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

Tree Physiology 17, 221--230
© 1997 Heron Publishing----Victoria, Canada

Effect of mineral nutrient content on oxygen exchange and
chlorophyll a fluorescence in needles of Norway spruce
MARTIN STRAND
Department of Forest Genetics and Plant Physiology, The Swedish University of Agricultural Sciences, S-901 83 Umeå, Sweden

Received June 27, 1996

Summary Photosynthetic O2 evolution at high irradiances
(approximately 600--1000 µmol m −2 s −1) and O2 uptake in
darkness were measured in needles of control, irrigated and
irrigated-fertilized trees of Norway spruce (Picea abies (L.)
Karst.). Measurements were made at 20 °C and at high CO2
concentrations. The results suggest that, at given times of the
year, a major part of the variation in gross photosynthesis of
current-year and one-year-old needles across treatments is
associated with differences in needle N content. Furthermore,
the rate of O2 uptake measured after 5 or 10 min in darkness
was positively correlated with both the preceding rate of gross

O2 evolution and the N content in fully expanded current-year
needles. Measurements of chlorophyll a fluorescence, taken
simultaneously with measurements of O2 evolution in currentyear sun needles, showed that Stern-Volmer quenching of
minimum fluorescence and the ratio of variable to maximum
fluorescence in the dark- and light-adapted state were strongly
correlated with the gross rate of O2 evolution. This suggests
that the increased rate of gross photosynthesis in needles of
irrigated-fertilized trees was associated with adjustments in the
thermal energy dissipation within photosystem II.
Keywords: dark respiration, fertilization, fluorescence
quenching, leaf nitrogen, photosynthesis, Picea abies.

Introduction
A strong positive correlation usually exists between the lightsaturated rate of CO2 assimilation (measured at near optimum
temperatures, relatively high humidities and CO2 concentrations typical of normal air) and foliar N content (Field and
Mooney 1986, Evans 1989), because the majority of foliar N
is associated with proteins participating in photosynthetic reactions (Evans 1989, Evans and Seemann 1989). However,
there is variation in this relationship among different species,
especially when photosynthetic rates and foliar N contents are
expressed on a leaf area basis (Evans 1989). The relationship

between photosynthetic capacity and foliar N content in the
field is less well documented for evergreen conifers than for
other higher plants. Vapaavuori et al. (1995) found a significant
correlation between the light-saturated rate of CO2 assimilation and foliar N content (both expressed on a dry mass basis)

in one-year-old shoots of Scots pine (Pinus sylvestris L.)
collected from mid-June to mid-August from four sites with
different fertility. Smolander and Oker-Blom (1989) also
found that the light-saturated rate of CO2 assimilation was
correlated with the foliar N content in one-year-old needles of
Scots pine in June. However, fertilization of conifers in the
field may have little or no effect on the rate of net photosynthesis (Sheriff et al. 1986, Teskey et al. 1994a), which may be
a result of nutrient imbalances induced by the treatments
(Teskey et al. 1994b). Imbalances between nutrient elements
in the foliage are probably less common in field experiments
in which a complete nutrient solution is supplied with the
irrigation water. In one such experiment, one-year-old shoots
of irrigated-fertilized (IL) trees of Scots pine had an in situ rate
of CO2 assimilation approximately 20% greater than corresponding shoots of irrigated (I) trees over a wide range of
temperatures and incident irradiances (Linder and Troeng

1980). However, shoots of IL trees of Pinus radiata D. Don
had a higher rate of CO2 assimilation than shoots of I trees only
when stomatal conductances were high (Thompson and
Wheeler 1992).
Several studies have shown that the photosynthetic rate at
any intercellular partial pressure of CO2 increases with increasing foliar N content (e.g., Evans and Terashima 1988, Sage
et al. 1990, Makino et al. 1994, Tan and Hogan 1995). According to the photosynthetic model of Farquhar and von Caemmerer (1982), the photosynthetic rate at low intercellular
partial pressures of CO2 is limited by Rubisco activity, and the
rate at higher intercellular partial pressures of CO2 is limited
by electron transport capacity. However, photosynthesis under
saturating CO2 conditions may also be limited by the capacity
of starch and sucrose synthesis to regenerate orthophosphate
for photophosphorylation (Sharkey 1985), especially in leaves
with high N contents (Sage et al. 1990, Makino et al. 1994). At
high partial pressures of CO2, the rate of O2 evolution appeared
to be equivalent to the rate of CO2 assimilation in leaves of
spinach (Spinacia oleracea L.) with varying N contents (Evans
and Terashima 1988).
Measurements of O2 exchange have recently been used to
investigate seasonal changes in photosynthesis of Norway

spruce (Picea abies (L.) Karst.) (Strand 1995, Strand and
Lundmark 1995). The CO2-saturated rate of gross O2 evolution

