of the well-watered control plants. Water use rates of plants in the 7/14-day
treatment were significantly lower than those of plants in the
Table 1. Mean heights (and standard errors) of cuttings and seedlings at transplanting and atWeeks 3 and 9 for each treatment, and mean relative
height growth rates (RH, week −1) for the period from transplanting to Week 9. The number of plants (n) within each treatment is shown.
Watering treatment
Plant type (n)
Daily
Cuttings (30)
Seedlings (15)
Cuttings (30)
Seedlings (15)
Cuttings (29)
Seedlings (15)
3/6-Day
7/14-Day
RH (week −1)
Height (cm)
Transplant
Week 3
Week 9
19.2 (0.52)
20.8 (0.65)
18.6 (0.59)
22.8 (0.66)
19.1 (0.63)
21.7 (0.95)
33.2 (0.84)
34.8 (0.62)
31.2 (1.08)
36.9 (0.80)
31.6 (1.00)
35.7 (1.29)
61.3 (1.64)
66.7 (2.12)
51.4 (2.06)
57.9 (2.28)
51.5 (1.53)
57.4 (2.28)
0.129 (0.003)
0.129 (0.005)
0.112 (0.003)
0.114 (0.005)
0.111 (0.003)
0.108 (0.004)
Table 2. Summary of analysis of variance of rank-transformed height and diameter growth ratesbetween transplanting and Week 9, and water use
rates. The P-values are presented for the main effects (plant type and watering treatment) and their interactions.
Source
df
Relative height growth rate
Relative diameter growth rate
Water use rate
Plant type (P)
Treatment (T)
P×T
1
2
2
0.9713
< 0.0001
0.8331
< 0.0001
< 0.0001
0.4823
< 0.0001
< 0.0001
0.0383
290
SASSE AND SANDS
Table 3. Mean root-collar diameters (and standard errors) of cuttings and seedlings at transplanting and at Weeks 3 and 9 for each treatment, and
the relative diameter growth rate (RD, week −1) between transplanting and Week 9. The number of plants (n) per treatment is shown.
Watering treatment
Daily
3/6-Day
7/14-Day
Plant type (n)
Cuttings (30)
Seedlings (15)
Cuttings (30)
Seedlings (15)
Cuttings (29)
Seedlings (15)
RD (week −1)
Diameter (mm)
Transplant
Week 3
Week 9
2.5 (0.10)
2.0 (0.09)
2.5 (0.08)
2.1 (0.06)
2.5 (0.08)
2.0 (0.08)
3.5 (0.10)
3.0 (0.13)
3.4 (0.07)
3.4 (0.11)
3.3 (0.08)
3.2 (0.13)
6.4 (0.21)
7.1 (0.38)
5.1 (0.21)
6.2 (0.29)
4.9 (0.17)
5.7 (0.27)
0.103 (0.005)
0.138 (0.005)
0.077 (0.005)
0.119 (0.004)
0.074 (0.005)
0.110 (0.006)
Figure 1. Mean water use per unit
height per day (ml cm −1 day −1)
and standard errors of cuttings and
seedlings for each treatment for
the period before each watering
event. The calculated water use is
the mean rate for the period prior
to watering, and each point is a watering event. Symbols: daily, seedling = s; 3/6-day, seedling = n;
7/14-day, seedling = h; daily, cutting = d; 3/6-day, cutting = m;
7/14-day, cutting = j.
other treatments, and the water use rates of cuttings remained
significantly lower than those of seedlings, although the difference was less than in the 3/6-day treatment. The mean rates of
water use of seedlings and cuttings in the 7/14-day treatment
were 1.178 ml cm −1 day −1 (SE = 0.031) and 1.011 ml cm −1
day −1 (SE = 0.023), respectively. These rates of water use were
21.8 and 13.8% below the rates of seedlings and cuttings in the
3/6-day treatment, and 54 and 51% lower than the rates for the
corresponding well-watered control plants. The interaction
between plant types and watering regime was significant (Table 2).
reduced to values of less than 500 mmol m −2 s −1. With further
reductions in soil water availability, gs fell to below 100 mmol
m −2 s −1. Responses of E to soil water availability were similar
to those of gs and did not differ between cuttings and seedlings.
Water relations----responses at a range of conditions
In both seedlings and cuttings, Ψmidday decreased as Ψpredawn
decreased, but the magnitude of the reduction decreased as
Ψpredawn declined (Figure 2). Stomatal conductance of wellwatered cuttings and seedlings responded exponentially to
changes in D (Figure 3). Although the responses of gs to θv
(Figure 4) and Ψpredawn (Figure 5) were confounded because
the measurements were taken on separate days at different
values of D, it was evident that, under well-watered conditions,
there was a large range in gs. At high D and θv, maximum gs
was around 1250 mmol m −2 s −1, but if θv fell below approximately 0.25 (about 86% of field capacity), gs was rapidly
Figure 2. Relationship between midday water potential and predawn
water potential measured on the same day. Results for cuttings and
seedlings are pooled; h = daily watering, d = 3/6-day watering, and
n = 7/14-day watering.
WATER STRESS IN EUCALYPTUS CUTTINGS AND SEEDLINGS
Figure 3. Response of stomatal conductance (gs) of well-watered
plants to changing vapor pressure deficit conditions. Cuttings and
seedlings have been pooled because there were no significant differences between the plant types. The data were obtained on January 11
(h), January 27 (d) and February 23 (n), 1993. The relationship
between the parameters is: gs = 683D −0.9 (r 2 = 0.85), where gs is
stomatal conductance (mmol H2O m −2 s −1) and D is vapor pressure
deficit (kPa).
