Tree Physiology 20, 1249–1254
© 2000 Heron Publishing—Victoria, Canada
Photosynthetic nitrogen-use efficiency in evergreen broad-leaved
woody species coexisting in a warm-temperate forest
KOUKI HIKOSAKA and TADAKI HIROSE
Biological Institute, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan
Received February 10, 2000
Summary Photosynthetic nitrogen-use efficiency (PNUE,
photosynthetic capacity per unit leaf nitrogen) varies among
species from different habitats and correlates with several ecological characteristics such as leaf life span and leaf mass per
area. We investigated eight evergreen broad-leaved woody
species with different leaf life spans that coexist in a
warm-temperate forest. We determined photosynthetic capacity at ambient CO2 concentration in saturated light, nitrogen
concentration, and the concentration of ribulose-1,5-bisphosphate carboxylase (RuBPCase), a key enzyme of photosynthesis and the largest sink of nitrogen in leaves. Each species
showed a strong correlation between photosynthetic capacity
and RuBPCase concentration, and between RuBPCase concentration and nitrogen concentration. Photosynthetic capacity
of leaves decreased with increasing leaf life span, whereas
PNUE did not correlate significantly with leaf life span. There
was a twofold variation in PNUE among species. This relatively small variation in PNUE is consistent with the argument
that species that coexist in a single habitat maintain a similar
PNUE. The two components of PNUE—photosynthetic rate
per unit RuBPCase and RuBPCase per unit leaf nitrogen—were not significantly correlated with other leaf characteristics such as leaf life span and leaf mass per area. We conclude that differences in PNUE are relatively small among coexisting species and that differences in absolute amounts of
photosynthetic proteins lead to differences in photosynthetic
productivity among species.
Keywords: coexistence, leaf life span, leaf nitrogen, leaf photosynthesis, ribulose-1,5-bisphosphate carboxylase.
Introduction
Within a species, photosynthetic capacity (Pmax) is strongly
correlated with leaf nitrogen concentration. This correlation
has been attributed to the large fraction of leaf nitrogen allocated to the photosynthetic apparatus (Evans 1989). However,
it is also known that, when compared at the same nitrogen concentration, photosynthetic capacity exhibits large variation
among species (Field and Mooney 1986). Although nitrogen
is one of the most important elements limiting plant growth, it
is not known why some species have a consistently low photosynthetic nitrogen-use efficiency (PNUE, Pmax per unit leaf ni-
trogen).
Many studies have focused on PNUE in relation to ecological characteristics of species (Chazdon and Field 1987,
Poorter et al. 1990, Reich et al. 1991, 1994, 1995, 1997, Reich
and Walters 1994, Ellsworth and Reich 1996, Loomis 1997).
These studies have shown that low PNUEs tend to occur in
species that are stress-tolerant (Chazdon and Field 1987,
Poorter et al. 1990, Reich et al. 1994) and in late-successional
species (Reich and Walters 1994, Reich et al. 1994, Ellsworth
and Reich 1996). Reich et al. (1991) compared leaf characteristics of 23 tropical rain forest species and found that PNUE is
low in species that have a relatively long leaf life span, high
leaf mass per area and tough leaves.
Field and Mooney (1986) proposed four physiological factors that may cause variation in PNUE among species: (1) CO2
concentration at the carboxylation site, (2) allocation of nitrogen to the photosynthetic apparatus, (3) partitioning of nitrogen among photosynthetic components, and (4) specific
activity of photosynthetic enzymes. Several studies have
shown that, compared with species with high PNUE, species
with low PNUE tend to have a lower CO2 concentration at the
carboxylation site (Lloyd et al. 1992, Epron et al. 1995,
Hikosaka et al. 1998) and a smaller allocation of leaf nitrogen
to the photosynthetic apparatus (Lloyd et al. 1992, Hikosaka et
al. 1998, Poorter and Evans 1998). Although several physiological factors have been shown to be associated with variation in PNUE, their relationships with leaf ecological
characteristics, such as leaf life span, have not been examined.
