Directory UMM :Data Elmu:jurnal:T:Tree Physiology:vol17.1997:

Tree Physiology 17, 407--414
© 1997 Heron Publishing----Victoria, Canada

Effects of cone-induction treatments on black spruce P
( icea mariana)
current-year needle development and gas exchange properties
RONALD F. SMITH1 and MICHAEL S. GREENWOOD2
1

Canadian Forest Service--Atlantic Forestry Centre, P.O. Box 4000, Fredericton, N.B. E3B 5P7, Canada

2

Department of Forest Ecosystem Science, University of Maine, Orono, ME 04469, USA

Received December 20, 1995

Summary Both drought and root pruning (RP) increased the
number of cones induced when black spruce (Picea mariana
(Mill.) B.S.P.) grafts were injected with gibberellins A4/7 (GA),
but their effects on predawn shoot water potential and currentyear needle development differed. Drought decreased predawn

shoot water potential (Ψpd), but only during the period when
irrigation was withheld, and it had no effect on the growth or
gas exchange properties of current-year needles. Conversely,
root pruning had little effect on Ψpd, but it resulted in trees with
smaller current-year needles that had lower nitrogen and chlorophyll concentrations and reduced rates of gas exchange up to
the later stages of shoot elongation compared with needles of
control trees. These findings are discussed in relation to potential effects on the development of induced cones in the following growth cycle.
Keywords: drought, GA4/7, photosynthesis, pollen-cone production, root pruning, seed-cone production, shoot water potential, stomatal conductance.

Introduction
Applying gibberellins A4 and A7 (GA), often in combination
with root pruning, drought, heat, and stem or branch girdling,
is commonly done to induce cone production in the Pinaceae
to expedite breeding (Ho 1988, 1991a, Greenwood et al.
1993), and for operational seed production (see reviews in
Bonnet-Masimbert 1987, Pharis et al. 1987, Philipson 1990).
The success of miniaturized or containerized orchards (Ross et
al. 1986, Ross 1989, Smith and Powell 1992, Sweet et al. 1992)
depends on a regular supply of high quality seed from GA-induced cones.
When properly formulated and applied, such induction

treatments are generally effective (Ross and Pharis 1981, Ross
and Bower 1989). However, needle loss following GA and
other induction treatments may occur (Ho 1991b, Ross 1991a,
Greenwood et al. 1993). Furthermore, although the GA-induced cones usually develop normally (Ross et al. 1980, Bonnet-Masimbert 1987, Bonnet-Masimbert and Zaerr 1987), they
are sometimes smaller than noninduced cones and have lower
seed yields (Puritch et al. 1979, Ross et al. 1980, Philipson
1987, Ross 1988, Philipson et al. 1990). The cause(s) of the

smaller cones has not been determined; however, a negative
correlation between number of cones produced and seed yield
per cone has been reported most often when trees produce
large cone crops.
Developing cones act as strong sinks for photosynthate and
nutrients (Dickmann and Kozlowski 1968, 1970). Competition
for nutrients may be a factor leading to the abortion of pollinated ovules and premature drop of conelets in pine (see
review by Owens 1991), but results for black spruce (Picea
mariana (Mill.) B.S.P.) are lacking. Similarly, the effects of
cone-induction treatments on needle development and gas
exchange and, concomitantly, the availability of photosynthate
to developing cones in black spruce, have not been quantified.

The objectives of this study were to: (1) quantify the effects
of injecting GA4/7 in combination with drought and root-pruning treatments on current-year needle morphology and nitrogen content, photosynthetic capacity, and gas-exchange
properties; and (2) determine whether these effects are causally related to successful cone induction.

Material and methods
Tree culture
Seven-year-old grafts from seven black spruce clones were
grown in 25-liter containers by J.D. Irving, Ltd. in their breeding hall in Sussex, N.B., Canada, then shipped to Fredericton
in January 1993. The phenological stages of developing current-year shoots were used to time the application of treatments. These stages were vegetative bud burst in the upper
one-third of the crown (VBB); early slow growth phase of
shoot elongation (ESE); rapid or exponential shoot elongation
phase (RSE); late slow growth phase of shoot elongation
(LSE); cessation of shoot elongation (CSE) (shoots visibly
lignified for approximately one-third to one-half their length
and all but a few needles at the apex reflexed and almost
perpendicular to the shoot axis); and completion of shoot
lignification (CSL) (Ho 1991a, Smith and Greenwood 1995).
The length of one lateral shoot on a 3-year-old branch was
measured twice weekly throughout the study periods in both
1993 and 1994.