291
Figure 5. Response of stomatal conductance to soil water availability
measured by predawn water potential. Cuttings and seedlings measured at the end of the watering cycle of all treatments have been
included; h = daily watering, d = 3/6-day watering, and n = 7/14-day
watering.
Water relations----measured on the same day
On the final day of watering, both E and gs were lower in plants
in the water-stress treatments than in well-watered plants (Table 4). The reductions were greater in cuttings than in seedlings; however, the cuttings were shorter than the seedlings and
hence, if cuttings and seedlings respond equally to reduced
water availability, the cuttings would not reduce soil water
availability as fast as the seedlings. Thus these data cannot
distinguish between differences that are a function of plant size
and therefore water content, and those that are a consequence
of plant propagation technique.
Water relations----measured at the same residual water
content
Figure 4. Response of stomatal conductance to soil water availability
measured by volumetric water content. Plants measured at the end of
the watering cycle of all treatments have been included. Field capacity
is 0.29; h = daily watering, d = 3/6-day watering, and n = 7/14-day
watering.
There were no significant differences in D for plants measured
at 200 ml residual water content (Tables 5 and 6), indicating
that all plants were assessed under similar conditions. Significant differences between treatments were found for Ψpredawn
and Ψmidday, but not for gs, E or Ψosmotic (Table 6). Water
potentials were significantly higher in plants in the 7/14-day
treatment than in the other treatments (Table 5). There was a
significant interaction between plant type and treatment in E,
and a strong interaction in gs (Table 6). In the well-watered
Table 4. Water relations of cuttings and seedlings at the end of the watering cycles of the three watering treatments measured on the same day.
Values of Ψpredawn (MPa), Ψmidday (MPa), E (mmol H2O m −2 s −1) and gs (mmol H2O m −2 s −1) are reported. Values of θv and D are included as an
indication of the conditions on the day of measurement. The number of plants (n) per treatment is shown.
Watering treatment
Plant type (n)
D
Ψpredawn
Ψmidday
E
gs
θv
Daily
Cuttings (15)
Seedlings (8)
Cuttings (16)
Seedlings (8)
Cuttings (16)
Seedlings (8)
1.803
1.845
1.890
2.111
2.162
2.221
−0.31
−0.32
−0.45
−0.51
−0.52
−0.80
−1.01
−1.03
−1.20
−1.16
−1.27
−1.48
19.044
16.311
15.568
11.308
8.417
5.520
1113
911
865
575
408
268
0.24
0.24
0.18
0.13
0.11
0.05
3/6-Day
7/14-Day
292
SASSE AND SANDS
Table 5. Water relations of the plants of Family CA at a residual water content of approximately 200 ml (θv = 0.044). Values of Ψpredawn (MPa),
Ψmidday (MPa), E (mmol H2O m −2 s −1), gs (mmol H2O m −2 s −1) and Ψosmotic (MPa) are reported. Values of θv and D are included as an indication
of the conditions on the day of measurement. The numbers of plants used for determining allparameters other than Ψosmotic are shown in brackets
next to the plant type. Numbers used to determine Ψosmotic are shown next to these values.
Watering treatment
Plant type (n)
θv
D
Ψpredawn
Ψmidday
E
gs
Ψosmotic
Daily
Cuttings (7)
Seedlings (5)
Cuttings (10)
Seedlings (5)
Cuttings (6)
Seedlings (5)
0.04
0.04
0.04
0.04
0.04
0.04
1.52
1.77
1.78
1.97
1.89
2.23
−1.63
−1.53
−1.38
−1.59
−1.01
−1.28
−2.23
−2.11
−2.07
−2.17
−1.75
−2.05
0.661
1.05
1.302
0.833
1.505
0.962
45.9
69.3
87.3
49.9
89.4
47.4
−5.46 (5)
−5.10 (2)
−3.99 (5)
−4.61 (4)
−3.46 (5)
−5.04 (5)
3/6-Day
7/14-Day
Table 6. Summary of the analysis of variance of the water relations parameters of the plantsof Family CA when measured at a mean residual water
content of 200 ml. Analysis of stomatal conductance and transpiration was performed with rank transformed data.
Source
θv
D
Ψpredawn
Ψmidday
E
gs
Ψosmotic
Plant type (P)
Treatment (T)
P×T
0.8745
0.8062
0.9703
0.1897
0.2476
0.9487
0.2453
0.0077
0.3668
0.3109
0.0372
0.1632
0.8512
0.2592
0.0283
0.6256
0.9905
0.0976
0.1517
0.1271
0.1871
treatment, both E and gs were lower in cuttings than in seedlings, whereas E and gs were higher in cuttings than in seedlings in the 3/6-day and 7/14-day treatments (Tables 5 and 6).
Also, E and gs were lower in well-watered cuttings than in
water-stressed cuttings, but higher in well-watered seedlings
than in water-stressed seedlings.
Discussion
Plant death
Cuttings and seedlings in the well-watered treatment died at
similar residual soil water contents (Table 7). Seedlings in the
7/14-day treatment died at a lower soil water content than
well-watered seedlings and seedlings in the 3/6-day treatment,
whereas cuttings in the water-stress treatments died at residual
soil water contents significantly higher than either well-watered cuttings or seedlings in the comparable water-stress treatment (Table 7). There were significant effects of plant type
(P < 0.0001) and treatment (P = 0.0124), and a strong interaction between plant type and treatment (P = 0.0804).