We investigated eight evergreen woody species with various leaf life spans that coexist in a warm-temperate forest.
Characteristics such as leaf life span, leaf mass per area, leaf
nitrogen and in situ photosynthetic capacity were determined
in leaves exposed to similar light conditions. We also measured the concentration of ribulose-1,5-bisphosphate
carboxylase (RuBPCase), a key enzyme of photosynthesis and
the largest sink of nitrogen in a leaf (Evans 1989). Relationships between Pmax, RuBPCase concentration and nitrogen
concentration were compared among species. Photosynthetic
nitrogen-use efficiency may be expressed as the product of
Pmax per unit RuBPCase and RuBPCase per unit nitrogen. A
decrease in CO2 concentration at the carboxylation site may
lead to a decrease in Pmax per unit RuBPCase because CO2 is
the substrate of the carboxylation reaction. Differences in allo-
1250
HIKOSAKA AND HIROSE
cation of nitrogen to the photosynthetic apparatus are reflected
in differences in RuBPCase per unit nitrogen. Therefore, we
also investigated relationships between these photosynthetic
parameters and leaf ecological characteristics such as leaf life
span, leaf mass per area and leaf nitrogen concentration.
Materials and methods
The study site is located in a warm-temperate forest of the Tokyo University Forest on Mt. Kiyosumi, Chiba, Japan
(35°12′ N, 140°9′ E, 300 m a.s.l.). The dominant tree species
are Quercus acuta Thunb. and Castanopsis sieboldii (Makino)
Hatusima ex Yamazaki et Mashiba. A detailed description of
the vegetation of this forest has been presented elsewhere
(Sakai and Ohsawa 1993). The study site is a natural forest developed on a ridge that had been protected for more than
60 years. In 1991, an adjacent plantation of Japanese cedar
was clearcut, creating a forest edge facing east that extended
from the north to the south of the study site. Woody species occurring at the forest edge and within the forest were used in
this study (Table 1).
Leaf life span was determined by a full 2-year census from
1996 to 1998. Branches were marked and fates of leaves were
followed every 6 months. Leaf longevity (L) was calculated
as:
L = n0 ∆ T / n L ,
(1)
where nL is the number of leaves lost during the census, ∆T is
the duration of the census, and no is the initial number of leaves
(Ackerly and Bazzaz 1995).
Photosynthetic rates of leaves were measured with a portable photosynthetic measurement system (LCA-3, Analytical
Development Company, Hoddesdon, U.K.) with an artificial
illumination system (halogen lamp). Leaves were measured at
ambient CO2 concentrations, air temperature, relative humidity and saturating irradiance. Mean leaf temperature was
34.7 ± 1.1 °C. Measurements were made on July 18 and 19,
1996. Photosynthetic capacities were determined for both
plants grown at the forest edge and those grown within the forest. At the forest edge, young and fully expanded leaves exposed to the sun were selected. After measurement, leaves
were harvested and chlorophyll (chl) concentration was deter-
Table 1. Height of adult trees of the woody species measured in the
study.
Species (family)
Height (m)
Castanopsis sieboldii (Fagaceae)
Quercus acuta (Fagaceae)
Camellia japonica L. (Theaceae)
Cleyera japonica Thunb. (Theaceae)
Cinnamomum japonicum Sieb. ex Nakai (Lauraceae)
Neolitsea sericea (Bl.) Koidz. (Lauraceae)
Illicium anisatum L. (Illiciaceae)
Maesa japonica (Thunb.) Moritzi (Myrsinaceae)
16
16
11
7
10
3
7
0.5
mined with a chlorophyll meter (SPAD, Minolta, Osaka, Japan), which was calibrated according to the method described
by Porra et al. (1989). Three leaf discs of 1-cm diameter were
punched out from each leaf and dried in an oven (70 °C). Dry
mass and nitrogen concentration of the dried leaf discs were
determined as described by Hikosaka et al. (1994). The remainder of each leaf was frozen in liquid nitrogen and stored
at –80 °C for later determination of RuBPCase concentration.