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STRAND

at high irradiances in current-year and one-year-old needles
from the upper part of the canopy of IL trees was generally
higher than in corresponding needles of control (C) trees.
Furthermore, measurements of chlorophyll a fluorescence
showed that treatment-related differences in the rate of gross
O2 evolution were accompanied by a higher maximum photochemical efficiency of photosystem II (FV /FM ) in needles of IL
trees than in those of C trees. In this long-term field experiment, the mineral nutrient content of foliage was extensively
investigated (Linder 1995). The N content was markedly
higher in needles from the fourth whorl of IL trees than in
corresponding needles of C trees, indicating that the CO2-saturated rate of photosynthesis at high irradiances may be correlated with N content. To examine this hypothesis more closely,
the content of mineral nutrients was analyzed in needles for
which the gross rate of O2 evolution was known from previous
studies (Strand 1995, Strand and Lundmark 1995). In addition,

new samples of current-year needles were collected from C, I
and IL trees to document the interrelationships between oxygen exchange (photosynthetic O2 evolution at high irradiances
and O2 uptake in darkness), chlorophyll a fluorescence and
content of mineral nutrients.

Materials and methods
Experimental site and plant material
The plant material for this investigation was obtained from the
Flakaliden research area (64°07′ N, 19°27′ E, altitude 310-320 m above sea level). The area, which is located about 50 km
northwest of Umeå in northern Sweden, was planted with
Norway spruce (Picea abies) seedlings of local provenance in
1963 after clear-felling. Different plots at the experimental site
were given the following treatments: irrigation (I), annual
application of a complete mix of solid fertilizers (F) and
irrigation plus liquid fertilization (IL), in addition to the control (C). In the IL treatment, a complete nutrient solution was
injected into the irrigation water and applied every day during
the growing season. The treatments commenced in 1987 when
the mean height of the trees was about 2.6 m. More detailed
descriptions of the experimental site and treatments are given
in Flower-Ellis (1993) and Linder (1995). In the study described here, trees from the C-, I- and IL-treated plots were

investigated.
From April 6 to August 11, 1992, second-order one-year-old
shoots were collected from south-facing branches of the seventh whorl from the top of each of five trees from a C and an
IL plot. Second-order current-year sun shoots were collected
from south-facing branches of the third whorl of the same trees
on September 23 and December 8, 1992. Current-year shade
shoots were collected from the lowest branches of five other
trees from the same plots on October 7 and December 14,
1992. In 1993, second-order current-year sun shoots were
collected from south-facing branches of the third whorl of five
trees from each of four C, two I and four IL plots over a 2-week
period (September 12 to September 28). Samples were stored
in darkness at 0 °C, and measurements were made after at least

2 h, but within three days. No consistent change in the measured characteristics occurred during the storage period.
Measurements of oxygen exchange and chlorophyll
fluorescence
Oxygen exchange of needles was measured at 20 °C and 5 kPa
CO2 with a leaf-disc oxygen electrode (LD2 with control box
CB1; Hansatech Ltd., King’s Lynn, U.K.). Use of this equipment has been described by Strand (1995) and Strand and

Lundmark (1995) for samples collected in 1992. For samples
collected in September 1993, chlorophyll a fluorescence was
measured simultaneously with O2 exchange using an adapted
top window for the fiber optic cable of the modulation
fluorometer (PAM Chlorophyll Fluorometer; H. Walz, Effeltrich, Germany), described by Schreiber et al. (1986). The
fluorescence nomenclature of van Kooten and Snel (1990) has
been adopted.
Each sample had a projected area of 2.1 ± 0.2 cm2 (mean ±
SD), and consisted of needles detached from shoots stored in
darkness at 0 °C for at least 2 h. Samples were enclosed in the
leaf-disc chamber in darkness and excited with a weak measuring beam from a pulsed light-emitting diode to obtain the
minimum (dark) fluorescence yield (F0). To determine the
maximum fluorescence yield (FM), each sample was then
exposed to a 1-s saturating pulse of white light from a modified
Schott fiber illuminator KL 1500 (FL 103; H. Walz). Following determination of F0 and FM, needles were illuminated with
actinic white light from a Schott fiber illuminator (FL 101;
H. Walz) for approximately 30 min. The irradiance was 600 ±
10 µmol m −2 s −1. Maximum fluorescence (FM ′) and minimum
fluorescence (F0′) in the light-adapted state were determined
by applying 1-s saturating pulses at 200-s intervals, and by

