Journal of Environmental Science and Management 60-67 (Special Issue 1-2012)
ISSN 0119-1144
60
Effects of Light Intensities on Growth Performance, Biomass Allocation and
Chlorophyll Content of Five Tropical Deciduous Seedlings in Lao PDR
Chanhsamone Phonguodume1, Don Koo Lee2, Silavanh Sawathvong3, Yeong Dae Park4*, Wai Mun
Ho5 and Edwin A. Combalicer6
ABSTRACT
Growth performance, biomass allocation and chlorophyll content of Afzelia xylocarpa Craib, Anisoptera
costata Korthals, Dalbergia cochinchinensis Pierre, Dipterocarpus alatus Roxb.& G.Don and Hopea odorata Roxb.
seedlings were compared under different light intensities (100%, 50-70% and 30-50%) in Lao PDR. Results showed
that all species had survival rate above 94% under all light intensity treatments. Root collar diameter growth (RCD)
varied significantly among the five species (F=10.91, P=0.0018). Afzelia xylocarpa had significantly higher RCD
than other species while A. costata and D. cochinchinensis showed higher RCD under higher light intensity. Height
was also affected significantly by light intensities among the species tested (F=4.85, P=0.0223). A. xylocarpa showed
better height growth at lower light intensity. The number of leaves showed significant differences among species
(F=9.191, P=0.004) but was not significantly different among light intensities (p<0.05). Biomass allocation was
not significantly different within and among species (F=3.39, P=0.0665) under different light intensities (F=2.72,
P=0.096). Both A. xylocarpa and D. alatus accumulated higher total biomass under 50-70% light intensity compared
to other light conditions. Hopea odorata showed increasing biomass with increasing light intensity but A. costata
accumulated more biomass at lower light intensity. The experiment also found that total chlorophyll content was
significantly different among species (p<0.05). This study showed that each species had different adaptations to light
conditions that should be considered in nursery practice for optimum growth of seedlings.
Key words: biomass, chlorophyll content, growth, light intensity, tropical deciduous seedlings
INTRODUCTION
Tropical rainforests could be influenced by the
surrounding vegetation and habitat environment, such as
light and temperature, in their ecological and physiological
responses (Henmann and Hugh 2010; Wright 2005). In a
tropical deciduous forest, more light exists as it has a thinner
canopy which produces more undergrowth. There are also
seasonal changes as the light and temperature shift just
enough to trigger the trees to drop their leaves (Johnson
2009). However, light environment in degraded secondary
forests may be diverse because light condition changes by
forest structure such as gap formation and time span after
disturbance (Mesquita 2000; Whitmore 1998). Light is the
main factor covered in the studies of environmental responses
of dipterocarp and other tropical tree species (Norisada and
Kojima 2005).
Light plays an important role in the development of
a plant. Processes such as photosynthesis and phototropism
depend on the availability of light sources for plants (Long
2011). Plant seeks out light sources for energy and survival.
Light is one of the most important environmental factors
affecting plant establishment and growth in a tropical
deciduous forest. Plant performance is enhanced through
morphological and physiological acclimation to light
environment (Kozlowski and Pallardy 1996). It is also an
important factor in forest regeneration and growth.
The tropical species are unique in vegetation and habitat
as they adapt to varying light intensities. The role of light
in the life of a plant is much more complex than the plant
sitting in the sun for a whole day. Shade environment or light
intensity limits the photosynthetic capacity and biomass of
a plant. Growth analyses of tree seedlings under controlled
conditions indicate how plants adjust to light environment
(Poorter 2001; Popma and Bongers 1988). Leaves under
shade conditions have higher chlorophyll content and lower
leaf mass per area (LMA) so as to maintain the low light
compensation point (Lambers, Chapin and Pons 1998). Plants
absorb light energy and transfer it into the photosynthetic
apparatus (Sims and Gamon 2002). Healthy plants capable
of maximum growth are generally expected to have larger
amounts of chlorophyll than unhealthy ones.