The RuBPCase concentration was determined according to
Hikosaka et al. (1998). The frozen leaf was homogenized in
100 mM sodium phosphate buffer (pH 7.5) containing 0.4 M
sorbitol, 10 mM NaCl, 2 mM MgCl2, 5 mM iodine acetate,
1 mM phenylmethyl sulfonyl fluoride, 5 mM dithiothreitol
and 2% (w/v) polyvinylpyrrolidon. After filtration through
20-µm mesh, the filtrate was applied to SDS-PAGE. The gel
was stained with Coomassie Brilliant Blue R-250 (CBB). The
band of the large subunit of RuBPCase was extracted with
formamide for spectrophotometric determination of RuBPCase. Calibration curves were made with RuBPCase purified
from Spinacia oleracea L. The RuBPCase concentration per
unit leaf area was calculated as the product of the RuBPCase/chl ratio and chl concentration per unit leaf area.
Results
Figure 1 shows Pmax (photosynthetic rate per unit area at ambient CO2 concentration in saturated light) (a), leaf nitrogen concentration per unit area (b), leaf nitrogen concentration per
unit mass (c), leaf mass per unit area of sun leaves of eight species (d), and PNUE (Pmax per unit leaf nitrogen) (e) as a function of leaf life span. Although all species were evergreen,
some species had leaf life spans of less than 1 year. We note
that these species had leaf life spans longer than 1 year when
grown in shaded conditions (data not shown). Photosynthetic
capacity exhibited a significantly negative correlation with
leaf life span. Other characteristics measured were not correlated with leaf life span. Nitrogen concentration per unit leaf
area tended to decrease with leaf life span, although the correlation was not significant (P = 0.12).
Figure 2 shows the relationship between Pmax and nitrogen
concentration per unit leaf area in each species. These data include both sun and shade leaves to obtain large variation in the
leaf nitrogen concentration. Six species (Quercus acuta, Camellia japonica, Castanopsis sieboldii, Illicium anisatum,
Cleyera japonica and Cinnamomum japonicum) had strong
correlations between Pmax and nitrogen concentration. Tall
trees tended to have larger variations in nitrogen concentration
and consequently in Pmax than small trees. However, the regression lines did not indicate large differences among species. For each species, the regression line tended to have a negative y-intercept, indicating that PNUE decreases with
decreasing nitrogen concentration (Table 2). Most species
showed a significant correlation for the relationship between
Pmax and RuBPCase concentration per unit leaf area (Figure 3), but differences among species were not large. Unlike
the Pmax–N relationship, there was no tendency for negative
TREE PHYSIOLOGY VOLUME 20, 2000
PNUE IN COEXISTING SPECIES
Figure 1. Characteristics of sun leaves of eight species plotted against
leaf life span. Mean and SD (n = 4–6) are shown for each species.
Species were Quercus acuta, Camellia japonica, Castanopsis sieboldii, Illicium anisatum, Cleyera japonica, Neolitsea sericea, Maesa
japonica and Cinnamomum japonicum in order of increasing leaf life
span. (a) In situ photosynthetic capacity per unit leaf area, (b) leaf nitrogen concentration per unit area, (c) leaf nitrogen concentration per
unit mass, (d) leaf mass per area, and (e) photosynthetic nitrogen use
efficiency (PNUE).
y-intercepts in the RuBPCase–N relationship (Table 2). Most
species showed a strong correlation between RuBPCase concentration and nitrogen concentration (Figure 4), but differences among species were not large. This relationship tended
to have a negative y-intercept (Table 2).