408

SMITH AND GREENWOOD

In 1993, trees received 3.6 l of water and fertilizer daily
using a drip irrigation system. The trees received starter N,P,K
(11,41,8) at 50 ppm nitrogen (N) up to VBB, grower N,P,K
(20,8,20) at 100 ppm N during ESE and then at 200 ppm N
until CSL, and hardener N,P,K (8,20,30) at 35 ppm N, thereafter. In 1994, two changes were made: (1) trees were watered
every second day, and (2) N,P,K (20,8,20) was applied at
200 ppm N during ESE. Trees were grown in a greenhouse in
a 16-h photoperiod provided by Sylvania Lumalux GTE high
pressure sodium vapor lamps. The means (range) of temperatures were 22 (18--25) °C day and 18 (17--22) °C night up to
LSE and 30 (28--33) °C day and 20 (19--22) °C night, thereafter.
Treatments
In 1993, four ramets from each of seven clones received one of
four treatments: (1) control (C), (2) drought for 7 days from
March 19 to 26, 1993 (D), (3) stem injection of 10 mg GA4/7
(Zeneca Agro, Stoney Creek, Ontario) in 0.1 ml of 95% ethyl

alcohol on March 23, 1993 (GA), and (4) GA + D. The drought
was applied during the early slow growth phase of shoot
elongation (lateral shoots in the upper one third of the crown
were between 1 and 2 cm in length, except for Clone 3, in
which shoots averaged 4 to 5 cm in length). Treated grafts were
grown from March to May, hardened-off, and placed outside
in a shade area on June 15. All trees were moved to a greenhouse to thaw at 5 °C on January 19, 1994. After the plants had
thawed, the greenhouse day/night temperature was increased
to 15/10 °C. Conelet receptivity was completed by February
20, 1994.
On February 28, 1994 (before vegetative bud burst), two
ramets from each clone, the GA + D and D 1993 treatments,
were root pruned (RP) by making three vertical cuts plus
removing approximately 10 cm of roots from the bottom of the
rootball. On March 15, 1994, cones that had been induced in
1993 were counted and the root-pruned trees were given a stem
injection of 10 mg GA4/7. Ramets in the C and GA 1993
treatments were retained as controls in 1994. On June 29,
1994, after shoots had lignified, trees were placed in a cooler
at 5 ± 2 °C until September 6 when they were returned to the

greenhouse, flushed, and the cones induced in 1994 counted.
Needle morphology and gas exchange
Morphology and rates of gas exchange of current-year needles
were assessed for second-order lateral shoots from 3-year-old
branches from shortly after vegetative bud burst to the time
when elongating shoots became lignified. Gas exchange was
measured between 0800 and 1200 h with an LI-6200 portable
photosynthesis system (Li-Cor Inc., Lincoln, NE) equipped
with a 250-ml cuvette and calibrated before each set of measurements against a certified CO2 source (500 ppm). Before
commencing measurements, shoots were inserted in the cuvette and acclimated for 30 to 45 s to a Sylvania 90-W capsylite
halogen light providing a mean (± SE) photosynthetically
active radiation (PAR) of 1092 ± 40 and 1079 ± 20 µmol
m −2 s −1, for 1993 and 1994, respectively. Ambient CO2 was

467 ± 3 and 412 ± 3 ppm in 1993 and 1994, respectively. Two
shoots per ramet were measured on each sampling date. Measurements were made successively on shoots in comparable
positions to ensure that starting CO2 concentration, chamber
temperature, relative humidity, and light did not change significantly between measurements. Except for respiring shoots
that had elongated less than 2 cm, PAR, relative humidity, and
temperature within the cuvette did not vary by more than 20%

between successive measurements for a given ramet and were
not significantly different at α = 0.05 in paired t-tests
(Snedecor and Cochrane 1980). Net photosynthesis (Pn) and
stomatal conductance (gs) were expressed per unit of needle
surface area as µmol m −2 s −1 and mol m −2 s −1, respectively.
Total shoot length, numbers of needles, and their fresh and dry
(48 h at 65 °C) weights were determined for one of the shoots
per ramet used for gas-exchange measurements. One-sided
projected surface area (SA) of a random 50-needle sample was
measured with a Delta-T area meter (Delta-T Devices Ltd.,
Cambridge, England). The leaf dry weight/leaf area ratio (W,
gDW mm −2) was determined as described by Oren et al. (1986).
Total nitrogen concentration (mg gDW−1) was determined by a
modified micro-Kjeldahl method (Technicon Industrial
Method No. 334-74W/B+) (Technicon Instruments Corp., Tarrytown, NY) using a Technicon BD40 acid block digester.
Chlorophyll of needles from the second shoot per ramet
used for gas-exchange measurements was extracted by a modified dimethylsulfoxide (DMSO) method (Hiscox and Israelstam 1979, Greenwood et al. 1989) and absorbance was
measured with a Technicon AA II autoanalyzer equipped with
wavelength specific filters of 666 and 648 nm. Absorbancy
values were converted to concentrations (mg gDW−1) based on