Under conditions of optimal water availability, we observed
few differences between cuttings and seedlings; however,
some differences emerged under conditions of imposed water
stress. Well-watered cuttings had slower diameter growth rates
than well-watered seedlings. Height and diameter growth rates
of both cuttings and seedlings were reduced by water stress. In
both of the water-stress treatments, water use by cuttings was
significantly less than that by seedlings. In contrast, instantaneous measurements of stomatal conductance showed that
there were no significant differences in the responses of cuttings and seedlings to reduced water availability. However,
reduced water availability did affect the water relations of
plants. Stomatal conductance was reduced by low soil water
availability. Stomatal conductance responded principally to
vapor pressure deficit when soil water content was above 86%
of field capacity (θv = 0.25). Below this threshold, the availability of soil water was the principal determinant of stomatal
conductance. Similar responses were found for transpiration.
The existence of a threshold below which stomatal conductance responds primarily to soil water content or leaf water
Table 7. Mean residual soil water content (ml) and standard errors, and the equivalent volumetric water content (θv) for cuttings and seedlings from
each treatment at the point of death. Plants from the Family CA have been excluded. The number of plants (n) per treatment is shown.
Daily
Residual soil water (ml)
SE
θv
3/6-Day
7/14-Day
Cuttings
(n = 30)
Seedlings
(n =15)
Cuttings
(n = 30)
Seedlings
(n = 14)
Cuttings
(n = 28)
Seedlings
(n = 14)
61
13
0.01
44
17
0.01
195
23
0.04
57
17
0.01
161
33
0.04
11
21
0.002
WATER STRESS IN EUCALYPTUS CUTTINGS AND SEEDLINGS
potential is typical of many herbaceous (Ludlow 1980, Bradford and Hsiao 1982) and woody (Jarvis 1980, Sands and
Mulligan 1990) plants. The threshold at which water availability becomes dominant in determining stomatal conductance
depends on the species and the environment, and typically the
threshold and the gradient of the decrease is higher in plants
grown in controlled conditions than in plants grown in the field
(Jarvis 1980, Ludlow 1980).
At very low soil water availability (200 ml residual soil
water content), there were significant differences in plant
water potentials between treatments, but not between cuttings
and seedlings. This contrasts with Blake and Filho’s (1988)
results in which cuttings of E. grandis had higher midday
water potentials than seedlings after 2.5 days of drought. This
difference may be a consequence of the preconditioning treatments that we imposed before measurement at a constant water
content. Preconditioning treatments change the physiological
responses of plants to water stress (Hsiao 1973). Assessment
of the water relations of cuttings and seedlings from each
watering treatment at the same water content indicated that
preconditioning occurred in both cuttings and seedlings. Water
potentials were between 0.3 and 0.4 MPa greater in plants from
the 7/14-day treatment than in plants from the other treatments.
However, cuttings and seedlings differed in their response to
preconditioning. Decreased water potentials were accompanied by decreased transpiration and stomatal conductance in
seedlings, and by increased transpiration and stomatal conductance in cuttings.
Effectively preconditioned plants would be expected to endure water stress better than nonconditioned plants, and this
was manifested in the seedlings as a reduction in transpiration
and stomatal conductance at low water availability and a reduced residual soil water content at which plant death occurred
in the 7/14-day treatment. However, a similar trend was not
found in the cuttings, suggesting that, under field conditions,
cuttings would be less likely to survive extreme water stress.
The similarity of the responses of shoots of cuttings and
seedlings to reduced soil water availability throughout this
experiment suggests that the differences in resistance to water
stress are due to differences in the functional capacities of the
root systems of the two plant types, i.e., water uptake and
transport. Uptake is dependent on the water available in the soil
and the water potential gradient imposed by the shoot, but is
also determined by the physiological, morphological and anatomical characteristics of the root system (Teskey 1991). The
morphology and anatomy of the root system of cuttings are
fundamentally different from those of seedlings, as a result of
their adventitious origin. The consequences of these differences are poorly understood because it is difficult to elucidate
the consequences of altered morphology in a seedling root
system on anchorage, and uptake and transport of water and
nutrients (Torrey and Clarkson 1975, Fitter 1991, Harper et al.
1991). It is even more difficult to predict the consequences of
the differences in the root systems of seedlings and cuttings.
However, it is important to note that some individual cuttings
did resist water stress in a similar way to seedlings, suggesting
that cuttings can develop a functionally effective root system.
293
With further evaluation of the development of the root system
of cuttings, it should be possible to modify the root system
during propagation to produce cuttings that are as resistant to
water stress as seedlings.
Acknowledgments
Plant material was provided by Celulose Beira Industrial (CELBI),
S.A., Portugal. This work was conducted when the first author was a
recipient of an Australian Postgraduate Research Award.
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© 1996 Heron Publishing----Victoria, Canada
Comparative responses of cuttings and seedlings of Eucalyptus
globulus to water stress
JO SASSE1 and ROGER SANDS2,3
1
Forestry School, University of Melbourne, Creswick, Victoria 3363, Australia
2
Present address: School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New
Zealand
3
Author to whom correspondence should be addressed
Received March 2, 1995
Summary We compared responses of cuttings and seedlings
of Eucalyptus globulus Labill. subsp. globulus to water stress
in a 9-week greenhouse experiment. Optimal water availability
was achieved by watering pots daily to field capacity, and two
water stress treatments were imposed by reducing watering
frequency to every 6 or 14 days. Within each treatment, height
growth rates of cuttings and seedlings were similar, but the
water-stress treatments reduced growth rates by up to 15%.