We also examined possible causes of variation in PNUE
among species by analyzing PNUE as the product of Pmax per
1251
Figure 2. Relationships between photosynthetic capacity and leaf nitrogen concentration in eight species: (a) Castanopsis sieboldii, (b)
Quercus acuta, (c) Camellia japonica, (d) Cleyera japonica, (e) Cinnamomum japonicum, (f) Neolitsea sericea, (g) Illicium anisatum, (h)
Maesa japonica, and (i) pooled data for all species. See Table 2 for regression coefficients.
unit RuBPCase and RuBPCase per unit nitrogen. To avoid the
confounding effect caused by PNUE decreasing with decreasing nitrogen concentration (cf. Table 2), we calculated Pmax at
0.1 mol N m –2 (P0.1N) from the regression. Similarly, RuBPCase concentration at 0.1 mol N m –2 (R0.1N) was determined. For
the relationship between Pmax and RuBPCase concentration, a
simple ratio of Pmax to RuBPCase was used (P/R). In Figure 5,
P/R and R0.1N are plotted on the ordinate and abscissa, respectively, with PNUE as contour lines. The P/R ratio varied from
3.7 (Camellia japonica) to 5.6 (Illicium anisatum). The value
of R0.1N varied from 0.98 (Quercus acuta) to 1.44 (Cleyera japonica) g m –2. Differences in P/R and in R0.1N among species
were 1.51- and 1.47-fold, respectively. Across eight species
Table 2. Regression coefficients.
Species
Castanopsis sieboldii
Quercus acuta
Camellia japonica
Cleyera japonica
Cinnamomum japonicum
Neolitsea sericea
Illicium anisatum
Maesa japonica
Pmax–N
Pmax–RuBPCase
RuBPCase–N
Slope
Intercept
Slope
Intercept
Slope
Intercept
74.1
88.6
86.1
78.8
57.1
33.8
47.6
57.1
–1.55
–4.45
–4.47
–1.00
–1.22
–0.21
0.47
–0.65
4.88
6.68
3.83
5.65
1.91
2.44
1.42
5.04
0.87
–1.94
–0.07
–0.14
2.52
–1.46
2.50
–0.94
14.0
14.0
19.9
18.9
20.7
27.1
26.2
17.5
–0.25
–0.42
–0.81
–0.44
–1.01
–1.27
–1.24
–0.38
TREE PHYSIOLOGY ON-LINE at http://www.heronpublishing.com
1252
HIKOSAKA AND HIROSE
Figure 5. Relationships between photosynthetic capacity per unit
RuBPCase (P/R) and RuBPCase concentration at 0.1 mol N m –2
(R0.1N). Photosynthetic rates at 0.1 mol N m –2 (P0.1N) are shown as
contour lines. Abbreviations: Cs, Castanopsis sieboldii; Qa, Quercus
acuta; Ca, Camellia japonica; Cl, Cleyera japonica; Ci, Cinnamomum japonicum; Ns, Neolitsea sericea; Ia, Illicium anisatum; Mj,
Maesa japonica.
Figure 3. Relationships between photosynthetic capacity and
RuBPCase concentration in eight species: (a) Castanopsis sieboldii,
(b) Quercus acuta, (c) Camellia japonica, (d) Cleyera japonica, (e)
Cinnamomum japonicum, (f) Neolitsea sericea, (g) Illicium anisatum, (h) Maesa japonica, and (i) pooled data for all species. See Table 2 for regression coefficients.
there was no significant correlation between P/R and R0.1N.
To analyze further the dependence of Pmax on leaf life span
we examined P/R, R0.1N and the RuBPCase concentration of
sun leaves as a function of leaf life span (Figure 6). The
RuBPCase concentration was significantly correlated with
leaf life span, whereas P/R and R0.1N were not. Neither P/R nor
R0.1N was correlated with leaf mass per area, nitrogen concentration per unit area, or nitrogen concentration per unit mass
(P > 0.1, data not shown).
Discussion
Figure 4. Relationships between RuBPCase and nitrogen concentration in eight species: (a) Castanopsis sieboldii, (b) Quercus acuta, (c)
Camellia japonica, (d) Cleyera japonica, (e) Cinnamomum japonicum, (f) Neolitsea sericea, (g) Illicium anisatum, (h) Maesa japonica,
and (i) pooled data for all species. See Table 2 for regression coefficients.