the extinction coefficients of chlorophylls a and b from spinach
(Sigma Chemical Co., St. Louis, MO). Chlorophyll estimates
were checked with a Spectronic 1201 spectrophotometer (Milton Roy Co., Rochester, NY) in 1993 and a Phillips PU 8800
UV/VIS spectrophotometer (Pye Unicam Ltd., Cambridge,
England) in 1994. The R2 values were 0.863 (P < 0.001) and
0.926 (P < 0.001) for 1993 and 1994, respectively (Smith
1995).
Water status measurements
Predawn shoot water potential (Ψpd, MPa) was measured with
a pressure chamber (PMS Instrument Co., Corvallis, OR). The
first reading was taken on 1-year-old shoots because the current-year shoots had not developed sufficiently for a reliable
reading. Subsequent readings were taken on current-year
shoots. The volumetric field capacity (FC) of the containers
was determined as the total pore space less the drainable pore
space (see Whitcomb 1988) measured with a TRASE unit (Soil
Moisture Corp., Santa Barbara, CA).
Data analyses
All data were tested for normality, and transformations performed as required. Analyses of variance were performed with
the SAS software package (SAS Institute Inc., Cary, NC,
1990).

TREE PHYSIOLOGY VOLUME 17, 1997

CONE INDUCTION TREATMENTS ON BLACK SPRUCE

Results
Cone production
The GA + D-treated trees produced significantly (P < 0.01)
more seed cones than the C, D-, and GA-treated trees (Table 1).
All of the 162 seed cones induced on the GA + D-treated trees
proliferated (see Caron and Powell 1991). In 1994, the GA +
RP-treated trees produced more seed and pollen cones than the
control trees, but the differences were only significant
(P < 0.01) for seed cones (Table 1). Four of 13 control trees
produced seed cones, but only one ramet produced pollen
cones. In contrast to the 1993 experiment, only four of the
cones initiated during the 1994 treatments proliferated, and all
four cones were on one tree.
Clonal differences in cone production responses to the treatments were evident within a year, but the clones that failed to
produce cones in response to GA + D in 1993 were not the

clones that exhibited a poor response to GA + RP in 1994. The
number of cones produced in response to the 1994 treatments
was not affected by the GA treatment in March 1993. The
ortets ranged from 17 to 64 years of age, but neither responsiveness to treatment nor degree of cone proliferation in response to the 1993 treatments was related to ortet age.
Tree development and shoot elongation
In both 1993 and 1994, the treatments did not significantly
affect the timing of shoot development or final shoot length.
Similarly, the 1993 treatments had no effect on growth in 1994.
Although asynchronous with natural vegetative bud development, the sequence of vegetative bud development appeared
normal in both years (Smith 1995).
Correlations between cone production and shoot water
potential and needle water content

409

been subjected to drought, compared with pre-drought values.
This difference was probably due in part to the difference in
Ψpd between current-year and 1-year-old shoots. Predawn
shoot water potentials were significantly (P < 0.001) lower in
drought-treated trees than in control trees. Although trees exhibiting the lowest Ψpd produced the most cones, only trees

receiving both GA and drought produced cones. Shoot water
potentials of drought-treated trees recovered to control values
within 24 h of resuming irrigation. There were no significant
differences in needle water content between treatments. The
dry weight/fresh weight ratio of developing needles generally
increased up to CSE (Smith 1995), but neither needle fresh
weight nor needle dry weight was correlated with Ψpd or
successful cone induction in either year.
In 1993, mean (± SE) field capacity for all pots was 44.6 ±
2.0% and ranged from 35.8 to 56.7%. In 1993, container water
contents generally remained above 95% of field capacity
(Smith 1995), except during the drought period. By the end of
the drought period, container water contents in the D and GA
+ D treatments were reduced to 58.6 ± 10.2 and 60.3 ± 9.2%
of field capacity, respectively, and there were significant
(P < 0.001) differences among clones. In 1994, container
water content, measured 1 hour before irrigation, decreased
from 88% of field capacity at the time of vegetative bud burst
to 62% of field capacity at the time when shoot elongation
stopped, but remained constant thereafter.
Correlations between container water content and Ψpd of
trees subjected to 3 and 7 days of drought were R = −0.6204
(P < 0.0179) and R = −0.7304 (P < 0.0030), respectively. The
corresponding correlations for irrigated trees were also negative, but they were not significant: R = −0.3269 (P = 0.2540)
and R = −0.3405 (P = 0.2236). Gibberellin injections had no
effect on the rate of water use. Container water content was
higher for root-pruned trees than for control trees, but the
differences were not significant.