switching off actinic light, respectively. Variable fluorescence
yields, FV and FV ′, were calculated as FM − F0 and FM ′ − F0′,
respectively.
Rates of photosynthesis were expressed as the gross rate of
O2 evolution; i.e., the sum of O2 evolution in light and O2
uptake in darkness. Dark respiration in light was estimated
after 10 min in darkness. Steady-state photochemical quenching (qP) was calculated as (FM ′ − F) /(FM ′ − F0′), where F is the
fluorescence yield in the light-adapted state (van Kooten
and Snel 1990). Stern-Volmer non-photochemical quenching (SVN) was calculated as FM /FM ′ − 1 (Krause and Weis
1991), whereas Stern-Volmer F0-quenching was calculated as
F0 /F0′ − 1. The quantum efficiency of photosystem II (ΦPSII )
was calculated as (FM ′ − F) /FM ′ (Genty et al. 1989).
Irradiance was measured with a quantum sensor (LI-190SB,
Li-Cor, Inc., Lincoln, NE). The projected area of needles was
determined with a leaf area meter (Delta-T Devices, Cambridge, U.K.), and needle dry mass was determined after drying for 24 h at 80 °C.
Chemical analyses
The contents of C and total N in needles were determined with
a CHN elemental analyzer (Perkin-Elmer, Model 2400 CHN).
The contents of P, K, Ca, Mg and S in needles were analyzed
with an inductively coupled plasma (ICP) analyzer (Perkin-El-

PHOTOSYNTHESIS IN NORWAY SPRUCE NEEDLES

223

mer, Model Plasma 2) after wet digestion with HClO4/HNO3.
Analyses were carried out according to the protocol routinely
used at the Department of Forest Ecology, the Swedish University of Agricultural Sciences, Umeå.
Statistical analyses
Data were analyzed using the StatView statistical package
(StatView 4.5, Abacus Concepts Inc., Berkeley, CA). One-way
analysis of variance and Fisher’s protected LSD test were used
to establish significant differences at P ≤ 0.05 between treatment means. However, nonparametric tests (Mann-Whitney’s
U-test or Kruskal-Wallis’ test) were used when application of
Bartlett’s test for homogeneity of variances indicated significant differences in variance between treatments. Interrelations
between oxygen exchange, chlorophyll fluorescence, and mineral nutrient content were evaluated with least squares linear
and polynomial regression analyses.

Results and discussion
Mass per unit area and mineral nutrient content

Dry mass per unit area in one-year-old needles from the seventh whorl was higher after the main recovery of photosynthesis in May (Days 132--146) than earlier in the spring
(Figures 1A and 1B), but there was no significant difference in
mass/area between C and IL trees on any sampling occasion.
The variation in mass/area can be explained by seasonal variation in the starch content of one-year-old needles (see Linder
1995). The N content was generally significantly higher in
one-year-old needles of IL trees than in those of C trees
(Figure 1C). Furthermore, the N content tended to be lower
after the main recovery of photosynthesis than earlier in spring.
This is consistent with observations of a small decrease in N
content during early summer, even when expressed on a structural dry mass basis; i.e., after correction for nonstructural
carbohydrates (Flower-Ellis 1993, Linder 1995). The decline
in N content during early summer can be attributed to the
retranslocation of N to developing needles and shoots (Nambiar and Fife 1991).
Current-year sun and shade needles were collected from the
third whorl and from the bottom of the canopy, respectively, of
C and IL trees in both autumn and early winter 1992 (Table 1),
whereas in 1993, current-year sun needles from the third whorl
of C, I, and IL trees were collected in September only (Table 2).
As previously noted for one-year-old needles, mass/area in
current-year sun needles was not significantly affected by the

treatments (Tables 1 and 2). Sun needles of IL trees had
substantially higher contents of N, P, K and S, but a lower
content of Ca than sun needles of C trees when expressed on a
projected needle area basis (Tables 1 and 2). The content of N
and other macronutrients in sun needles of C and I trees did not
differ significantly (Table 2). Because mass/area in sun needles
was not significantly affected by the treatments (Tables 1 and
2), similar results were obtained when the amount of mineral
nutrients in the needles was expressed on a dry mass basis (data
not shown).

Figure 1. Dry mass per unit area (A), gross rate of oxygen evolution at
an irradiance of 750 ± 50 µmol m −2 s −1 (B; modified from Strand and
Lundmark 1995) and nitrogen content (C) in one-year-old needles
from the seventh whorl of control (s) and irrigated-fertilized (e)
Picea abies during spring and summer. The SE bars are included when
larger than the symbols. Asterisks represent significant differences
between treatments at P < 0.05 (*) and P < 0.01 (**).