Photosynthetic capacity was negatively correlated with leaf
life span (Figure 1a), as has been shown in previous studies
(e.g., Chabot and Hicks 1982, Reich et al. 1991). However, the
causes of low Pmax in species with long leaf life spans differed
from those in previous studies. Reich et al. (1991) compared
23 Amazonian tree species and showed that PNUE decreased
with increasing leaf life span, whereas nitrogen concentration
was independent of leaf life span. We found that nitrogen
(Figure 1b) and RuBPCase (Figure 6c) concentrations per unit
leaf area tended to decrease with increasing leaf life span,
whereas PNUE did not depend on leaf life span (Figure 1).
Reich et al. (1991) showed that leaf life span was correlated
negatively with leaf nitrogen per mass and positively with leaf
mass per area. In contrast, we found that neither leaf mass per
area nor leaf nitrogen per mass was correlated with leaf life
span (Figure 1).
The discrepancies between our results and those of Reich et
al. (1991) may be associated with the smaller range of leaf life
spans and smaller number of species in our study (Reich
1993). Alternatively and perhaps more likely, the discrepancies may have resulted from the different criteria used to select
TREE PHYSIOLOGY VOLUME 20, 2000
PNUE IN COEXISTING SPECIES
Figure 6. (a) Photosynthetic capacity per unit RuBPCase (P/R), (b)
RuBPCase concentration at 0.1 mol N m –2 (R0.1N), and (c) RuBPCase
concentration per unit leaf area plotted against leaf life span.
the study species. Reich et al. (1991) compared tropical rain
forest species growing in different habitats. Differences in leaf
characteristics of the species were related to their native habitats (mainly nitrogen availability of soil) and successional
stages. Late-successional species and species growing in nitrogen-poor habitats tend to have low Pmax, low PNUE, long
leaf life span and high leaf mass per area (Reich and Walters
1994, Reich et al. 1994, Ellsworth and Reich 1996). On the
other hand, differences in the Pmax–N relationship among species occurring at similar habitats were small compared with
differences among species from different habitats or
successional stages (Reich and Walters 1994, Reich et al.
1994, Ellsworth and Reich 1996). Hirose and Werger (1994)
compared Pmax–N relationships among dominant and subordinate species coexisting in a herbaceous stand and showed that
the relationship differed little among species. They suggested
that similar resource-use efficiency is necessary for species to
coexist in a single stand (Hirose and Werger 1994, 1995). Results from these studies suggest that photosynthesis–nitrogen
relationships are more similar among species coexisting in a
single habitat than among species from different habitats.
An optimality model of leaf life span suggests that leaves
1253
with low Pmax should maintain photosynthetic activities for a
longer time than leaves with high Pmax to compensate for their
construction costs and thereby maximize whole-plant photosynthesis (Kikuzawa 1991). According to this model, the differences in leaf life span observed by Reich et al. (1991) may
be caused by differences in PNUE (and leaf mass per area).
Species with low PNUE, which caused low Pmax, would need a
longer leaf life span than species with high PNUE. On the
other hand, the differences in leaf life span in our study may be
caused by differences in leaf nitrogen concentration. Species
with low leaf nitrogen concentration, which caused low Pmax,
would need a longer leaf life span than species with a high leaf
nitrogen concentration. Thus, low Pmax explained the long leaf
life span in both studies, but low Pmax was caused by low
PNUE in the plants studied by Reich et al. (1991) and by low
leaf nitrogen concentration in our plants.
Although PNUE varied over a narrow range and showed no
correlation with leaf life span in the present study, species had
different PNUE values. Physiological causes of species variation in PNUE were analyzed. To avoid the confounding effect
of varying leaf nitrogen concentration on PNUE (Figure 2),
Pmax at 0.1 mol N m –2 (P0.1N) was calculated from the regression of Pmax on leaf nitrogen concentration. We then analyzed
P0.1N as the product of Pmax per unit RuBPCase (P/R) and
RuBPCase concentration at 0.1 mol N m –2 (R0.1N). Differences
in P/R and R0.1N among species were 1.51- and 1.47-fold, respectively (Figure 5), resulting in a twofold difference in
PNUE. Species differences in P/R and R0.1N were smaller than
in PNUE. We conclude that coexisting species would have
narrower ranges of P/R and R0.1N, and consequently of PNUE,
than species from different successional stages.