In 1993, Ψpd values at the end of the drought period were
generally lower in all trees, including the trees that had not
Needle development
Table 1. Mean (SE) number of seed cones and pollen cones per treated
tree and mean (SE) predawn shoot water potential (Ψpd, MPa) of
treated trees. The 1993 treatments were: C = control, GA = stem
injection with 10 mg GA4/7, D = drought (irrigation withheld for
7 days), and GA + D; and the 1994 treatments were: C = control and
GA + RP = stem injection with 10 mg GA 4/7 plus root pruning (RP).
Within a year, means followed by different letters are significant at
P < 0.05.
Treatment

Ψpd

No. of seed
cones per tree

No. of pollen
cones per tree

1993 Experiment
C
GA
D
GA + D

−0.56 (0.07) a
−0.73 (0.03) a
−1.03 (0.21) b
−0.98 (0.24) b

0.0 (--) a
0.3 (0.3) a
0.0 (--) a
23.4 (10.9) b

-----

1.9 (0.9) a
21.6 (7.1) b

3.6 (3.6) a
7.0 (3.2) a

1994 Experiment
C
GA + RP

In both 1993 and 1994, the mean surface area of developing
current-year needles increased little prior to the late phase of
slow shoot elongation, but steadily thereafter, whereas needle
dry weight increased gradually throughout the sampling period (Figure 1, Smith 1995). None of the treatments had a
significant effect on needle characteristics in 1993. Needle
weight, surface area, leaf dry weight/leaf area ratio, nitrogen
content and chlorophyll concentration were positively correlated with each other in both years (Smith 1995). In 1994,
increases in needle dry weight and surface area with successive
collections were less for GA + RP-treated trees than for control
trees, resulting in smaller needles with a higher leaf dry
weight/leaf area ratio in the treated trees (Figure 1).
In both years, total N content per needle and total chlorophyll concentration (Figure 2B, C, Smith 1995) increased from
ESE to CSE, whereas percent N (Figure 2A) and the N/chlorophyll ratio decreased (Table 2). In 1994, total N content and
total chlorophyll concentration of needles were lower in GA +
RP trees than in C trees (Figures 2B and 2C). The N/chloro-

TREE PHYSIOLOGY ON-LINE at http://www.heronpublishing.com

410

SMITH AND GREENWOOD

Figure 1. Means (± 1 SE) of (A) needle dry weight, (B) needle surface
area (SA), and (C) needle dry weight/needle area ratio (W) for control
trees (d); and trees receiving GA4/7 plus root pruning (j). ESE = early
phase of slow shoot elongation, e-RSE = early rapid phase of shoot
elongation, m-RSE = mid rapid phase of shoot elongation, LSE = late
slow phase of shoot elongation, and CSE = cessation of shoot elongation.

Figure 2. Means (± 1 SE) of (A) needle nitrogen concentration (percent dry weight), (B) needle nitrogen content (µg per needle), and (C)
total chlorophyll concentration (mg gDW−1) for control trees (d) and
trees receiving GA4/7 plus root pruning (j). See caption to Figure 1
for definition of abbreviations.

Table 2. Comparison of means (SE) of nitrogen/chlorophyll ratios for cone-bearing (F) and non-cone-bearing (NF) grafts in 1993 and 1994, and
between drought-treated (D) and control (C), and between root-pruned (GA + RP) and control (C) trees at different stages of shoot development.
Treatment means within collections followed by different letters are significant at P < 0.05. ESE = early phase of slow shoot elongation, RSE =
rapid shoot elongation phase, LSE = late phase of slow shoot elongation, CSE = cessation of shoot elongation, and CSL = completion of shoot
lignification.
Stage of shoot development
1993 Experiment
F
NF
C
D

ESE
40.2(4.7) a
36.4(2.0) a
36.4(1.9) a
34.0(2.2) a

RSE
11.2(0.5) a
10.7
9.9(0.6) a
9.0(0.4) a

CSE
5.4(0.3) a
4.7(0.3) a
5.0(0.2) a
4.7(0.2) a

CSL
6.1(0.5) a
5.7(0.5) a
6.7(0.5) b
5.3(0.2) a

1994 Experiment
F
NF
C
GA + RP

ESE
22.9(1.0) a
24.9(1.4) a
23.1(1.1) a
25.7(1.4) a

early-RSE
18.3(1.7) a
17.4(1.4) a
15.2(1.2) a
20.9(1.6) b

mid-RSE
9.5(0.7) a
9.7(0.5) a
9.5(0.5) a
9.9(0.6) a

LSE
8.2(1.4) a
7.1(0.5) a
6.2(0.8) a
8.7(1.1) b

TREE PHYSIOLOGY VOLUME 17, 1997

CSE
5.5(0.3) a
5.3(0.5) a
5.2(0.5) a
5.3(0.3) a

CONE INDUCTION TREATMENTS ON BLACK SPRUCE

411

Figure 4. Means (± 1 SE) of stomatal conductance for control (d) trees
and trees receiving GA4/7 (j) plus root pruning. See caption to Figure
1 for definition of abbreviations.

parameters did not differ between cone-producing and noncone-producing trees in either year.
Gas exchange measurements

Figure 3. Means (± 1 SE) of (A) net photosynthesis per gram dry
weight, (B) net photosynthesis per mg total chlorophyll, and (C) net
photosynthesis on a surface area basis for control trees ( d); and trees
receiving GA4/7 plus root pruning (j). See caption to Figure 1 for
definition of abbreviations.

phyll ratio was also lower in GA + RP trees than in C trees but
the differences were only significant (P < 0.05) for collections
made during early RSE and LSE (Table 2). Needle growth

Net photosynthesis was lower for GA + RP trees than for C
trees from ESE to mid-RSE (Figure 3). The standard errors of
the gas exchange measurements were large during the phase of
slow shoot elongation. Net photosynthesis and stomatal conductance were lower for drought-treated trees than for control
trees during ESE and were negative during the later stages of
the drought period; however gas exchange returned to control
values within 24 h of watering the drought-treated trees.
The GA + RP trees exhibited significantly lower net photosynthesis (Figure 3) and stomatal conductance (Figure 4) than
control trees for all clones. In both 1993 and 1994, gas exchange measurements differed significantly among shoot development stages (Table 3).