Diameter growth rates were 25% lower in cuttings than in
seedlings under well-watered conditions and were reduced by
water stress in both plant types. Under well-watered conditions,
cuttings and seedlings used similar amounts of water, whereas
seedlings had greater water use (up to 28.5%) than cuttings in
both water-stress treatments. Shoot water relations of cuttings
and seedlings were similar over a range of soil water contents.
The responses of transpiration and stomatal conductance to soil
water content were similar in cuttings and seedlings. At the end
of the experiment, plants were left unwatered. Seedlings that
had been preconditioned by watering every 14 days survived
to lower soil water contents than seedlings from the well-watered treatment; however, cuttings from the water-stress treatments died at higher soil water contents than either seedlings
from the same treatment or cuttings from the well-watered
treatment. We conclude that exposure to moderate water stress
does not effectively precondition cuttings, and that their ability
to resist extreme water stress may be limited. These characteristics are probably associated with the root systems of cuttings which differ developmentally, architecturally and
anatomically from the root systems of seedlings.
Keywords: preconditioning, root systems, soil water content,
vegetative propagation, water relations.
Introduction
Eucalyptus globulus Labill. subsp. globulus is grown widely in
temperate zones because it grows quickly and has superior
pulp properties. Although stem cuttings are used for the multiplication and deployment of improved genotypes, the performance of cuttings compared to seedlings has not been evaluated.
It is important to establish whether cuttings can tolerate
equivalent conditions to seedlings, because the potential gains
of vegetative propagation will be negated if cuttings or plantlets cannot endure the conditions likely to be encountered in
the field (Struve et al. 1984, Kageyama and Kikuti 1989,
Karlsson and Russell 1990).
Because current plantation expansion in many countries is
onto sites with rainfall near the limits of a species’ ability to
survive and grow, resistance to water stress is an important
attribute of propagules; however, there have been few comparative studies of the resistance to water stress of cuttings and
seedlings. Harrison et al. (1989) found no differences in the
responses of peach (Prunus persica (L.) Batsch.) cuttings and
seedlings to water stress. Blake and Filho (1988) compared the
drought resistance of cuttings and seedlings of Eucalyptus
grandis W. Hill ex Maiden. and found significant differences
in several physiological parameters between cuttings and seedlings subjected to a 2.5-day drought. Cuttings had higher
stomatal conductances, lower minimum xylem pressure potentials and higher osmotic potentials at the turgor loss point than
seedlings, and were therefore regarded as less drought resistant
than seedlings. However, no data on soil water content, vapor
pressure deficit at measurement or predawn water potentials
were presented. In a follow-up study, Blake et al. (1988) found
that after 15 months in the field and after a period of 100 days
without rain, cuttings again had higher stomatal conductance,
transpiration and photosynthetic rates, and lower minimum
xylem pressure potentials than seedlings. The second study,
however, had similar limitations to the first study, and no data
on soil water status or atmospheric conditions were presented.
Ritchie et al. (1992) compared cuttings and seedlings of
Pseudotsuga menziesii (Mirb.) Franco and concluded that cuttings were a viable alternative to seedlings for planting stock,
because cuttings had greater stem diameters, root weights,
root/shoot ratios and diameter/height (sturdiness) ratios, and
were more cold hardy, more dormant, and had higher root
growth potential than seedlings. However, Grossnickle and
Russell (1990) predicted that cuttings would be less tolerant of
water stress than seedlings because of differences in anatomy
and hydraulic conductivity of the root systems of the two plant
288
SASSE AND SANDS
types. Mohammed and Vidaver (1991) found that tissue-cultured plantlets were more susceptible to water stress than
seedlings and proposed that this was due to differences in root
systems rather than physiological differences within the
shoots.
To determine whether propagation of plants from cuttings
alters their ability to resist drought, we analyzed the comparative responses of cuttings and seedlings of E. globulus to
imposed water stress under controlled conditions.
Materials and methods
Experimental design
The experiment was a randomized block design with five
replicates, three watering treatments and two plant types (one
ramet of each of two clones and one seedling) from three
families. A total of 135 plants was analyzed over 9 weeks.
Blocking was from north to south within the greenhouse,
because there were gradients in both light and temperature in
this direction.
Plant material
The cuttings and seedlings were from three families from the
breeding program of Celulose Beira Industrial (CELBI), Portugal. Cuttings were ramets of the two best rooting clones from
each family. The clones had average rooting abilities of over
70%. In October 1992, apical shoots, about 10--12 cm long,
were harvested from the clonal stock plants, and the apex and
surrounding leaf pairs up to about 1 cm long were removed.
The next leaf pair was retained whole and the following two
leaf pairs trimmed back to approximately 2 cm long. All other
leaf pairs were removed. The cuttings were dipped in 0.05%
benomyl fungicide (Benlate, 1g l −1) for 30 s, set into trays
containing forty 120-ml cavities filled with a 1/1 (v/v) mixture
of peat and perlite plus approximately 0.8 g of controlled-release fertilizer (Osmocote, N,P,K,S 17/4.4/10/4.1, 180-day-release) per cavity, and grown for 5 weeks in a greenhouse
providing a day/night air temperature of 24--26/20--22 °C, a
bench temperature of 24 °C, misting for 10 s every 12 min, and
50% shade.
In October 1992, seedlings were sown directly into the same
trays used for propagating cuttings. The growing medium was
a 7/3 (v/v) mixture of peat and perlite plus approximately 0.5
g of ‘‘Nurseryman’s Brand’’ fertilizer (N,P,K,S 5.3/3.6/8.0/8.0
plus trace elements) per cavity. The seedlings were watered
daily and 5 weeks after germination, liquid fertilizer (Aquasol,
N,P,K 23/4/18) was applied every 2 weeks.