A better understanding of ecological traits such as
Ph.D. Candidate, Department of Forest Sciences, Research Institute for Agriculture and Life Sciences, College of Agriculture and Life Sciences, Seoul National University
and Director, Forest Research Center, National Agriculture and Forestry Research Institute, Ministry of Agriculture and Forestry, Vientiane Capital, Lao PDR P.O. Box:
7174
2
Professor, Department of Forest Sciences, Research Institute for Agriculture and Life Sciences, College of Agriculture and Life Sciences, Seoul National University
3
Director General, Department of Forestry, Ministry of Agriculture and Forestry, Vientiane Capital, Lao PDR P.O. Box: 7174
4
Research Professor, Department of Forest Sciences, Research Institute for Agriculture and Life Sciences, College of Agriculture and Life Sciences, Seoul National
University, 599 Gwanangno, Gwanak-gu, Seoul, 151-921, Republic of Korea. E-mail: [email protected] (*corresponding author)
5
Researcher, Forest Research Institute Malaysia, 52109 Kepong, Selangor Malaysia
6
Assistant Professor, College of Forestry and Natural Resources, University of the Philippines Los Banos, 4031 College, Laguna, Philippines
1
Journal of Environmental Science and Management (Special Issue 1-2012)
61
strong light tolerance for the target species could improve
techniques for enrichment planting in secondary forests
(Appanah and Weinland 1993; Kenzo et al. 2008;
Krishnapillay 2002). It is therefore necessary to consider
specific species favorable to be planted in light conditions
when conducting effective enrichment planting in degraded
secondary forests. This will be very useful in managing
mixed plantation forests and in rehabilitating degraded
areas of the country. However, there are limited information
about the effect of light intensities on growth and biomass
allocation of tree species. Thus, the objective of this study
was to determine the effects of light intensities on growth,
biomass allocation and chlorophyll content of selected native
species in tropical deciduous forest of Lao PDR.
Biomass (roots, stem, and leaves) was determined in
one-year-old seedlings of the five tropical deciduous species.
Thirty healthy (30) seedlings were randomly selected for
each species in every treatment for determination of fresh
weight and total dry biomass. Samples were placed in paper
bags for transferring to the laboratory. The root, stem and
leaf samples were oven dried at 80oC for 48 to 72 hours until
constant weight.
MATERIALS AND METHODS
Chlorophyll content
Site description
The chlorophyll content (a, b and total) was obtained
by collecting five leaf samples in each species for every
treatment. A single-hole puncher was used to get the samples.
The samples were then put into vial with 10 mL 80% acetone
to extract the chlorophyll. The extracts were kept in the
dark at 4oC for seven days. The absorbance of extracts was
read at wavelengths of 663 nm and 645 nm using Hitachi
U-1000 Spectrophotometer (Shimadzu Co., Japan) in the
Department of Chemistry, Faculty of Sciences, National
University of Lao PDR. Arnon’s equation (Arnon 1949) was
used to calculate the chlorophyll content (a, b, and total)
as shown below. Unlike other methods which use solvents
like Dimethyl Formamide (DMF) and Dimethyl Sulfoxide
(DMSO), the use of acetone in Arnon’s method is not toxic
to human as it is not easily absorbed by the skin.
(1) Chlorophyll a ( g/mL-1) = 12.7 A663 – 2.59 A645
(2) Chlorophyll b ( g/mL-1) = 22.9 A645 – 4.67 A663
(3) Total chlorophyll ( g/mL-1) = 8.05 A663 + 20.29 A645,
where: A 663 is the absorbance at 663 nm; and A645 is the
absorbance at 645 nm.
The study was conducted in the nursery of Forestry
Research Centre, National Agriculture and Forestry Research
Institute, Lao` PDR. It is located between 18o 15’ 32’’ N longitude
and 102o 33’ 24’’ E latitude with an altitude of 195 m above
sea level. The average annual precipitation is 1,990 mm from
2000 to 2008 and was moderately seasonal in distribution. The
average air temperature is 27oC with the lowest in December
(23.5oC) and highest in May (30.5oC). Relative humidity is
lowest in February (69%) and highest in August (84%).