Shade needles had a lower mass/area ratio than sun needles
(Table 1). Furthermore, shade needles of IL trees had a lower
mean mass/area than shade needles of C trees, probably as a
result of the lower irradiances at the bottom of the canopy in
IL-treated plots (data not shown). The lower content of N and
other macronutrients in shade needles than in sun needles of C
and IL trees was primarily due to differences in mass/area
(Table 1). Hence, the amount of N on a dry mass basis was not
significantly different between sun and shade needles of either
C trees or IL trees (data not shown).
Relationships between gross oxygen evolution and mineral
nutrient content
The higher N content of one-year-old needles of IL trees was
associated with a higher rate of gross O2 evolution at high
irradiances in needles of IL trees than in corresponding needles

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STRAND

Table 1. Dry mass and content of macronutrients expressed on a projected area basis (g m −2) in current-year needles of control (C) and
irrigated-fertilized (IL) Picea abies. Means ± SE are shown for n = 4--5. Other values represent pooled samples from 4--5 trees. Within a row,
significant differences (P ≤ 0.05) are marked by different letters.
Variable

Treatment
Sun needles

F-value

P-value

Shade needles

C

IL

C

IL

September--October 1992
Mass/area
N
P
K
Ca
Mg
S

350 ± 16 a
3.02 ± 0.13 a
0.39
1.49
1.39
0.38
0.23

343 ± 19 a
4.42 ± 0.26 b
0.79
2.40
1.08
0.32
0.33

195 ± 17 b
1.76 ± 0.16 c
0.27
1.07
0.66
0.20
0.13

155 ± 9 b
1.83 ± 0.27 c
0.28
1.07
0.75
0.16
0.13

41.231
31.654

< 0.0001
< 0.0001

December 19922
Mass/area
N
P
K
Ca
Mg
S

343 ± 9 a
3.03 ± 0.10 a
0.38 ± 0.02 a
1.50 ± 0.10 a
1.58 ± 0.17 a
0.41 ± 0.02 a
0.24 ± 0.01 a

349 ± 9 a
4.48 ± 0.29 b
0.76 ± 0.07 b
2.43 ± 0.21 b
1.01 ± 0.17 b
0.31 ± 0.04 a
0.32 ± 0.01 b

225 ± 15 b
2.03 ± 0.12 c
0.31
1.08
0.81
0.25
0.15

144 ± 8 c
1.82 ± 0.14 c
0.29
1.18
0.56
0.14
0.12

86.416
45.599

< 0.0001
< 0.0001
0.0090
0.0042
0.0431
0.0707
0.0007

1

1
2

15.605
5.764
4.342
28.428

Sun and shade needles were collected on September 23 and October 7, respectively.
Sun and shade needles were collected on December 8 and December 14, respectively.

Table 2. Dry mass and content of macronutrients expressed on a projected area basis (g m −2) in current-year needles from the third whorl of control
(C), irrigated (I) and irrigated-fertilized (IL) Picea abies. Samples were collected from September 12 to September 28, 1993. Means ± SE are
shown. Within a row, significant differences (P ≤ 0.05) are marked by different letters.
Variable

Mass/area
N
P
K
Ca
Mg
S

Treatment
C (n = 20)

I (n = 10)

IL (n = 20)

361 ± 8 a
3.79 ± 0.11 a
0.55 ± 0.02 a
2.05 ± 0.12 a
1.29 ± 0.07 a
0.34 ± 0.01 a
0.25 ± 0.01 a

381 ± 11 a
3.38 ± 0.20 a
0.49 ± 0.03 a
1.79 ± 0.10 a
1.32 ± 0.06 a
0.33 ± 0.02 a
0.23 ± 0.01 a

370 ± 8 a
5.15 ± 0.17 b
0.89 ± 0.04 b
3.02 ± 0.11 b
1.10 ± 0.06 b
0.34 ± 0.01 a
0.33 ± 0.01 b

of C trees both before and after the main recovery of photosynthesis in spring (Figures 1B and 1C). The slope of the relationship between O2 evolution rate and foliar N content across
treatments was significant on all three sampling occasions
before the recovery of photosynthesis, but on only three of the
six sampling occasions following recovery (data not shown).
The generally weak photosynthesis--N relationships in oneyear-old needles (mean r 2 = 0.44 for all sampling occasions)
were probably a result of both the small number of samples on
each sampling occasion and the relatively small variation in
needle N content. However, mean values of O2 evolution rate
in needles of C and IL trees on the sampling occasions after the