On January 6, 1993, all cuttings and seedlings were measured for height, root-collar diameter and fresh weight, and then
transplanted to 5-l pots sealed to prevent drainage. Each pot
contained 775 g (dry weight) of a 7/3 (v/v) mix of peat and
perlite plus 25 g of 180-day-release Osmocote, and 1.3 l of
water was added to each pot to bring the water content of the
pot to field capacity (volumetric water capacity, θv = 0.289).
Coarse sand (400 g) was spread across the top of each pot to
minimize evaporation and the total weight recorded for use as
the target weight when returning pots to field capacity. All
plants were watered daily for the first 5 days after transplanting.
Treatments
From the sixth day after transplanting, plants were watered
either daily, every third day or weekly. At each watering, pots
were weighed and watered to their target weights. In addition,
15 pots without plants (one pot per treatment per replicate)
were weighed and watered at the same time as pots with plants
to estimate direct evaporative losses. Because the measurements of water potential, transpiration and stomatal conductance at Week 3 indicated that the plants were not suffering
from stress in any treatment, the frequency of watering in the
latter treatments was reduced from 3 and 7 days to 6 and 14
days, respectively, and henceforth these water-stress treatments are referred to as the 3/6-day and 7/14-day treatments.
The modified treatments commenced on January 31, 1993, and
continued for a further 6 weeks. The final watering occurred
on the same day for all treatments, and the plants were then left
unwatered and monitored until they reached the permanent
wilting point, i.e., the point when the plants could no longer
recover overnight from wilting during the day.
Measurements
Greenhouse conditions were recorded continuously on a mechanical thermohygrograph. The maximum daily temperature
in the greenhouse was generally between 28 and 30 °C, and the
minimum daily relative humidity was between 30 and 40%.
Plant heights and root-collar diameters were measured at transplanting, when the treatments changed, and after the final
watering. Mean relative growth rates were calculated for the
entire 9-week period. Before watering, pot weights were recorded to calculate water use. Total water use was calculated
as a ratio of plant height, which is closely correlated with leaf
area (Sasse 1994):
Wd =
W−V
,
H 1 + ((H2 − H 1)n)/t
i
(1)
where Wd is water use per unit height per day (ml cm −1 day −1),
W is measured water use (ml), V is evaporation directly from
the pots (ml), H1 is plant height at Time 1 (cm), H2 is plant
height at Time 2 (cm), t is the interval between Times 1 and 2
(days), n is the number of days since Time 1, and i is the
watering interval (days).
Transpiration (E) and stomatal conductance (gs) were measured with an LI-1600 steady state porometer (Li-Cor Inc.,
Lincoln, NE). Predawn and midday water potentials (Ψpredawn
and Ψmidday) were measured with a pressure chamber (PMS
Instruments, Corvallis, OR). Environmental conditions (temperature and relative humidity) were recorded at the time of
measurement, and the vapor pressure deficit (D) was calculated. Measurements were made over one drying cycle for each
treatment during the first 3 weeks and over another drying
cycle after the watering intervals were doubled. In the case of
the well-watered treatment, measurements were taken once, at
WATER STRESS IN EUCALYPTUS CUTTINGS AND SEEDLINGS
midday. Measurements of plants in the 3/6-day and 7/14-day
treatments were made over several days. Environmental conditions as measured by D differed between the days of measurement, making comparisons difficult. For comparative
purposes, a subsample of plants (all plants of Family CA from
all treatments and all replicates) was measured on the final day
of watering. To separate the effects of differing plant size, the
plants of Family CA were also evaluated when they reached a
water content of 200 ml (θv = 0.044). This residual water
content was selected because wilting occurred in well-watered
plants at approximately this water content. Pots were weighed
in the evening, and if they were close to their target weight
(within 25 g or 2%), they were measured the following day. In
addition to measurements of E, gs and water potentials, the
osmotic potential (Ψosmotic) of one leaf per plant was measured
with an HR33T dew point psychrometer equipped with a C-52
sample chamber (Wescor Inc., Logan, UT). At the point of
death, pots were weighed, and the soil water content determined.
Analysis
Data were analyzed by two-way analysis of variance to compare the effects of plant type and treatment, and their interactions. Family data were pooled because of the small sample
size, restricting comparisons to cuttings versus seedlings. Significant results were further analyzed by calculating the least
significant differences between means using the Student’s ttest. If data were heteroscedatic or non-normal, rank transformations were made before analysis. Responses of cuttings and
seedlings to changing soil water availability were analyzed by
evaluating each variable under a range of conditions, to allow
comparison of the responses of cuttings and seedlings to different conditions. Measurements made on the same day and at
the same residual water content were also analyzed.
289
Results
Growth rates and water use
Height growth rates were significantly lower in plants in the
3/6-day (12.7%) and 7/14-day (14.7%) treatments than in
plants in the well-watered treatment (Tables 1 and 2). There
was no significant difference between plant types, and no
significant interaction between treatment and plant type (Table 2).
Diameter growth rates of cuttings were significantly lower
(25.4%) than those of seedlings (Tables 2 and 3). Diameter
growth rates of both cuttings and seedlings were significantly
lower in the 3/6-day (cuttings 25.2%, seedlings 13.8%) and
7/14-day (cuttings 28.1%, seedlings 20.3%) treatments than in
the well-watered treatment, but the interaction was not significant.