Study species and planting materials
The seeds of five tropical deciduous species,
namely Afzelia xylocarpa, Anisoptera costata, Dalbergia
cochinchinensis, Dipterocarpus alatus, and Hopea odorata
were collected from identified natural seed sources in Lao
PDR. Planting materials used were plastic pots (12 cm in
diameter x 18 cm in height) and mixture of planting medium
with a ratio of 2:1:2:2 for soil, sand, rice husk (biochar)
and manure, respectively. Seedlings were transplanted
from seed germination bed to plastic bag containers two
weeks after germination. Seeds were germinated based on
the recommended germination procedure for each species.
Seedlings were nursed for another two weeks by removing
weeds and constant application of water to ensure seedlings
survival before treatment application in May 2007.
A Completely Randomized Design (CRD) was
employed for this study with five species and three treatments
of light intensity at 100% (control), 50-70% and 30-50%. A
total of 1,500 (100 seedlings per treatment for each species)
were used for the study.
Growth performance
The growth performance of seedlings was assessed
using survival rate (%), root collar diameter (RCD, mm), total
height (cm) and number of leaves. These parameters were
measured every three months from June 2007 up to June 2008.
Biomass
Data analysis
The mean values and standard errors of growth
parameters, biomass, and chlorophyll content were analyzed
using MS Excel 2007 and SAS 9.1.3 for Windows 2007 (SAS
Institute Inc., USA). Duncan’s Multiple Range Test (DMRT)
was used for multiple comparisons of seedling performance
under different light intensities. The significance for all
analysis was determined at p<0.05.
RESULTS AND DISCUSSION
Tree species used in the study
Two legumes (Afzelia xylocarpa Craib and Dalbergia
cochinchinensis Pierre.) and three dipterocarp (Anisoptera
cossta Korth., Dipterocarpus alatus Roxb., and Hopea
Effects of light intensities
62
odorata Roxb.) were used for the study. The selected species
have wide ranges of ecological adaptations. For instance,
most dipterocarp species are shade tolerant while the legumes
are light demanding. The species in this experiment are also
highly known for their high quality timber and non-timber
products (Table 1).
Growth performance
Survival rate
Most of the species showed high survival rates of over
94% in all species and light treatments. Survival of all the
one-year-old seedlings within and among the species was
not affected by different light intensity treatments (Table 2).
This indicated that both legumes species (A. xylocarpa and
D. cochinchinensis) and dipterocarp species (Dipterocarpus
alatus, H. odorata and A. costata) performed similarly (p>0.05)
in terms of survival under the given light conditions. In a case
study at Barro Colorado Island of Panama, however, different
species (e.g. pioneer, shade tolerant, and intolerant, evergreen
or deciduous tree species) showed different responses to
light or gap dynamics (Kitajima 1994). In contrast, this study
showed that there were no significant differences in seedlings
survival grown under different light intensities.
Figure 1 shows that different light intensities resulted
in statistically different RCD among the species (F=10.91,
P=0.0018). Means of RCD showed significantly higher value
(p<0.05) in A. xylocarpa compared to other species probably
due to its ability, as a leguminous species, in nitrogenfixation that promoted better growth. This is followed by A.
costata and D. alatus. Dalbergia cochinchinensis recorded
the smallest mean with lower RCD at reduced light intensity.
The root collar diameter (RCD) of A. xylocarpa was
significantly higher than the other four species at all light
treatments. This indicates its suitability for planting in open or
under shade. The RCD of A. costata and D. cochinchinensis
were large under higher light intensity and decreased
with decrease in light intensity level. On the other hand,
the RCD for H. odorata and D. alatus were significantly
higher (p<0.05) under the moderate light condition (5070%). Among the five species studied, A. xylocarpa had
significantly thicker RCD (9.7-10.5 mm) while H. odorata
and D. cochinchinensis had thinner RCD (5.7-6.4 mm). The
maximum growth of tropical rainforest seedlings in Africa
was reported at 10-44% sunlight (Agyeman, Swaine, and
Thomption 1999) while another study showed 50-100%
sunlight for fast growing species and 25-50% shade for slow
growing species in Bolivia (Poorter 1999).
Height
Height was affected significantly by different light
intensities among the species tested (F=4.85, P=0.0223).