F-value

P-value

1.242
33.321
47.374
30.029
3.423
0.206
31.811

0.2980
< 0.0001
< 0.0001
< 0.0001
0.0410
0.8146
< 0.0001

main recovery of photosynthesis were correlated with mean
values of needle N content (r 2 = 0.630; P = 0.0021).
For current-year needles collected in autumn 1992, O2 evolution rate was correlated with needle N content when the latter
varied in response to irrigation-fertilization and gradients of
light availability (Figure 2A). The existence of linear relationships between the light-saturated rate of CO2 assimilation or
O2 evolution and leaf N content along gradients of light availability in canopies has been demonstrated in several studies
(e.g., Hirose and Werger 1987, DeJong et al. 1989, Ellsworth
and Reich 1993, Evans 1993). DeJong et al. (1989) found that
the photosynthesis--N relationship across canopy light gradi-

PHOTOSYNTHESIS IN NORWAY SPRUCE NEEDLES

ents was different in N-fertilized and unfertilized trees of
Prunus persica (L.) Batsch., but no such difference between
treatments was observed in current-year needles of Norway
spruce in this study.
The relationship between O2 evolution rate and foliar N
content across treatments and canopy light gradients appeared
to be maintained from autumn to early winter (Figure 2A).
Some variation in this relationship might be expected during
the winter because winter inhibition of the near light-saturated
rate of O2 evolution has been found to differ in sun and shade
needles, irrespective of treatment (Strand 1995). Furthermore,
the inhibition of the rate of O2 evolution at high irradiances
appeared to be more pronounced in shade needles of IL trees
than in shade needles of C trees (Strand 1995). However, the
potential rate of photosynthesis in the upper part of the canopy
may be dependent on needle N content throughout the winter,

225

as indicated by the significantly higher rate of O2 evolution in
one-year-old needles of IL trees than in one-year-old needles
of C trees during late winter and spring (Figure 1B).
The relationship between O2 evolution rate and mineral
nutrient content in current-year needles from the third whorl
was further investigated in September 1993. As previously
found for current-year needles in 1992 (Strand 1995), the gross
rate of O2 evolution at an irradiance of 600 µmol m −2 s −1,
whether expressed on a projected needle area basis or on a dry
mass basis, was significantly higher in needles of IL trees than
in needles of C trees (Table 3). Furthermore, needles of I trees
had a significantly lower rate of O2 evolution than needles of
C trees (Table 3). A relatively strong relationship between the
gross rate of O2 evolution and foliar N content was obtained
across treatments (Figure 3A). This is in agreement with the
strong positive correlation often observed between CO2-satu-

Figure 2. Gross rate of oxygen evolution at an irradiance of 1020 ± 10 µmol m −2 s −1 as a function of the content of nitrogen (A), phosphorus (B),
potassium (C) and sulfur (D) in current-year sun (control: s, d; irrigated-fertilized: e, r) and shade (control: ,, .; irrigated-fertilized: h, j)
needles of Picea abies in September--October (open symbols, solid line) and December (filled symbols, broken line), 1992. Means ± SE for n = 4--5
(gross rate of oxygen evolution) and values representing pooled samples from 4--5 trees (mineral nutrient content) are shown in B--D. Regression
equations are given in the figures.

Table 3. Rates of gross oxygen evolution and dark respiration (expressed on a projected needle area basis and on a dry mass basis), and
characteristics of chlorophyll fluorescence, including the ratio of variable to maximum fluorescence in darkness (FV/FM ) and in light (FV′/FM ′),
Stern-Volmer nonphotochemical quenching (SVN), Stern-Volmer quenching of minimum fluorescence (SV0), photochemical quenching (qP), and
quantum efficiency of PS II (ΦPSII ) in current-year needles from the third whorl of control (C), irrigated (I) and irrigated-fertilized (IL) Picea abies.
Steady-state measurements of the rate of gross O2 evolution and fluorescence characteristics were made at an irradiance of 600 ± 10 µmol m −2 s −1.
The rate of dark respiration was measured as O2 uptake after 10 min in darkness. Samples were collected from September 12 to September 28,
1993. Means ± SE are shown. Within a row, significant differences between treatments (P ≤ 0.05) are marked by different letters.
Variable
Gross O2 evolution (µmol m −2 s −1)
Gross O2 evolution (nmol g −1 s −1)
Dark respiration (µmol m −2 s −1)
Dark respiration (nmol g −1 s −1)
F V/F M
F V′/F M ′

SVN
SV0
qP
ΦPSII = qP × FV ′/FM′

Treatment
C (n = 20)

I (n = 10)