Water use rates of cuttings and seedlings were similar in the
well-watered treatment (Figure 1, Table 2). Over the 9-week
study, the mean water use rates of seedlings and cuttings were
2.181 ml cm −1 day −1 (SE = 0.032) and 2.065 ml cm −1 day −1
(SE = 0.023), respectively. Fluctuations in the daily water use
were due to daily environmental fluctuations. After the change
in watering treatments on January 31, cuttings and seedlings in
the 3/6-day and 7/14-day treatments had significantly lower
water use rates than the well-watered plants. In addition, the
water use rates of seedlings in the 3/6-day and 7/14-day treatments were significantly higher than those of cuttings in the
comparable treatments (Table 2). The mean water use rates of
seedlings and cuttings in the 3/6-day treatment were 1.507 ml
cm −1 day −1 (SE = 0.038) and 1.173 ml cm −1 day −1 (SE =
0.029), respectively, which correspond to reductions of 30.9
and 43.2% compared with the water use rates of the well-watered control plants. Water use rates of plants in the 7/14-day
treatment were significantly lower than those of plants in the
Table 1. Mean heights (and standard errors) of cuttings and seedlings at transplanting and atWeeks 3 and 9 for each treatment, and mean relative
height growth rates (RH, week −1) for the period from transplanting to Week 9. The number of plants (n) within each treatment is shown.
Watering treatment
Plant type (n)
Daily
Cuttings (30)
Seedlings (15)
Cuttings (30)
Seedlings (15)
Cuttings (29)
Seedlings (15)
3/6-Day
7/14-Day
RH (week −1)
Height (cm)
Transplant
Week 3
Week 9
19.2 (0.52)
20.8 (0.65)
18.6 (0.59)
22.8 (0.66)
19.1 (0.63)
21.7 (0.95)
33.2 (0.84)
34.8 (0.62)
31.2 (1.08)
36.9 (0.80)
31.6 (1.00)
35.7 (1.29)
61.3 (1.64)
66.7 (2.12)
51.4 (2.06)
57.9 (2.28)
51.5 (1.53)
57.4 (2.28)
0.129 (0.003)
0.129 (0.005)
0.112 (0.003)
0.114 (0.005)
0.111 (0.003)
0.108 (0.004)
Table 2. Summary of analysis of variance of rank-transformed height and diameter growth ratesbetween transplanting and Week 9, and water use
rates. The P-values are presented for the main effects (plant type and watering treatment) and their interactions.
Source
df
Relative height growth rate
Relative diameter growth rate
Water use rate
Plant type (P)
Treatment (T)
P×T
1
2
2
0.9713
< 0.0001
0.8331
< 0.0001
< 0.0001
0.4823
< 0.0001
< 0.0001
0.0383
290
SASSE AND SANDS
Table 3. Mean root-collar diameters (and standard errors) of cuttings and seedlings at transplanting and at Weeks 3 and 9 for each treatment, and
the relative diameter growth rate (RD, week −1) between transplanting and Week 9. The number of plants (n) per treatment is shown.
Watering treatment
Daily
3/6-Day
7/14-Day
Plant type (n)
Cuttings (30)
Seedlings (15)
Cuttings (30)
Seedlings (15)
Cuttings (29)
Seedlings (15)
RD (week −1)
Diameter (mm)
Transplant
Week 3
Week 9
2.5 (0.10)
2.0 (0.09)
2.5 (0.08)
2.1 (0.06)
2.5 (0.08)
2.0 (0.08)
3.5 (0.10)
3.0 (0.13)
3.4 (0.07)
3.4 (0.11)
3.3 (0.08)
3.2 (0.13)
6.4 (0.21)
7.1 (0.38)
5.1 (0.21)
6.2 (0.29)
4.9 (0.17)
5.7 (0.27)
0.103 (0.005)
0.138 (0.005)
0.077 (0.005)
0.119 (0.004)
0.074 (0.005)
0.110 (0.006)
Figure 1. Mean water use per unit
height per day (ml cm −1 day −1)
and standard errors of cuttings and
seedlings for each treatment for
the period before each watering
event. The calculated water use is
the mean rate for the period prior
to watering, and each point is a watering event. Symbols: daily, seedling = s; 3/6-day, seedling = n;
7/14-day, seedling = h; daily, cutting = d; 3/6-day, cutting = m;
7/14-day, cutting = j.
other treatments, and the water use rates of cuttings remained
significantly lower than those of seedlings, although the difference was less than in the 3/6-day treatment. The mean rates of
water use of seedlings and cuttings in the 7/14-day treatment
were 1.178 ml cm −1 day −1 (SE = 0.031) and 1.011 ml cm −1
day −1 (SE = 0.023), respectively. These rates of water use were
21.8 and 13.8% below the rates of seedlings and cuttings in the
3/6-day treatment, and 54 and 51% lower than the rates for the
corresponding well-watered control plants. The interaction
between plant types and watering regime was significant (Table 2).
reduced to values of less than 500 mmol m −2 s −1. With further
reductions in soil water availability, gs fell to below 100 mmol
m −2 s −1. Responses of E to soil water availability were similar
to those of gs and did not differ between cuttings and seedlings.
Water relations----responses at a range of conditions
In both seedlings and cuttings, Ψmidday decreased as Ψpredawn
decreased, but the magnitude of the reduction decreased as
Ψpredawn declined (Figure 2). Stomatal conductance of wellwatered cuttings and seedlings responded exponentially to
changes in D (Figure 3). Although the responses of gs to θv
(Figure 4) and Ψpredawn (Figure 5) were confounded because
the measurements were taken on separate days at different
values of D, it was evident that, under well-watered conditions,
there was a large range in gs. At high D and θv, maximum gs
was around 1250 mmol m −2 s −1, but if θv fell below approximately 0.25 (about 86% of field capacity), gs was rapidly
Figure 2. Relationship between midday water potential and predawn
water potential measured on the same day. Results for cuttings and
seedlings are pooled; h = daily watering, d = 3/6-day watering, and
n = 7/14-day watering.