A. xylocarpa showed significantly (p<0.05) higher growth
at 79.40 cm and 78.20 cm in 30-50% and 50-70% light
intensities, respectively. However, H. odorata and A. costata
had taller height under higher light intensity and are therefore
suitable to be planted in the open. D. cochinchinensis
had almost similar height at all light intensity levels. On
the other hand D. alatus had taller height (39 cm) under
medium light intensity (Figure 2). In a study by Kenzo
et al. (2008) and Sack and Grubb (2002), they found that
light had effects on wood density and height of seedlings.
They observed that 35% of light condition was suitable for
seedling growth. Mesquita (2000) conducted a research to
compare five light intensities (100%, 89-90%, 50-60%, 2030% and 0% control). It was reported that in natural forests,
seedlings height grew to more than 25 cm under 50% light
intensity and one-fourth of the species grew to more than 25
cm year-1.
Number of leaves
The result also agrees with Agyeman, Swaine and
Thomption (1999) who showed that the number of leaves
showed strong relationships with species characteristics and
light. Table 3 shows the mean numbers of the leaves of the
five species grown under different light intensities. Dalbergia
cochinchinensis and A. xylocarpa showed significantly
higher number of leaves under all light intensities. Further,
D. cochinchinensis and A. xylocarpa had highest number of
leaves, 35 and 23, respectively, when grown at high light
intensity levels.
Biomass allocation
Light was reported to affect biomass allocation (Poorter
1999). Most of the studies had focused on growth rather than
biomass (Fetcher, Strain and Oberbauer 1983; King 1991;
Oberbauer and Strain 1985; Osunkoya et al. 1993; Popma
and Bongers 1991; Rincon and Huante 1993). AKECOP
(2010a) reported that total biomass (roots, stems and leaves)
of two-year-old Pterocarpus indicus were significantly
different among light intensities with 120 g in 100%, 63 g
in 65% and 59 g in 30%, respectively. In addition, biomass
allocation was found to be in order of leaves > stems >
roots. In this study, biomass allocation was not statistically
different at 5% level within and among the species (F=3.39,
P=0.0665) and among under different light intensities with
(F=2.72, P=0.096).
Under 100% light intensity, Dipterocarpus alatus had
the highest accumulation of total biomass (p<0.05) followed
by H. odorata (Table 4). These two species have thus shown
their possibility to grow under direct sunlight, for instance,
in the open areas of degraded sites for rehabilitation
purposes. Nonetheless, D. cochinchinensis and A. costata
Journal of Environmental Science and Management (Special Issue 1-2012)
63
Table 1. Ecological distribution, growth habit and economic importance of the species used in the study.
Family
Leguminosae
Dipterocarpaceae
Leguminosae
Species
Afzelia
xylocarpa
Ecological distribution
Native to Cambodia, Lao PDR, Myanmar,
Thailand and Vietnam; occurs in evergreen
and deciduous forests at 100-650 m
altitudes
Native to Cambodia, Lao PDR, Malaysia,
Anisoptera
Thailand and Vietnam; occurs in evergreen,
costata
moist or slightly dry forests, sometimes
gregariously growing in a pure stand at
altitudes up to 1000 m
Occurs in dry evergreen forests of
Dalbergia
cochinchinensis Cambodia, Lao PDR, Thailand and Vietnam
at altitudes up to 1000 m
Dipterocarpaceae
Dipterocarpus
alatus
Dipterocarpaceae
Hopea odorata
Growth habit
Tree up to 30 m tall and
150 cm in diameter; lightdemanding; deciduous;
endangered species
Large tree up to 30-40 m
and 50-100 cm in diameter;
endangered species
Deciduous tree up to 30 m
tall, 60-80 cm in diameter;
drought-tolerant but slow
growing; shade-tolerant
when young; vulnerable
species
Native to evergreen and deciduous forests
Large tree up to 40 m tall
of Cambodia, Lao PDR, Myanmar,
and 150 cm in diameter;
Philippines, Thailand, Vietnam, Bangladesh, shade-tolerant and fast
Andaman islands; occurs gregariously along growing; endangered
rivers at altitudes up to 500 m
species
Distributed in Cambodia, India, Lao PDR,
Large tree up to 30-40 m
Malaysia, Thailand, Vietnam; occurs
and 60-80 cm in diameter; it
gregariously in dense tropical evergreen
demands wet and deep soil;
forests, but after a long period of selective
natural regeneration is good
logging, it is only found in small groups or under thin forest-cover,
in solitude at altitudes up to 900 m
endangered species
Uses
Timber, food,
tanning, soil
improvement
Timber, resin
Timber, soil
improvement
Timber,
oleoresins,
medicine,
soil
improvement
Timber,
resins and
gums
Sources: Dung 1996; Lao Tree Seed Project 2003.