IL (n = 20)

13.6 ± 0.6 a
37.7 ± 1.7 a
2.5 ± 0.1 a
7.0 ± 0.3 a
0.71 ± 0.01 a
0.49 ± 0.02 a
1.07 ± 0.05 a
0.17 ± 0.02 a
0.78 ± 0.01
0.39 ± 0.02 a

11.2 ± 0.8 b
29.6 ± 2.0 b
2.3 ± 0.1 a
6.2 ± 0.4 a
0.70 ± 0.01 a
0.43 ± 0.02 b
1.33 ± 0.08 b
0.22 ± 0.02 a
0.73 ± 0.02
0.32 ± 0.02 b

17.7 ± 0.6 c
48.8 ± 1.8 c
3.0 ± 0.1 b
8.1 ± 0.3 b
0.78 ± 0.01 b
0.59 ± 0.01 c
0.97 ± 0.04 a
0.05 ± 0.01 b
0.82 ± 0.01
0.49 ± 0.01 c

F-value

P-value

21.788
23.364
6.445
8.363
17.422
23.830
8.955
21.546

< 0.0001
< 0.0001
0.0034
0.0008
< 0.0001
< 0.0001
0.0005
< 0.0001
< 0.0001
< 0.0001

23.769

226

STRAND

rated rate of CO2 assimilation and foliar N content in response
to varying N nutrition (e.g., Seemann et al. 1987, Sage et al.
1990, Tan and Hogan 1995). The relationship plotted in Figure 3A was based on samples collected from different trees on
four occasions over a two-week period. On one of these sampling occasions, needles from all three treatments had low rates
of gross photosynthesis in relation to their N content (data not
shown), and r 2 increased from 0.662 to 0.737 if these data were
excluded. No plausible explanation, such as exceptional
weather conditions, could be found for the low rate of gross O2
evolution on this occasion.
The rate of gross O2 evolution was strongly correlated with
the contents of P, K and S in the needles both in autumn and
early winter of 1992 (Figures 2B--D), partly because these
relationships were based on mean values (O2 evolution rate) or
values representing pooled samples (content of mineral nutrients). In September 1993, linear regressions of O2 evolution
rate with needle P, K and S contents indicated that the rate of
O2 evolution was almost equally well correlated with the
contents of P (Figure 3B) and S (Figure 3D) as with the content
of N, but the relationship between O2 evolution rate and K
content was weaker (Figure 3C). These relationships may have
arisen because needle P, K and S contents were correlated with
N content (r 2 = 0.49--0.81). Consequently, it was not surprising
that only the regression coefficient for N content was significant in a multiple regression analysis with O2 evolution rate as
the dependent variable and needle N, P, K and S contents as
independent variables. Furthermore, growth (and presumably
also photosynthetic electron transport) was not limited by P, K,
or S because ratios of these elements to N (data not shown)
were above those considered critical (see Linder 1995). No
relationship between the rate of O2 evolution and the foliar
content of Ca (r 2 = 0.007; P = 0.57) or Mg (r 2 = 0.029;
P = 0.24) was observed for current-year needles in September
1993.
Mass-based photosynthesis--N relationships were weaker
than area-based relationships for needles collected in the
autumn and winter of 1992 (data not shown). However, r 2 of
the mass-based photosynthesis--N relationship in September

1993 was 0.68, a value similar to that of the area-based expression (Figure 3A). Because only sun needles from the third
whorl were examined in September 1993, the relative strength
of mass-based and area-based relationships may depend on
whether the relationship is examined across canopy light gradients. This is consistent with previous reports of a lack of
mass-based correlations between the light-saturated rate of
CO2 assimilation and N content across canopy light gradients
(e.g., DeJong et al. 1989, Ellsworth and Reich 1993). In addition to the similar r 2 value, the slope of the mass-based photosynthesis--N relationship (3.35 µmol O2 (g N) −1 s −1) was
similar to that of the area-based relationship in September
1993 (Figure 3A).
Dependence of dark respiration on gross oxygen evolution
and nitrogen content
The correlation between the rate of dark respiration measured
as O2 uptake and the preceding rate of gross O2 evolution in
current-year needles was relatively strong both in autumn and
early winter 1992 (Figure 4A). This relationship appeared to
be maintained when the rate of O2 evolution during preillumination was varied by changing the irradiance (data not shown;
cf. Strand 1995). For samples collected in September 1993, the
rate of O2 uptake, whether expressed on a projected needle area
basis or on a dry mass basis, was significantly higher in
current-year needles of IL trees than in current-year needles of
C and I trees (Table 3). Furthermore, a linear relationship
between the rate of dark respiration and the preceding rate of
gross O2 evolution across treatments was obtained, regardless
of whether rates were expressed on a needle area basis (Figure 5A) or on a dry mass basis (r 2 = 0.509; P < 0.0001).
Similarly, Stokes et al. (1990) observed an enhancement of O2
uptake after minutes of preillumination, which persisted for
about 10 min in darkness. This light-enhanced dark respiration
was dependent on the amount of preceding photosynthesis and
was attributed to reoxidation of early photosynthetic products
in the chloroplast stroma. After short periods of preillumination, the enhancement of O2 uptake is probably not accompanied by a corresponding enhancement of CO2 efflux (Stokes

