沙漠研究 19-1, 25- 28 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

E. camaldulensis Optimal Planting Density in Desert Western Australia in View ofIts Photosynthetic Properties
Hajime UTSUGI1, Satoko KAWARASAKI2, Shin-ichi AIKAWA2, Hiroyuki TANOUCHI2,Nobuhide TAKAHASHI3, Hiroyuki HAMANO4, Toshinori KOJIMA5, Koichi YAMADA6
Abstract: The growth rate of Eucalyptus camaldulensis at an irrigated plantation in a semi-arid
area was same as at a non-irrigated plantation near the seashore (450 mmy-1 precip.). The Leaf
Area Index (LAI) and planting density at the former site (0.48, 207 trees ha-1) were less than at
the latter site (0.98, 1667 trees ha-1). We surveyed the photosynthetic properties of E.
camaldulensis at each site in the summer (dry) and winter (wet) seasons. The leaves were
found to have a higher Vcmax than the leaves of other tree species, and Vcmax did not differ
between the sites and seasons. Jmax for E. camaldulensis was near the median for investigatedtree species. The response of stomatal conductance to soil water potential did not differ
between the sites. These findings suggest that E. camaldulensis is highly light-demanding,which means that self-shading of leaves greatly reduces photosynthetic efficiency in the shaded
leaves. We conclude that the planting density under semi-arid conditions should be low, tokeep the LAI from exceeding 1. The estimated maximum stem and branch biomass production
is estimated to be about 3~5 Mg ha-1 y-1.
Key words: Eucalyptus camaldulensis, Planting density, Photosynthesis, Photosynthetic
efficiency, Semi-arid land

1. Introduction
In arid and semi-arid regions, drought conditions reduce plant growth. Toward afforesting suchregions, we must develop silvicultural techniques that guide the afforestation process from the present aridvegetation (Kojima et al., 2006), techniques that must be based on knowledge of the physiologicalprocesses that govern tree growth (Landsberg, 2003). Eucalyptus camaldulensis is the most widelydistributed eucalypt in Australia. The species excels among eucalypts in salt and drought tolerance (Daleand Dieters, 2007). We have tried to afforest semi-arid land with E. camaldulensis for carbon
sequestration at an irrigated experimental site (Site C) by water harvesting and hardpan blasting (Yamada etal., 2003, 2004). It is known that E. camaldulensis has significantly higher growth rate at a blasted area
than at a non-blasted area (Shiono et al., 2007). The leaves of E. camaldulensis tend to have constantVcmax values even at different area-based leaf nitrogen concentrations (Utsugi, 2006).
This paper compares the growth rate and photosynthetic capacity of E. camaldulensis at differentplanting densities under a given water condition. We discuss the optimal planting density in light of thephotosynthetic properties of the leaves.
2. Materials and Methods
The study was conducted at two experimental silvicultural sites for E. camaldulensis in WesternAustralia. One is Sturt Meadows pastoral station (STM, 28˚53’ S, 121˚45’ E) near the town of Leonora.
The mean annual precipitation is 200 mm y-1, most of which falls between April and August. We set up
the experimental site (Site C) near STM (Utsugi, 2006). The other is the Calingiri experimental site (SiteCalingiri; 31˚12’S, 116˚28’ E) near town of Northam, 120 km from the west coast.
The water supply at Site C corresponds to precipitation of approximately 500 mm y-1. The
precipitation at Site Calingiri is 450 mm y-1. The E. camaldulensis was planted at Site C and Site
Calingiri in June 1999 and June 2001, respectively. The respective planting densities are 207 and 1667
1