Figure 1. Root collar diameter of Afzelia xylocarpa, Anisoptera costata, Dipterorpus alatus, Hopea odorata and Dalbergia
cochinchinensis under different light intensities (the same letters are not significantly different by using DMRT
p<0.05).
Effects of light intensities
64
Figure 2. Height of Afzelia xylocarpa, Hopea odorata, Anisoptera costata, Dalbergia cochinchinensis and Dipterocarpus
alatus under different light intensities (the same letter are not significant difference among height using DMRT
p<0.05).
Table 2. Survival rate of seedling under different light
intensities (% of survival).
Species
Afzelia xylocarpa
Anisoptera costata
Dalbergia
cochinchinensis
Dipterocarpus alatus
Hopea odorata
Overall mean of
treatments
Light treatment
100% 50-70% 30-50%
96
100
100
96
100
100
98
100
99
Overall
mean of
species
96.7
100.0
99.7
94
96
97.2
96
97
97.8
94
99
98.0
94.7
97.3
97.7
Table 3. Number of leaves in one-year-old tropical deciduous
seedlings in the nursery.
Species
Afzelia xylocarpa
Anisoptera costata
Dalbergia cochinchinensis
Dipterocarpus alatus
Hopea odorata
100%
23 (5)a
12 (3)bc
35 (6)a
7 (1)c
20 (7)b
Light treatment
50-70%
30-50%
27 (9)a
25 (9)a
12 (2)bc
12 (2)bc
24 (2)a
26 (4)a
9 (2)c
9 (1)c
17 (4)b
15 (4)b
Notes: Value in parenthesis indicates standard errors; Different letters in columns
indicate significant difference among number of leaf using DMRT (p<0.05).
performed poorly in the strongest light intensity treatment.
Afzelia xylocarpa showed significantly higher (p<0.05)
total biomass under 50-70% light intensity among the five
species. Under this light treatment, A. xylocarpa as well
as D. alatus accumulated the highest biomass compared
to other light condition. Dalbergia cochinchinensis and A.
costata recorded the lowest biomass again under 50-70%
light intensity. Under the lowest light intensity treatment
(30-50%) A. xylocarpa accumulated significantly higher
(p<0.05) total biomass followed by D. alatus. This indicated
that both species preferred low to moderate light intensity
for optimum biomass production. Hopea odorata had the
lowest total biomass in 30-50% light intensity but showed
and increasing trend with higher light intensity.
Under 100% light intensity, H. odorata only showed
higher root biomass, stem and leaf. Dalbergia cochinchinensis
in 30-50% light intensity, Dipterocarpus alatus and A.
xylocarpa showed higher root, stems and leaves. While A.
costata showed different root biomass at 30-50%, stem at
100% and leaf at 50-70% light intensities. However, species
characteristic are optimum growth and biomass allocation
with different light intensities.
In a study by Montgomery and Chazdon (2002), 14month-old seedlings of three tropical species showed a strong
Journal of Environmental Science and Management (Special Issue 1-2012)
65
Table 4. Biomass allocation of one-year-old Hopea odorata (Hop), Dalbergia cochinchinensis (Dal), Dipterocarpus alatus
(Dip), Anisoptera costata (Ani) and Afzelia xylocarpa (Afz) grow in nursery under different light intensities.