WATER STRESS IN EUCALYPTUS CUTTINGS AND SEEDLINGS
Figure 3. Response of stomatal conductance (gs) of well-watered
plants to changing vapor pressure deficit conditions. Cuttings and
seedlings have been pooled because there were no significant differences between the plant types. The data were obtained on January 11
(h), January 27 (d) and February 23 (n), 1993. The relationship
between the parameters is: gs = 683D −0.9 (r 2 = 0.85), where gs is
stomatal conductance (mmol H2O m −2 s −1) and D is vapor pressure
deficit (kPa).
291
Figure 5. Response of stomatal conductance to soil water availability
measured by predawn water potential. Cuttings and seedlings measured at the end of the watering cycle of all treatments have been
included; h = daily watering, d = 3/6-day watering, and n = 7/14-day
watering.
Water relations----measured on the same day
On the final day of watering, both E and gs were lower in plants
in the water-stress treatments than in well-watered plants (Table 4). The reductions were greater in cuttings than in seedlings; however, the cuttings were shorter than the seedlings and
hence, if cuttings and seedlings respond equally to reduced
water availability, the cuttings would not reduce soil water
availability as fast as the seedlings. Thus these data cannot
distinguish between differences that are a function of plant size
and therefore water content, and those that are a consequence
of plant propagation technique.
Water relations----measured at the same residual water
content
Figure 4. Response of stomatal conductance to soil water availability
measured by volumetric water content. Plants measured at the end of
the watering cycle of all treatments have been included. Field capacity
is 0.29; h = daily watering, d = 3/6-day watering, and n = 7/14-day
watering.
There were no significant differences in D for plants measured
at 200 ml residual water content (Tables 5 and 6), indicating
that all plants were assessed under similar conditions. Significant differences between treatments were found for Ψpredawn
and Ψmidday, but not for gs, E or Ψosmotic (Table 6). Water
potentials were significantly higher in plants in the 7/14-day
treatment than in the other treatments (Table 5). There was a
significant interaction between plant type and treatment in E,
and a strong interaction in gs (Table 6). In the well-watered
Table 4. Water relations of cuttings and seedlings at the end of the watering cycles of the three watering treatments measured on the same day.
Values of Ψpredawn (MPa), Ψmidday (MPa), E (mmol H2O m −2 s −1) and gs (mmol H2O m −2 s −1) are reported. Values of θv and D are included as an
indication of the conditions on the day of measurement. The number of plants (n) per treatment is shown.
Watering treatment
Plant type (n)
D
Ψpredawn
Ψmidday
E
gs
θv
Daily
Cuttings (15)
Seedlings (8)
Cuttings (16)
Seedlings (8)
Cuttings (16)
Seedlings (8)
1.803
1.845
1.890
2.111
2.162
2.221
−0.31
−0.32
−0.45
−0.51
−0.52
−0.80
−1.01
−1.03
−1.20
−1.16
−1.27
−1.48
19.044
16.311
15.568
11.308
8.417
5.520
1113
911
865
575
408
268
0.24
0.24
0.18
0.13
0.11
0.05
3/6-Day
7/14-Day
292
SASSE AND SANDS
Table 5. Water relations of the plants of Family CA at a residual water content of approximately 200 ml (θv = 0.044). Values of Ψpredawn (MPa),
Ψmidday (MPa), E (mmol H2O m −2 s −1), gs (mmol H2O m −2 s −1) and Ψosmotic (MPa) are reported. Values of θv and D are included as an indication
of the conditions on the day of measurement. The numbers of plants used for determining allparameters other than Ψosmotic are shown in brackets
next to the plant type. Numbers used to determine Ψosmotic are shown next to these values.
Watering treatment
Plant type (n)
θv
D
Ψpredawn
Ψmidday
E
gs
Ψosmotic
Daily
Cuttings (7)
Seedlings (5)
Cuttings (10)
Seedlings (5)
Cuttings (6)
Seedlings (5)
0.04
0.04
0.04
0.04
0.04
0.04
1.52
1.77
1.78
1.97
1.89
2.23
−1.63
−1.53
−1.38
−1.59
−1.01
−1.28
−2.23
−2.11
−2.07
−2.17
−1.75
−2.05
0.661
1.05
1.302
0.833
1.505
0.962
45.9
69.3
87.3
49.9
89.4
47.4
−5.46 (5)
−5.10 (2)
−3.99 (5)
−4.61 (4)
−3.46 (5)
−5.04 (5)
3/6-Day
7/14-Day
Table 6. Summary of the analysis of variance of the water relations parameters of the plantsof Family CA when measured at a mean residual water
content of 200 ml. Analysis of stomatal conductance and transpiration was performed with rank transformed data.
Source
θv
D
Ψpredawn
Ψmidday
E
gs
Ψosmotic
Plant type (P)
Treatment (T)
P×T
0.8745
0.8062
0.9703
0.1897
0.2476
0.9487
0.2453
0.0077
0.3668
0.3109
0.0372
0.1632
0.8512
0.2592
0.0283
0.6256
0.9905
0.0976
0.1517
0.1271
0.1871
treatment, both E and gs were lower in cuttings than in seedlings, whereas E and gs were higher in cuttings than in seedlings in the 3/6-day and 7/14-day treatments (Tables 5 and 6).