Hokkaido Research Center, Forestry and Forest Products Research Institute, Sapporo, Japan.
Forestry and Forest Products Research Institute, Ibaraki, Japan.
3
Department of Fine Materials Engineering, Shinshu Univ., Nagano, Japan.
4
National Institute for Environmental Studies, Ibaraki, Japan.
5
Department of Materials and Life Science, Seikei Univ., Tokyo, Japan.
6
The University of Tokyo, Japan.
226trees ha-1. At both study sites, the total nitrogen content in the soil was 0.1% at 5 cm in depth and 0.05%
at 25 cm in depth. The stem and branch biomass production was estimated using an allometric equation(Suganuma et al., 2006). The Leaf Area Index (LAI) at Site C was calculated from leaf biomass divided
by the mean of leaf mass per area (LMA) (307 g m-2, Utsugi et al., 2006) sampled in September 2003.
The LAI at Site Calingiri was measured using a canopy analyzer (LI-2000, Li-Cor Biosciences, Inc.,Nebraska, USA) in July 2006.
All gas exchange measurements were made with a portable steady-state photosynthesis system(Li-6400, Li-Cor Biosciences, Inc.). The experiment was done in winter (June to September) and summer(November to March) at each experimental site. We selected 5 to 9 fully expanded leaves formeasurement. We measured the leaf photosynthesis response to leaf intercellular CO2 concentration(A-Ci) between 06:00 and 10:00. Before measuring A-Ci, all leaves for measuring were shielded fromdirect sunlight to keep the leaf temperature from increasing. Leaves were acclimated in a chamber for atleast 10 min at 20~25 degrees. The temperature in the chamber was set according to the air temperature.
For the plotting of A-Ci curves, the light in the chamber was maintained at 1500 μmol m-2 s-1 ofphotosynthetic photon flux density. We measured the photosynthetic rate at the CO2 concentrations of360, 200, 360, 500, 1500, 1200, 300, 200 and 50 μmol mol-1 in the chamber. During the gas exchange
measurement for the A-Ci curve, the leaf to air vapor pressure deficit (L-VPD) in the chamber was kept
below 1.2 kPa and the leaf temperature was held between 20~25 degrees. Stomatal conductance during
the measurement was found to exceed 0.1 mmol m2 s-1. This procedure avoided the risk of stomatal
patchiness. Maximal ribulose-1,5-bisphosphate carboxylase (rubisco) activity (Vcmax) and maximal
electron transport mediated RuBP regeneration capacity (Jmax) were calculated using a biochemical model(Farquhar et al., 1982). These values were converted to 25-degree values (Vcmax25 and Jmax25) using anequation of temperature dependence (Kosugi, 2003). Following the gas exchange measurements,mass-based nitrogen concentration (Nm, %) and area-based nitrogen content (Na, N gm-2) were measured
for the sample leaves. The hourly changes in photosynthesis for one day and predawn leaf water potential
were measured at each site and at a natural forest stand (Site LP) near Site C (Utsugi et al., 2006). The
response of stomatal conductance (Gs) to net photosynthesis (An), relative humidity at the leaf surface(RHs) and leaf surface CO2 concentration (Cs) was calculated using the Ball-Berry empirical stomatal
conductance model (Ball et al. 1987).
Gs=m×An×RHs/Cs +Gsmin(1)
Where Gsmin and m are the intercept and slope obtained from least-squares regression. All statisticalanalyses were conducted using Statistica 5.0J, and means are reported ± standard error.
3. Results and Discussion
For the fifth year after planting, the annual stem and branch growth rate (GRSB) was the same for Site
C (4.5 ± 0.32 Mg ha-1 y-1) and Site Calingiri (4.2 ± 0.6 Mg ha-1 y-1). The LAI at Site C and Site Calingiri
were 0.47 ± 0.02 and 0.93 ± 0.04 respectively (Fig. 1). Even if the planting density at Site C increasedsuch that LAI rose to 1, the GRSB could not be expected to increase remarkably.
The mass-based nitrogen concentration (Nm) did not differ among the seasons nor among the study
6GRSB

Calingiri Summer
Calingiri WinterSiteC Summer
SiteC Winter110

4Vcmax (μmolm-2s-1)-1 -1

GRSB (Mgha y ) or LAI

120LAI532
110090807060500Site CSite Calingiri

PlaceFig. 1. Annual growth rate (GRSB) and LAI for
the fifth year after planting at Site Cand Site Calingiri. The error bar isstandard error.

40
0

12

3

4

56Na (gm-2)

Fig. 2. Na vs. Vcmax at Site C and Site Calingiri insummer (triangles) and winter (circles).