Light treatment
100%
50-70%
30-50%
Component
Root
Stem
Leaf
Total
Root
Stem
Leaf
Total
Root
Stem
Leaf
Total
Ani
5.70 (1.46)c
5.60 (1.91)c
5.23 (0.81)b
16.54 (1.39)d
6.13 (0.83)c
5.51 (0.66)d
8.13 (0.85)b
19.77 (0.78)
7.01 (1.26)b
3.95 (2.84)d
6.89 (0.61)b
17.85 (1.57)c
Afz
6.72 (1.40)a
10.93 (2.16)b
3.18 (1.15)c
20.82 (1.57)c
15.99 (0.34)a
38.55 (0.61)a
6.27 (0.49)c
61.32 (0.48)a
12.16 (1.50)a
23.22 (1.86)a
4.98 (1.04)bc
40.36 (1.46)a
Dal
6.05 (0.76)c
6.34 (1.07)c
4.37 (0.45)b
16.76 (0.76)d
5.31 (0.61)c
6.17 (0.90)d
2.54 (0.33)d
14.02 (0.61)
6.28 (0.43)bc
7.69 (1.67)c
5.62 (0.81)b
19.59 (0.91)c
Dip
10.16 (0.60)b
15.35 (0.75)a
9.78 (0.43)a
35.29 (0.60)a
11.44 (1.88)b
22.48 (2.80)b
16.26 (1.20)a
50.18 (1.96)b
7.51 (0.51)b
10.23 (0.77)b
9.95 (0.82)a
27.67 (0.70)b
Hop
9.29 (2.27)c
12.01 (5.88)b
8.08 (1.04)ab
29.38 (3.06)b
4.29 (0.49)c
10.19 (0.68)c
7.55 (1.27)c
22.03 (0.81)c
3.37 (1.13)c
5.26 (1.05)cd
4.59 (0.62)bc
13.22 (0.93)d
Notes: Value in parenthesis indicates standard errors; Different letters in rows indicate significant difference among number of leaf using DMRT (p<0.05).
increasing in total biomass as light increased. However,
the strength of the growth response differed among species
causing a change in the rank order of species growth rates as
light availability increase. Poorter (2001) reported that 17% of
six tropical rain forest saplings had negative relative biomass
growth rates, although they occurred in fairly bright conditions.
Chlorophyll content
Table 5 shows the mean total chlorophyll content of
one-year-old tropical deciduous seedlings in different leaf
positions under 100% light intensity. In this study, total
chlorophyll content was significantly different (p<0.05)
among species. Dipterocarpus alatus showed highest
chlorophyll contents in all respective leaf positions among the
five species studied. The highest chlorophyll content in this
species was found in the middle leaf position. Meanwhile,
H. odorata and D. cochinchinensis had significantly higher
total chlorophyll contents in the lower position. In A.
xylocarpa the total chlorophyll content was highest in the
middle leaf position (1.06 g mL-1). The total chlorophyll
content is more depedent on physiological characteristics
of species than on light or shade condition (Minotta and
Pinzauti 1996). Cho et al. (2008) reported that chlorophyll
contents of five hardwood species in central temperate
zone of Korea were highest in 7-12% light intensity, while
lowest under 100% light intensity. Sun leaves (upper leaf)
grown under high irradiance possess higher photosynthetic
rates than shade leaves (Boardman 1977; Lichtenthaler
and Akoyunoglou 1981) but most of the leaves in shading
conditions have a high leaf area index. AKECOP (2010b)
reported that chlorophyll contents of different leaf positions
were significantly different in three one-year-old tropical
species in the Philippines with highest in lower leaf position
of Acacia auriculiformis, (11.5 g/mL-1) and A. mangium
(12.2 g/mL-1) and, in middle position of Pterocarpus indicus
(18.3 g/mL-1). Lee (2006) reported that chlorophyll contents
of four five-year-old species planted in the Philippines were
significantly different with different spacing (2 x 2 m, 4 x 4
m, 6 x 6 m) The results showed highest chlorophyll contents
in Erythrina orientalis (5.5 g/mL-1) and P. indicus (3.6 g/
mL-1) for 4 x 4 m, in Bischofia javanica (2.3 g/mL-1) for 6 x
6 m, and in Dracontamelon dao (2.2 g/mL-1) for 2 x 2 m.