Table 3. Summary of mean squares and probabilities (P) for gas exchange measurements: Pn,DW = net photosynthesis on a dry weight basis,
P n,area = net photosynthesis on a surface area basis, P n,chl = net photosynthesis on a chlorophyll basis, and gs = stomatal conductance, CD =
collection date, ns = not significant. Values represent analyses on log transformed data.
Treatment

df

P n,DW

P n,area

P n,chl

gs

1993 Experiment
CD (C)
Treatment (T)
C×T
Error

3
3
9
138

19.71 (0.001)
0.68 ns
0.25 ns
0.34

35.25 (0.001)
0.9 ns
0.09 ns
0.64

83.27 (0.001)
0.54 ns
0.28 ns
0.38

9.22 (0.001)
0.04 ns
0.51 ns
0.34

1994 Experiment
CD (C)
Treatment (T)
C×T
Error

4
1
4
200

1.89 (0.002)
5.06 (0.001)
0.64 ns
0.42

1.84 (0.003)
4.99 (0.001)
0.96 (0.073)
0.44

12.78 (0.001)
2.93 (0.005)
0.39 ns
0.37

5.38 (0.001)
8.55 (0.001)
0.69 (0.082)
0.33

TREE PHYSIOLOGY ON-LINE at http://www.heronpublishing.com

412

SMITH AND GREENWOOD

Discussion
In 1993, the drought treatment had no persistent effect on
needle development or gas exchange properties. However,
only trees receiving both the GA and drought treatments produced cones. Drought may reduce oxidative metabolism of
exogenously applied GA, thereby increasing the less polar or
florigenic forms (Chalupka et al. 1982, Dunberg et al. 1983).
Although proliferated cones comprise only a small percentage of the total numbers of cones produced under natural
conditions (Caron and Powell 1991), all of the cones induced
in 1993 proliferated. Increased rates of cone proliferation in
response to stresses imposed during cone induction is common
(Ross and Pharis 1987); however, this is the first report of
100% of induced cones being proliferated. Although seedcone development in response to the GA + D treatment in 1993
was abnormal, the elongating vegetative shoots and differentiating vegetative primordia developed normally (Smith 1995).
Unfortunately, the GA and root pruning treatments were not
tested separately in 1994; however, their combination resulted
in a significant increase in cone production compared with the
untreated controls. Several modes of action by which root
pruning increases the efficacy of exogenously applied GAs in
inducing cone production have been proposed: (1) bud development may be delayed to a time when warm and dry weather
conditions prevail and thus favor buds differentiating reproductively; (2) the numbers of buds that are receptive to GA
may be increased (Owens 1987, Owens et al. 1992); or (3)
cytokinin export from the roots may be reduced, thereby either
slowing cell division within developing buds and increasing
their period of receptivity to both endogenous and exogenously applied GA4/7, or relieving the bud of the presence of
cytokinins, if inhibitory to cone production (Smith and Greenwood 1995).
Successful cone induction was not correlated with any
measurable effects on shoot elongation. The failure of the D
and RP treatments to reduce shoot elongation is contrary to the
results of Webber et al. (1985), but similar to the findings of
Hall (1988), Ross (1991b), and Smith and Greenwood (1995).
Cone induction treatments may have a greater effect on the
elongation of leaders and vigorous terminal shoots than the
less vigorous laterals measured in this study (Philipson et al.
1990).
In 1993, although drought increased Ψpd, the effects did not
persist when the trees were rewatered (cf. Ross 1991a). Root
pruning had no significant effect on Ψpd. This observation is
contrary to findings in other studies (Ross et al. 1985, Webber
et al. 1985), but supports the hypothesis that root pruning does
not exert its effects by causing plant water stress, i.e., it does
not simulate drought (Ross 1991a) even though both root
pruning and drought treatments increase the cone-inducing
effectiveness of GA.
In both 1993 and 1994, total N content and total chlorophyll
concentration of needles were positively correlated and increased until lateral shoot elongation ceased (cf. Oku et al.
1977, Kozlowski et al. 1991). Drought had no effect on needle
chlorophyll concentration; a similar finding has been reported
for Picea abies (L.) Karst. (Cornic 1987). In 1994, current-year