Figure 3. Gross rate of oxygen evolution at an irradiance of 600 ± 10 µmol m −2 s −1 as a function of the content of nitrogen (A), phosphorus (B),
potassium (C) and sulfur (D) in current-year needles from the third whorl of control (s), irrigated (n) and irrigated-fertilized (e) Picea abies.
Samples were collected from September 12 to September 28, 1993. Regression equations are given in the figures.

PHOTOSYNTHESIS IN NORWAY SPRUCE NEEDLES

227

Figure 4. Rate of dark respiration measured after 5 min in darkness as
a function of the preceding rate of gross oxygen evolution at an
irradiance of 1020 ± 10 µmol m −2 s −1 (A), and nitrogen content (B) in
current-year sun (control: s, d; irrigated-fertilized: e, r) and shade
(control: ,, .; irrigated-fertilized: h, j) needles of Picea abies in
September--October (open symbols, solid line) and December (filled
symbols, broken line), 1992. Regression equations are given in the
figures.

Figure 5. Rate of dark respiration measured after 10 min in darkness
as a function of the preceding rate of gross oxygen evolution at an
irradiance of 600 ± 10 µmol m −2 s −1 (A) and nitrogen content (B) in
current-year needles from the third whorl of control (s), irrigated (n)
and irrigated-fertilized (e) Picea abies. Samples were collected from
September 12 to September 28, 1993. Regression equations are given
in the figures.

et al. 1990). However, after longer periods of preillumination
(hours), the rate of CO2 efflux in darkness can be correlated
positively with the amount of preceding photosynthesis in
mature leaves (e.g., Azcón-Bieto and Osmond 1983). This
effect of photosynthesis on subsequent respiration is thought
to be mediated by an accumulation of nonstructural carbohydrates in the leaves (Azcón-Bieto and Osmond 1983, AzcónBieto 1992).
In addition to the content of nonstructural carbohydrates,
leaf N content may be correlated with CO2 efflux in darkness
(Hirose and Werger 1987, Sheriff and Nambiar 1991, Wull-

schleger et al. 1992, Ryan 1995). For example, Ryan (1995)
found that CO2 efflux at night was correlated with needle N
content in fully expanded foliage of several species of conifers
when data were expressed on a dry mass basis. However, dark
respiration and leaf N content have also been reported to be
unrelated (e.g., Byrd et al. 1992). For current-year needles
collected in autumn and early winter 1992, the rate of O2
uptake was equally well correlated with N content as with the
preceding rate of O2 evolution (Figure 4B cf. Figure 4A),
whereas the rate of dark respiration for current-year needles in
September 1993 was less dependent on N content than on the