The P/R ratio varied from 3.7 to 5.6 (Figure 5). These values
are consistently lower than those of herbaceous species, e.g.,
8.9, 11.1 and 6.9 in rice, wheat (Makino et al. 1988) and
Chenopodium album L. (Hikosaka et al. 1998), respectively.
Values of R0.1N varied from 0.98 to 1.44 g m –2 (Figure 5). Assuming that 16% of leaf protein mass is nitrogen, the fraction
of leaf nitrogen allocated to RuBPCase was 11.2–16.5%.
Varying allocation of nitrogen to RuBPCase has been reported
for herbaceous species (Evans 1989). For example, wheat and
rice allocated 25–35% nitrogen to RuBPCase, whereas spinach allocated 13–25% (Makino et al. 1992). The R0.1N of spinach calculated from Makino et al. (1992) was about 15%,
which is comparable with the value obtained in our study.
These results suggest that differences in R0.1N among species
observed in the present study were small compared with those
observed among herbaceous species.
Although the mechanisms underlying the differences in P/R
and in R0.1N are of interest, we do not have any related information. There were no significant correlations between P/R and
R0.1N (Figure 5), or between these components and the ecological characteristics of leaves. Our results are not consistent with
the findings of Poorter and Evans (1998) who suggested that
allocation of nitrogen to RuBPCase is low in species with high
leaf mass per area. Although we cannot explain this discrepancy, we note that relationships between PNUE and other leaf
TREE PHYSIOLOGY ON-LINE at http://www.heronpublishing.com
1254
HIKOSAKA AND HIROSE
characteristics may differ depending on the criteria used to select the study species. Further studies are necessary to elucidate the physiological mechanisms underlying differences in
PNUE among species.
Acknowledgments
We thank Drs. A. Sakai, H. Nagashima and D. Nagamatsu, and
H. Kimura, T. Kimura, T.P. Yamano and K. Miyazawa for help in
field measurements. We also thank the members of the Tokyo University Forest in Chiba. This study was supported in part by grants from
the Japan Ministry of Education, Science and Culture (Nos. 08740593
and 09740574).
References
Ackerly, D.D. and F.A. Bazzaz. 1995. Leaf dynamics, self shading
and carbon gain in seedlings of a tropical pioneer tree. Oecologia
101:289–298.
Chabot, B.F. and D.J. Hicks. 1982. The ecology of leaf life spans.
Annu. Rev. Ecol. Syst. 13:229–259.
Chazdon, R.L. and C.B. Field. 1987. Determinants of photosynthetic
capacity in six rainforest Piper species. Oecologia 73:222–230.
Epron, D., D. Godard, G. Cornic and B. Genty. 1995. Limitation of
net CO2 assimilation rate by internal resistances to CO2 transfer in
the leaves of two tree species (Fagus sylvatica L. and Castanea
sativa Mill). Plant Cell Environ. 18:43–51.
Ellsworth, D.S. and P.B. Reich. 1996. Photosynthesis and leaf nitrogen in five Amazonian tree species during early secondary succession. Ecology 77:581–594.
Evans, J.R. 1989. Photosynthesis and nitrogen relationships in leaves
of C3 plants. Oecologia 78:9–19.
Field, C. and H. Mooney. 1986. The photosynthesis–nitrogen relationship in wild plants. In On the Economy of Form and Function.
Ed. T.J. Givnish. Cambridge Univ. Press, Cambridge, pp 25–55.
Hikosaka, K., Y.T. Hanba, T. Hirose and I. Terashima. 1998. Photosynthetic nitrogen-use efficiency in woody and herbaceous plants.
Funct. Ecol. 12:896–905.