needles from GA + RP trees had a lower concentration of total
chlorophyll and a lower total N content than control trees
(Figure 2). Similarly, the total chlorophyll concentration of
current-year needles of field-grown black spruce was reduced
following six foliar applications of GA4/7 (R. Smith, unpublished observations). Although synthesis of the GA precursor
ent-kaurene (Graebe and Ropers 1978, Moore 1989) has been
correlated with chlorophyll concentration (Moore and Coolbaugh 1991), we conclude that the total chlorophyll concentration of current-year needles cannot be used as a general
response indicator of successful cone induction in black
spruce.
The reduction in N content of needles following the D and
GA + RP treatments contrasts with many studies showing that
N contents of shoots, needles, and buds are increased following drought (Cyr et al. 1990, Beyers et al. 1992) or successful
cone induction, or both (Barnes and Bengston 1968, Ebell and
McMullin 1970, Daoudi et al. 1994). The decrease in percent
total N (dry weight basis) of developing needles during the
period of shoot elongation was similar to that found for Picea
sitchensis (Bong.) Carrière (Lewandowska and Jarvis 1977)
and may have confounded the effects of treatments on needle
N content.
Current-year needles of trees receiving the GA + RP treatment in 1994 were smaller than those of control trees. These
smaller needles may have a reduced capacity to provide photosynthate to developing cones in the following growth cycle,
which would reduce the size of the previously initiated cone
scales and would also explain why cones produced in response
to GA plus an adjunct stress treatment are sometimes smaller
than natural cones. Part of the reduction in tree growth following a good cone-bearing year may be the result of lower needle
areas in response to ‘‘stress,’’ i.e., dry weather, rather than the
presence of female cones per se (Dick et al. 1990).

Conclusions
Both drought and root pruning, when applied within 10 days
of vegetative bud burst, acted synergistically with GA to increase cone production, but these treatments affect currentyear needle development and gas exchange properties
differently. Drought-treated trees exhibited more negative predawn pressure potentials and reduced rates of gas exchange
than control trees, but these effects did not persist after trees
were rewatered. There were no significant differences in needle size, weight or needle N or chlorophyll content between
drought-treated and control trees. Conversely, when compared
to control trees, current-year needles of GA + RP trees were
smaller with lower N and chlorophyll contents, and exhibited
lower net photosynthesis up to the latter stages of shoot elongation. We postulate that these smaller needles have a reduced
capacity to provide photosynthate to the cones that mature in
the following year.
Acknowledgments
The authors acknowledge Greg Adams and Hart Kunze of J.D. Irving,
Ltd., for providing the study trees and technical assistance. The assis-

TREE PHYSIOLOGY VOLUME 17, 1997

CONE INDUCTION TREATMENTS ON BLACK SPRUCE
tance of Cindy Henderson in developing protocols and technical expertise in using the Technicon for chlorophyll analyses is greatly
appreciated. We also thank S.I. Cameron, C.H.A. Little, Y.S. Park and
G. Powell for reviews of an earlier draft of this manuscript, and D.
Perry for word processing. Finally, we wish to acknowledge Laurie
Yeates for exemplary technical assistance throughout the project.

References
Barnes, R.L. and G.W. Bengston. 1968. Effects of fertilization, irrigation, and cover cropping on flowering and on nitrogen and soluble
sugar composition of slash pine. For. Sci. 14:172--180.
Beyers, J.L., G.H. Reichers and P.J. Temple. 1992. Effects of longterm ozone exposure and drought on the photosynthetic capacity of
ponderosa pine (Pinus ponderosa Laws.). New Phytol. 122:81--90.
Bonnet-Masimbert, M. 1987. Floral induction in conifers: a review of
available techniques. For. Ecol. Manage. 19:135--146.
Bonnet-Masimbert, M. and J.B. Zaerr. 1987. The role of plant growth
regulators in promotion of flowering. Plant Growth Regul. 6:13--35.
Caron, G.E. and G.R. Powell. 1991. Proliferated seed cones and pollen
cones in young black spruce. Trees 5:65--74.
Chalupka, W., M. Giertych and J. Kopcewicz. 1982. Effects of polyethylene covers, a flower inducing treatment on the content of
endogenous gibberellin-like substances in grafts of Norway spruce.
Physiol. Plant. 54:79--82.
Cornic, G. 1987. Interaction between sublethal pollution by sulphur
dioxide and drought stress: The effect on photosynthetic capacity.
Physiol. Plant. 71:115--119.
Cyr, D.R., G.F. Buxton, D.P. Webb and E.B. Dumbroff. 1990. Accumulation of free amino acids in the shoots and roots of three
northern conifers during drought. Tree Physiol. 6:293--303.
Daoudi, E.H., P. Doumas and M. Bonnet-Masimbert. 1994. Changes
in amino acids and polyamines in shoots and buds of Douglas-fir
trees induced to flower by nitrogen and gibberellin treatments. Can.
J. For. Res. 24:1854--1863.
Dick, J. McP., R.B.B. Leakey and P.G. Jarvis. 1990. Influence of
female cones on the vegetative growth of Pinus contorta trees. Tree
Physiol. 6:151--163.
Dickmann, D.I. and T.T. Kozlowski. 1968. Mobilization by Pinus
resinosa cones and shoots of 14C-photosynthate from needles of
different ages. Am. J. Bot. 55:900--906.
Dickmann, D.I. and T.T. Kozlowski. 1970. Mobilization and incorporation of photo-assimilated 14C by growing vegetative and reproductive tissues of adult Pinus resinosa Ait. trees. Plant Physiol.
45:284--288.
Dunberg, A., G. Malmberg, T. Sassa and R.P. Pharis. 1983. Metabolism of tritiated gibberellins A4, and A9 in Norway spruce, Picea
abies (L.) Karst. Plant Physiol. 71:257--262.
Ebell, L.F. and E.E. McMullin. 1970. Nitrogenous substances associated with differential cone production responses of Douglas-fir to
ammonium nitrate fertilization. Can. J. Bot. 48:2169--2177.
Graebe, J.E. and H.J. Ropers. 1978. Gibberellins. In Phytohormones
and Related Compounds----A Comprehensive Treatise, Vol. 1. Eds.
D.S. Letham, P.B. Goodwin and T.J.V. Higgins. Elsevier, Holland,
Chapter 3, 641 p.
Greenwood, M.S., C.A. Hopper and K.W. Hutchison. 1989. Maturation in larch. I. Effects of age on shoot growth, foliar characteristics,
and DNA methylation. Plant Physiol. 90:406--412.
Greenwood, M.S., G. Adams and S. Kempton. 1993. Using recent
advances in the control of conifer reproductive development to
increase genetic gain. In Proc. 24th Mtg. Can. Tree Improv. Assoc.,
Part 2. Ed. J. Lavereau. Fredericton, N.B., pp 19--26.