228

STRAND

previous rate of photosynthesis (Figure 5B cf. Figure 5A).
Although the relationships between dark respiration rate and
N content may indirectly result from correlations between O2
evolution rate and N content (Figures 2A and 3A), the portion
of dark respiration associated with protein repair and replacement is often thought to increase with increasing N content
(Ryan 1991, 1995). It is possible that the rate of dark respiration measured after periods of darkness longer than those used
in the present study would be more closely linked to needle N
or protein content than to the preceding rate of photosynthesis.
Relationship between chlorophyll fluorescence and gross
oxygen evolution
The FV /FM ratio was significantly higher in current-year needles of IL trees than in current-year needles of C and I trees,
whereas FV′/FM ′ was significantly different between all three
treatments in September 1993 (Table 3). These results are in
agreement with those obtained in autumn 1992 (Strand 1995),
although only four or five trees from each of the C and IL
treatments were examined that year. Both FV/FM and FV′/FM ′
were strongly correlated with the rate of gross O2 evolution at
an irradiance of 600 µmol m −2 s −1 (Figure 6A) and, presumably, also with the rate of photosynthetic electron transport. In
the model of Genty et al. (1989), FV′/FM ′ represents the quantum efficiency of open PS II reaction centers, which is assumed
to depend on thermal energy dissipation in the antennae. Nonradiative energy dissipation is considered to be a ubiquitous
mechanism for protection of the photosynthetic reaction centers against excessive excitation (Demmig-Adams and Adams
III 1992, Björkman and Demmig-Adams 1994, Long et al.
1994). Nitrogen limitation, which restricts the utilization of
excitation energy in photosynthetic electron transport at high
irradiances (see Evans 1989), presumably increases the
amount of excessive light energy in PS II. Consequently, the
observed response of FV′/FM ′ to changes in O2 evolution rate
seems appropriate.
Nonradiative energy dissipation according to the Stern-Volmer equation (SVN) was significantly lower in needles of C and
IL trees than in needles of I trees, whereas Stern-Volmer
quenching of minimum fluorescence (SV0) was significantly
lower in needles of IL trees than in needles of C and I trees
(Table 3). Values of SVN were only weakly correlated with
FV/FM and FV′/FM ′ (data not shown), and with the gross rate of
O2 evolution (Figure 6B). In contrast, the relationship between
SV0 and O2 evolution rate was strong (Figure 6C). Furthermore, SV0 was strongly correlated with FV/FM and FV′/FM ′,
but only weakly correlated with SVN (data not shown). The
proportion of open PS II reaction centers, as indicated by qP,
decreased slightly with a decreasing rate of photosynthesis
(Figure 6B). Because treatment-related differences in qP existed (Table 3), needles from the different treatments may be
differentially susceptible to excess light (cf. Ögren 1991),
despite counteracting changes in thermal energy dissipation.
The quantum efficiency of PS II (ΦPSII ) differed significantly
between the treatments (Table 3), primarily because of variations in FV′/FM ′. The relationship between ΦPSII and the
apparent quantum yield of O2 evolution (the rate of gross O2

Figure 6. Characteristics of chlorophyll fluorescence as a function of
the rate of gross oxygen evolution at an irradiance of 600 ± 10 µmol
m −2 s −1 in current-year needles from the third whorl of control (s, d),
irrigated (n, m) and irrigated-fertilized (e, r) Picea abies. (A) Ratio
of variable to maximum fluorescence in darkness (FV/FM , open symbols) and in light (FV′/FM ′, filled symbols). (B) Photochemical
quenching (qP, open symbols) and Stern-Volmer nonphotochemical
quenching (SVN, filled symbols). (C) Stern-Volmer quenching of
minimum fluorescence (SV0). Regression equations are given in the
figures.

PHOTOSYNTHESIS IN NORWAY SPRUCE NEEDLES

evolution/irradiance) in current-year needles during autumn
and early winter 1992 (Strand 1995) was similar to that in
one-year-old needles during spring and early summer 1992
(Strand and Lundmark 1995). A wide range of irradiances was
used during the measurements in 1992, whereas in September
1993, the irradiance was fixed at approximately 600 µmol
m −2 s −1. At this predetermined irradiance, ΦP S I I became linearly related to the rate of gross O2 evolution (r 2 = 0.883;
P < 0.0001; data not shown). As noted above, other fluorescence characteristics (FV/FM , FV′/FM ′and SV0) were also
closely correlated with the rate of CO2-saturated photosynthesis (Figures 6A and 6C). This suggests that the level of excitation energy in PS II of Norway spruce needles is tightly
regulated at high irradiances when photosynthetic electron
transport is limited by the availability of N.

Conclusions
I conclude that a major part of the variation in CO2-saturated
photosynthesis at high irradiances and at a particular time of
the year is associated with differences in foliar N content,
especially when photosynthetic rate and foliar N content are
expressed on a projected needle area basis. However, further
work is needed to document whether this is also true at typical
CO2 concentrations in the field. Similar to the gross rate of O2
evolution, the rate of dark respiration, measured as O2 uptake
after 5 or 10 min of darkness, was positively correlated with
needle N content in current-year needles. A positive linear
relationship between the rate of dark respiration and the preceding rate of photosynthesis was also obtained. Furthermore,
certain chlorophyll fluorescence characteristics (variable to
maximum fluorescence in the dark- and light-adapted states,
as well as Stern-Volmer quenching of minimum fluorescence)
indicative of nonradiative energy dissipation in PS II were
strongly correlated with the gross rate of O2 evolution at a high
fixed irradiance in current-year sun needles, implying that
adjustments in the thermal energy dissipation within PS II had
occurred in response to changes in photosynthetic electron
transport.

Acknowledgments
I am grateful to Professor Sune Linder and Dr. Anders Ericsson for
their comments on the manuscript. This investigation was supported
by the Swedish Council for Forestry and Agricultural Research.

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