Table 5.Total chlorophyll content of five species after oneyear of planting in nursery.
Species
Anisoptera costata
Afzelia xylocarpa
Dalbergia cochinchinensis
Dipterocarpus alatus
Hopea odorata
Upper
2.678
(0.84)a
0.994
(0.02)ab
1.086
(0.08)b
2.824
(0.78)b
1.067
(0.13)c
Leaf positions
Middle
1.738
(0.91)b
1.055
(0.07)a
1.044
(0.09)b
3.801
(0.06)a
1.249
(0.01)b
Lower
1.090
(0.07)c
0.692
(0.12)b
1.976
(1.15)a
2.842
(0.95)b
2.827
(0.90)a
Notes: Value in parenthesis indicates standard errors; Different letters in rows
indicate significant difference using DMRT (p<0.05).
Table 6 summarizes the parameters used in the five
study species under different light intensities. Among the light
intensity treatments, most of the species performed better in
50-70% light intensity such as H. odorata, D. alatus and A.
xylocarpa. Only D. cochinchinensis had good performance
in 30-50% light intensity. This means that 50-70% light
intensity is the optimum amount needed by the plant species
to survive and to obtain good performance in the field. The
presence of optimum light can have a direct bearing on the
plant’s rate of growth. A plant’s most natural habitat provides
the intensity of light needed for optimal growth. As a result,
different plant types may require different light intensities.
Effects of light intensities
66
Table 6. Summary of parameters used in the five species by score.
Species
SR RCD
3
3
3
2
3
3
3
2
3
1
Ani
Afz
Dal
Dip
Hop
Legend:
SR
RCD
H
Survival rate
Root collar diameter
Total height
L
W
Ch
100%
50-70%
30-50%
H L W Ch Total SR RCD H L W Ch Total SR RCD H L W Ch Total
3 3 1
3
16
3
2 1 3 3
2
14
3
2 2 3 2
1
13
1 1 1
2
10
3
3 2 3 3
3
17
3
3 3 2 2
1
14
2 3 2
2
15
3
2 2 1 1
1
10
3
1 3 2 3
3
15
2 2 2
1
12
3
3 3 3 3
3
18
3
1 2 3 1
2
12
2 3 3
1
13
3
3 3 2 2
2
15
3
2 1 1 1
3
11
Number of leaves
Biomass
Chlorophyll content
1
2
3
Detailed physiological effects of varying light intensities
were not determined in this study except for chlorophyll
contents. However, it can be inferred that light intensity
contributes greatly to plant physiological processes since
plant growth relies on a series of interactions that involve
the presence of light. For example, photosynthesis enables
plant metabolism processes to take place and provides the
energy that fuels these processes. Light intensity levels can
have a significant effect on photosynthesis rates, which
are directly related to a plant’s ability to grow. According
to Jeanty (2008), light intensity has something to do with
the amount of light energy made available to a plant, which
can vary according to color and the actual strength of the
light. In addition, plants are typically most responsive to
light that falls within the blue and red light ranges. In effect,
higher light intensities make more energy available for plant
photosynthesis processes to take place.
CONCLUSION
Light is an important factor in forest regeneration
and growth. Tropical deciduous tree species are unique
in vegetation and habitat and therefore light affects the
shade-tolerant species physiologically and biochemically.
Understanding light requirement is important to plant
physiology with regard to stress. In conclusion, the survival
was not significantly different within and among the species
in different light intensities, while the number of leaves, root
collar diameter, height and biomass allocation of seedlings
vary with light and species. The chlorophyll content of
each species in this study was also dependent on different
leaf positions (upper, middle and lower positions). Light
intensity between 50-100% was suitable for the growth of
one-year-old tropical deciduous in the nursery. The results of
this study can be applied in the nursery practice to produce
healthy seedlings for successful rehabilitation of degraded
tropical forests in Lao PDR.
Low
Medium
High
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This study was carried out with the support of "ASEANKorea Environmental Cooperation Project" provided by
Korea Ministry of Foreign Affairs and Trade. The authors
sincerely thank the staff of Forestry Research Centre of Lao
PDR, for their assistance throughout the experiment.
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