413

Hall, P.J. 1988. Promotion of flowering in black spruce using gibberellins. Silvae Genet. 37: 3--4.
Hiscox, J.D. and G.F. Israelstam. 1979. A method for the extraction of
chlorophyll from leaf tissue without maceration. Can. J. Bot.
57:1332--1334.
Ho, R.H. 1988. Gibberellin A4/7 enhances seed-cone production in
field-grown black spruce. Can J. For. Res. 18:139--142.
Ho, R.H. 1991a. Timing of gibberellin A4/7 application for cone
production in potted black spruce grafts. Can. J. For. Res. 21:1137-1140.
Ho, R.H. 1991b. Promotion of cone production in potted black-spruce
grafts, using gibberellins, heat-treatment and root-pruning. For.
Ecol. Manage. 40:243--260.
Kozlowski, T.T., P.J. Kramer and S.G. Pallardy. 1991. The physiological ecology of woody plants. Academic Press, New York, 657 p.
Lewandowska, M. and P.G. Jarvis. 1977. Changes in chlorophyll and
carotenoid content, specific leaf area and dry weight fraction in
sitka spruce, in response to shading and season. New Phytol.
79:247--256.
Moore, T.C. 1989. Biochemistry and physiology of plant hormones.
Springer Verlag, New York, 330 p.
Moore, T.C. and R.C. Coolbaugh. 1991. Correlations between apparent rates of ent-kaurene biosynthesis and parameters of growth and
development in Pisum sativum. In Gibberellins. Eds. N. Takahashi,
B.O. Phinney and J. Macmillan. Springer-Verlag, New York, pp
188--198.
Oku, T., S. Furuta, K. Shimado, Y. Kobayashi, T. Ogawa, Y. Indie and
K. Shibata. 1977. Development of the photosynthetic apparatus in
spruce leaves. In Photosynthetic Organelles: Structure and Function. Jap. Plant Physiol. Centre, Acad. Publ., Nakanishi Print Co.,
Kyoto, Japan, pp 437--444.
Oren, R., E.-D. Schulze, R. Maryssek and R. Zimmermann. 1986.
Estimating photosynthetic rate and annual carbon gain in conifers
from specific leaf weight and leaf biomass. Oecologia 70:187--193.
Owens, J.N. 1987. Development of Douglas-fir apices under natural
and cone-inducing conditions. For. Ecol. Manage. 19:85--97.
Owens, J.N. 1991. Measuring growth and development of reproductive structures. In Techniques and Approaches in Forest Tree Ecophysiology. Eds. J.P. Lassoie and T.M. Hinckley. CRC Press, Boca
Raton, FL, pp 423--452.
Owens, J.N., J.J. Philipson and D.L.S. Harrison. 1992. The effects of
the duration and timing of drought plus heat plus gibberellin A 4/7 on
apical meristem development and coning in Sitka spruce (Picea
sitchensis (Bong.) Carr.). New Phytol. 122:515--528.
Pharis, R.P., J.E. Webber and S.D. Ross. 1987. The promotion of
flowering in forest trees by gibberellin A 4/7 treatments: a review of
the possible mechanisms. For. Ecol. Manage. 19:65--84.
Philipson, J.J. 1987. Promotion of cone and seed production by gibberellin A4/7 and distribution of pollen and seed cones on Sitka
spruce grafts in a clone bank. For. Ecol. Manage. 19:147--154.
Philipson, J.J. 1990. Prospects for enhancing flowering of conifers and
broadleaves of potential silvicultural importance in Britain. Forestry 63:223--240.
Philipson, J.J., J.N. Owens and M.A. O’Donnell. 1990. Production
and development of seed and pollen in grafts of Picea sitchensis
(Bong.) Carr. treated with gibberellin A 4/7 to induce coning and the
effect of forcing treatments. New Phytol. 116:695--705.
Puritch, G.S., E.E. McMullin, M.D. Meager and C.S. Simmons. 1979.
Hormonal enhancement of cone production in Douglas-fir grafts
and seedlings. Can. J. For. Res. 9:193--200.
Ross, S.D. 1988. Pre- and post-pollination polyhouse environment
effects on pollen and seed development in potted Picea engelmannii
grafts. Can. J. For. Res. 18:623--627.