Hikosaka, K., I. Terashima and S. Katoh. 1994. Effects of leaf age, nitrogen nutrition and photon flux density on the distribution of nitrogen among leaves of a vine (Ipomoea tricolor Cav.) grown
horizontally to avoid mutual shading of leaves. Oecologia 97:
451–457.
Hirose, T. and M.J.A. Werger. 1994. Photosynthetic capacity and nitrogen partitioning among species in the canopy of a herbaceous
plant community. Oecologia 100:203–212.
Hirose, T. and M.J.A. Werger. 1995. Canopy structure and photon
flux partitioning among species in a herbaceous plant community.
Ecology 76:466–474.
Kikuzawa, K. 1991. A cost–benefit analysis of leaf habit and leaf longevity of trees and their geographical pattern. Am. Nat. 138:
1250–1263.
Lloyd, J., J.P. Syvertsen, P.E. Kriedemann and G.D. Farquhar. 1992.
Low conductances for CO2 diffusion from stomata to the sites of
carboxylation in leaves of woody species. Plant Cell Environ.
15:873–899.
Loomis, R.S. 1997. On the utility of nitrogen in leaves. Proc. Natl.
Acad. Sci. 94:13,378–13,379.
Makino, A., T. Mae and K. Ohira. 1988. Differences between wheat
and rice in the enzymic properties of ribulose-1,5-bisphosphate
carboxylase/oxygenase and the relationship to photosynthetic gas
exchange. Planta 174:30–38.
Makino, A., H. Sakashita, J. Hidema, T. Mae, K. Ojima and B. Osmond. 1992. Distinctive responses of ribulose-1,5-bisphosphate
carboxylase and carbonic anhydrase in wheat leaves to nitrogen
nutrition and their possible relationships to CO2 transfer resistance.
Plant Physiol. 100:1737–1743.
Poorter, H. and J.R. Evans. 1998. Photosynthetic nitrogen-use efficiency of species that differ inherently in specific area. Oecologia
116:26–37.
Poorter, H., C. Remekes and H. Lambers. 1990. Carbon and nitrogen
economy of 24 wild species differing in relative growth rate. Plant
Physiol. 94:621–627.
Porra, R.J., W.A. Thompson and P.E. Kriedemann. 1989. Determination of accurate extinction coefficients and simultaneous equations
for assaying chlorophyll a and b extracted with four different solvents: verification of the concentration of chlorophyll standards by
atomic absorption spectroscopy. Biochim. Biophys. Acta 975:
384–394.
Reich, P.B. 1993. Reconciling apparent discrepancies among studies
relating life-span, structure and function of leaves in contrasting
plant forms and climates: “the blind men and the elephant retold.”
Funct. Ecol. 7:721–725.
Reich, P.B. and M.B. Walters. 1994. Photosynthesis–nitrogen relations in Amazonian tree species. II. Variation in nitrogen vis-a-vis
specific leaf area influences mass- and area-based expressions.
Oecologia 97:73–81.
Reich, P.B., M.B. Walters and D.S. Ellsworth. 1991. Leaf lifespan as
a determination of leaf structure and function among 23 Amazonian tree species. Oecologia 86:16–24.
Reich, P.B., M.B. Walters and D.S. Ellsworth. 1997. From tropics to
tundra: global convergence in plant functioning. Proc. Natl. Acad.
Sci. 94:13,730–13,734.
Reich, P.B., M.B. Walters, D.S. Ellsworth and C. Uhl. 1994. Photosynthesis–nitrogen relations in Amazonian tree species. I. Patterns
among species and communities. Oecologia 97:62–72.
Reich, P.B., B.D. Kloeppel, D.S. Ellsworth and M.B. Walters. 1995.
Different photosynthesis–nitrogen relations in deciduous hardwood and evergreen coniferous tree species. Oecologia 104:
24–30.
Sakai, A. and M. Ohsawa. 1993. Vegetation pattern and microtopography on a land slide scar of Mt. Kiyosumi, central Japan.
Ecol. Res. 8:47–56.
TREE PHYSIOLOGY VOLUME 20, 2000