27sites (p>0.1). Na at Site Calingiri varied with season, andVc 25
the mean Na at Site Calingiri is smaller than at Site CJ 25(p<0.01, Fig. 2). These differences result from variationsin the LMA. The same variations in Na and LMA wererecognized in natural-growth E. camaldulensis (Utsugi et al.,2006). Vcmax25 and Jmax25 did not differ between sites nor
between the seasons (p>0.1, Fig. 3). The average Vcmax25
and Jmax25 were 77.4 ± 2.1 μmol m-2 s-1 and 120.0 ± 2.9μmol m-2 s-1, respectively. Among the tree species forPlace(Season)
which Vcmax25 and Jmax25 have been determined, the mean Fig. 3. Vc 25 (white bars) and J 25maxmax
Vcmax25 for E. camaldulensis determined in this study is(gray bars) at Site C and Site
86% that for the tree species with the highest Vcmax25
Calingiri for the summer(S) and(excluding the outlier, E. pauciflora) (Fig. 4), and the mean
winter(W) seasons.
Jmax25 of E. camaldulensis was 54% that for the tree species
with the highest mean Jmax25 (Fig. 5). Vcmax is the140
E. pau ciflora
maximum rate of RuBP carboxylation under saturated light120
Maxat low intercellular CO2 concentration. Higher Vcmax25100E. camaldulensis
indicates that E. camaldulensis is highly light-demanding
80for a C3 tree species. Jmax is the maximum rate of electron
60
Mintransport, which represents the potential quantum yield from40
photosynthesis. The Jmax25 for E. camaldulensis puts it
20near the median among C3 tree species. This indicates that
00102030
405060the leaves under shade condition cannot have a higher
Tree species No.
photosynthetic rate than species having higher Jmax25. Thehigher LAI in E. camaldulensis forest hinders Fig. 4. Vcmax values of tree species
investigated so far. Black circles
photosynthetic production per unit leaf area at the standare Vcmax value of each species
level, because of self-shading of leaves.
put in low order from left side.
We assume that predawn leaf water potential is equal to
White circles are those of othersoil water potential. There are pronounced seasonal
eucalypts.
patterns in parameter m and Gsmin, as shown by Equation (1).
250
E. pau ciflora
The parameters decrease when predawn leaf water potential
E. camaldulensis
200
decreases in the range of -0.5 to -3.5 MPa (Figs. 6 and 7).
MaxIn contrast, in a study of Mediterranean blue oak, mPinus
150
Acer
remained constant even when the predawn leaf water
Nyssa
PopulusQuercus100
potential decreased (Xu and Baldocchi, 2003); however, in
Kalopanax
Avicennia
PrunusMin Betulastudies of other Mediterranean trees (e.g. Sala andQuercus
50Poplus
Tenhunen, 1996), m did vary with changes in predawn leaf
0water potential. Despite the different water conditions
051015202530
Tree species No.
among Site C, Site LP and Site Calingiri, the relations inEquation (1) seem to be approximated with one power
Fig. 5. Jmax values of tree species
function (Figs. 6 and 7). These findings indicate that theinvestigated so far. Black circles
response of stomata to water stress in E. camaldulensis does
are Jmax value of each species
not differ even when the planting density differs. In
put in low order from left side.
White circles are those of othermanaging the stand planting of E. camaldulensis undereucalypts.
shade condition, where photosynthesis is highly
light-demanding and inefficient, we should focus on
preventing the self-shading of leaves. The standard planting density in semi-arid condition should be set
such that the leaf area index does not exceed 1. At such a planting density, stem and branch biomass
production is about 3~5 Mg ha-1 y-1.
100

160max140max

120
100

60

80

4060
40Jmax 25 (μmolm-2s-1)-2 -1
Vcmax25 (μmolm s )80

202000J max25(μmolm-2s-1)-2 -1

Vc max 25(μmolm s )Calingiri(S) Calingiri(W)SiteC(S)SiteC(W)

Quercus
Nyssa
Populus
Prunus

Pinus
Picea
Acer

○Eucalyptus

BeturaPopulus
Kalopanax
Fraxinus
Avicennia○Eucalyptus

4. Conclusions
E. camaldulensis planted on an irrigated semi-arid site (Site C) and on a non-irrigated plantation site28
140.05Site C and Site LP
Site Calingiri

12Site C and Site LP
Site Calingiri

10m

]¥

Gsmin (molH2Om-2s-1)

0.04

y=10.6×exp (0.4×x)r2=0.5886

y=0.05×exp (0.7×x)r2=0.89

0.03

0.02

0.01

40.00

20.0-0.5-1.0-1.5-2.0-2.5

-3.0

-3.5

Predawn leaf water potential (MPa)Fig. 6. m vs. predawn leaf water potential. The“m” is determined in Equation (1).

0.0-0.5

-1.0

-1.5

-2.0

-2.5

-3.0-3.5

Predawn leaf water potential (MPa)Fig. 7. Gsmin vs. predawn leaf water potential. The“Gsmin” is determined in Equation (1).

(Site Calingiri) were compared in terms of stem and branch growth rate (GRSB) and photosyntheticproperties. Planting density and LAI (LAI=1) were higher for Site Calingiri than for Site C. GRSB andphotosynthetic capacity (Vcmax25 and Jmax25) did not differ significantly between the sites. E.
camaldulensis is highly light-demanding, showing high Vcmax (86% of the Vcmax for the C3 tree species withthe highest mean Vcmax). The response of stomatal conductance to soil water content does not differ
greatly between the sites. These findings indicate that silvicultural techniques for afforestation of E.
camaldulensis in semi-arid areas should keep the LAI below 1, because this will prevent the self-shading ofleaves. Under such LAI, the GRSB is estimated to range from 3 to 5 Mg ha-1 y-1.
Acknowledgements
I wish to thank H. Tobita, S. Kitaoka and A. Uemura for providing critical comments. This study was
supported by a grant from Mitsui & Co., Ltd. Environment Fund and by the Global Environment Research
Fund of the Ministry of the Environment (GHG-SSCP Project).
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