TREE PHYSIOLOGY ON-LINE at http://www.heronpublishing.com

414

SMITH AND GREENWOOD

Ross, S.D. 1989. Long term cone production and growth responses to
crown management and gibberellin A4/7 treatment in a young western hemlock seed orchard. New For. 3:235--245.
Ross, S.D. 1991a. Effect of heat sums and of heat applied separately
to shoots and roots on flowering in potted Picea glauca grafts. Can.
J. For. Res. 21:672--679.
Ross, S.D. 1991b. Promotion of flowering in potted white spruce
grafts by root pruning: its relationship to drought and shoot elongation. Can. J. For. Res. 21:680--685.
Ross, S.D. and R.P. Pharis. 1981. Recent developments in enhancement of seed production in conifers. In Seed Orchards and Strategies for Tree Improvement, Part 2. Eds. D.F.W. Pollard, D.G.
Edwards and C.W. Yeatman. Proc. 18th Mtg. Can. Tree Improv.
Assoc., Duncan, B.C. pp 26--38.
Ross, S.D. and R.P. Pharis. 1987. Control of sex expression in conifers.
Plant Growth Regul. 6:37--60.
Ross, S.D. and R.C. Bower. 1989. Cost-effective promotion of flowering in a Douglas-fir seed orchard by girdling and pulsed stem
injection of gibberellin A4/7. Silvae Genet. 38:189--194.
Ross, S.D., R.P. Pharis and J.C. Heaman. 1980. Promotion of cone and
seed production in grafted and seedling Douglas-fir seed orchards
by application of gibberellin A4/7 mixture. Can. J. For. Res. 10:464-469.
Ross, S.D., J.E. Webber, R.P. Pharis and J.N. Owens. 1985. Interaction
between gibberellin A4/7 and root-pruning on the reproductive and
vegetative process in Douglas-fir. I. Effects on flowering. Can. J.
For. Res. 15:341--347.

Ross, S.D., A.M. Eastham and R.C. Bower. 1986. Potential for indoorpotted seed orchards. In Proc. Conifer Tree Seed in the Inland
Mountain West Symp., Missoula, Montana. Ed. R. Shearer. USDA
For. Serv. Intermountain Res. Stn., Gen Tech. Rep. INT-203, pp
180--186.
Smith, R.F. 1995. Effects of cone induction treatments on seed- and
pollen-cone production, bud anatomy, and needle development in
black spruce (Picea mariana (Mill.) B.S.P.). Ph.D. Thesis, Univ.
Maine, Orono ME, 89 p.
Smith, R.F. and G.R. Powell. 1992. Is there a place for alternatives to
conventional seed orchards in the Maritimes? Can. For. Serv., Atlantic R & D Tech. Note No. 4, 3 p.
Smith, R.F. and M.S. Greenwood. 1995. Effects of gibberellin A 4/7,
root-pruning, and cytokinins on seed- and pollen-cone production
in black spruce (Picea mariana (Mill.) B.S.P.). Tree Physiol.
15:457--466.
Snedecor, G.W. and W.G. Cochrane. 1980. Statistical methods. Iowa
State University Press, Ames IA, 507 p.
Sweet, G.B., R.L. Dickson, B.D. Donaldson and H. Litchwark. 1992.
Controlled pollination without isolation----a new approach to the
management of radiata pine seed orchards. Silvae Genet. 41:95--99.
Webber, J.E., S.D. Ross, R.P. Pharis and J.N. Owens. 1985. Interaction
between gibberellin A4/7 and root-pruning on the reproductive and
vegetative process in Douglas-fir. II. Effects on shoot elongation
and its relationship to flowering. Can. J. For. Res. 15:348--353.
Whitcomb, C.E. 1988. Plant production in containers. Lacebark Publications Inc., Stillwater OK, 633 p.

TREE PHYSIOLOGY VOLUME 17, 1997