Also, E and gs were lower in well-watered cuttings than in
water-stressed cuttings, but higher in well-watered seedlings
than in water-stressed seedlings.
Discussion
Plant death
Cuttings and seedlings in the well-watered treatment died at
similar residual soil water contents (Table 7). Seedlings in the
7/14-day treatment died at a lower soil water content than
well-watered seedlings and seedlings in the 3/6-day treatment,
whereas cuttings in the water-stress treatments died at residual
soil water contents significantly higher than either well-watered cuttings or seedlings in the comparable water-stress treatment (Table 7). There were significant effects of plant type
(P < 0.0001) and treatment (P = 0.0124), and a strong interaction between plant type and treatment (P = 0.0804).
Under conditions of optimal water availability, we observed
few differences between cuttings and seedlings; however,
some differences emerged under conditions of imposed water
stress. Well-watered cuttings had slower diameter growth rates
than well-watered seedlings. Height and diameter growth rates
of both cuttings and seedlings were reduced by water stress. In
both of the water-stress treatments, water use by cuttings was
significantly less than that by seedlings. In contrast, instantaneous measurements of stomatal conductance showed that
there were no significant differences in the responses of cuttings and seedlings to reduced water availability. However,
reduced water availability did affect the water relations of
plants. Stomatal conductance was reduced by low soil water
availability. Stomatal conductance responded principally to
vapor pressure deficit when soil water content was above 86%
of field capacity (θv = 0.25). Below this threshold, the availability of soil water was the principal determinant of stomatal
conductance. Similar responses were found for transpiration.
The existence of a threshold below which stomatal conductance responds primarily to soil water content or leaf water
Table 7. Mean residual soil water content (ml) and standard errors, and the equivalent volumetric water content (θv) for cuttings and seedlings from
each treatment at the point of death. Plants from the Family CA have been excluded. The number of plants (n) per treatment is shown.
Daily
Residual soil water (ml)
SE
θv
3/6-Day
7/14-Day
Cuttings
(n = 30)
Seedlings
(n =15)
Cuttings
(n = 30)
Seedlings
(n = 14)
Cuttings
(n = 28)
Seedlings
(n = 14)
61
13
0.01
44
17
0.01
195
23
0.04
57
17
0.01
161
33
0.04
11
21
0.002
WATER STRESS IN EUCALYPTUS CUTTINGS AND SEEDLINGS
potential is typical of many herbaceous (Ludlow 1980, Bradford and Hsiao 1982) and woody (Jarvis 1980, Sands and
Mulligan 1990) plants. The threshold at which water availability becomes dominant in determining stomatal conductance
depends on the species and the environment, and typically the
threshold and the gradient of the decrease is higher in plants
grown in controlled conditions than in plants grown in the field
(Jarvis 1980, Ludlow 1980).
At very low soil water availability (200 ml residual soil
water content), there were significant differences in plant
water potentials between treatments, but not between cuttings
and seedlings. This contrasts with Blake and Filho’s (1988)
results in which cuttings of E. grandis had higher midday
water potentials than seedlings after 2.5 days of drought. This
difference may be a consequence of the preconditioning treatments that we imposed before measurement at a constant water
content. Preconditioning treatments change the physiological
responses of plants to water stress (Hsiao 1973). Assessment
of the water relations of cuttings and seedlings from each
watering treatment at the same water content indicated that
preconditioning occurred in both cuttings and seedlings. Water
potentials were between 0.3 and 0.4 MPa greater in plants from
the 7/14-day treatment than in plants from the other treatments.
However, cuttings and seedlings differed in their response to
preconditioning. Decreased water potentials were accompanied by decreased transpiration and stomatal conductance in
seedlings, and by increased transpiration and stomatal conductance in cuttings.
Effectively preconditioned plants would be expected to endure water stress better than nonconditioned plants, and this
was manifested in the seedlings as a reduction in transpiration
and stomatal conductance at low water availability and a reduced residual soil water content at which plant death occurred
in the 7/14-day treatment. However, a similar trend was not
found in the cuttings, suggesting that, under field conditions,
cuttings would be less likely to survive extreme water stress.
The similarity of the responses of shoots of cuttings and
seedlings to reduced soil water availability throughout this
experiment suggests that the differences in resistance to water
stress are due to differences in the functional capacities of the
root systems of the two plant types, i.e., water uptake and
transport. Uptake is dependent on the water available in the soil
and the water potential gradient imposed by the shoot, but is
also determined by the physiological, morphological and anatomical characteristics of the root system (Teskey 1991). The
morphology and anatomy of the root system of cuttings are
fundamentally different from those of seedlings, as a result of
their adventitious origin. The consequences of these differences are poorly understood because it is difficult to elucidate
the consequences of altered morphology in a seedling root
system on anchorage, and uptake and transport of water and
nutrients (Torrey and Clarkson 1975, Fitter 1991, Harper et al.
1991). It is even more difficult to predict the consequences of
the differences in the root systems of seedlings and cuttings.
However, it is important to note that some individual cuttings
did resist water stress in a similar way to seedlings, suggesting
that cuttings can develop a functionally effective root system.
293
With further evaluation of the development of the root system
of cuttings, it should be possible to modify the root system
during propagation to produce cuttings that are as resistant to
water stress as seedlings.
Acknowledgments
Plant material was provided by Celulose Beira Industrial (CELBI),
S.A., Portugal. This work was conducted when the first author was a
recipient of an Australian Postgraduate Research Award.
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