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Vol.%12(1):%113-131,%January%2024% %DOI:%https://doi.org/10.23960/jsl.v12i1.821%%%%%
Jurnal'Sylva'Lestari'
Journal%homepa ge:%https://sylvalestari.fp.unila.ac.id%
113
P-ISSN: 2339-0913
E-ISSN: 2549-5747
Full Length Research Article
Effects of Decapitation, Water-Deficit Stress, and Pot Size on Morpho-
Anatomy and Physiology of Pterocarpus indicus
Jonathan Ogayon Hernandez, Marilyn Sabalvaro Combalicer, Arthur Glenn Agojo Umali, Lerma San Jose
Maldia*
Department of Forest Biological Sciences, College of Forestry and Natural Resources, University of the Philippines Los Baños,
Los Baños, Philippines
* Corresponding Author. E-mail address: lsmaldia@up.edu.ph
ARTICLE HISTORY:
Received: 12 October 2023
Peer review completed: 19 December 2023
Received in revised form: 27 Decemb er 2024
Accepted: 4 Januar y 2024
KEYWORDS:
Biomass allocations
Decapitation
Drought stress
Multiple stress
Xylem vessel density
© 2024 The Author(s). Published by
Department of Forestry, Faculty of
Agriculture, University of Lampung.
This is an open access article under the
CC BY-NC license:
https://creativecommons.org/licenses/by-
nc/4.0/.
ABSTRACT
The interacting effects of stem decapitation, water-deficit stress, and pot
size on the growth, morpho-anatomical, and physiological traits of
Pterocarpus indicus seedlings were analyzed in this study. Changes in root
collar diameter (RCD), biomass allocation, number of leaflets (NL), mean
leaf area, guard cell size, stomatal aperture size, phloem cap fiber (PCF)
thickness, xylem vessel density (XVD), relative leaf water content (RWC),
stomatal conductance (gsw), transpiration rate (E), fluorescence quantum
yield, transpiration (E), photosynthesis (PN), and electron transport rate
(ETR) of decapitated and undecapitated P. indicus seedlings in different
pot sizes (small, medium, large) and watering regimes (every 2, 7, and 14
days) were analyzed. The decapitation × water-deficit stress × and pot size
interaction did not affect growth and morpho-anatomical variables, but
they did on most of the physiological traits. Decapitated seedlings watered
every 14 days and planted in medium or large pots have lower gsw, PN, E,
and RWC. While the RCD of large-potted and water-stressed (every 14
days) seedlings decreased, allocations to stem and fine roots increased.
Moreover, the NL and PCF significantly decreased, while the ETR and
XVD significantly increased in decapitated and water-stressed seedlings.
Overall, the decapitation-watering interaction caused significant stress to
P. indicus seedlings.
1. Introduction
Newly transplanted seedlings generally have no vast root systems; hence, they are usually
prone to transplant shock due to multiple stresses, including injury from natural disturbance (e.g.,
stem decapitation) and water-deficit stress. Previous experiments have revealed multiple stresses
that can delay the growth and survival of newly transplanted seedlings (Stoneham and Thoday
1985). However, the major causes of seedling death remain understudied. Although attempts have
also been made to increase abiotic stress resistance in transplanted seedlings, greater mortality
rates, lower shoot growth, and survival could still be observed in many plant species. Moreover,
improperly handled plants at the nursery typically do poorly if transplanted in the field (Leakey
2017). This is because seedling quality and performance are influenced mainly by the nursery
growth system and cultural practices (Haase et al. 2021). Thus, understanding how seedlings
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
114
respond to multiple stresses during the nursery phase will help us determine the desired growth
and survival level suitable to the planting site’s unfavorable environments.
Natural disturbances, such as volcanic eruptions and windstorms, are the major causes of
stem damage (decapitation or branch removal), which can influence the forest ecosystem functions
and structures by altering the growth and development of the plant (Herbert et al. 1999; Hernandez
et al. 2020; Hirsh and Marier 2002). In some studies, decapitation is a good practice for stimulating
stem growth by apical dominance (Liu et al. 2017; Pal et al. 2013). The practice of decapitation,
coppicing, or cutting of either stem or root has also been explored in several studies to increase the
number of foliage, stems, and branches (Pal et al. 2013). Decapitation-pruning interaction
displayed a high rooting capacity, and the results varied by crown and pruning intensity (Haines
et al. 1993). A simulation experiment also revealed a significant increase in xylem-specific
hydraulic conductivity following the decapitation of Betula trees (Tumajer and Treml 2019).
However, there is currently a lack of consensus and comprehensive research on how stem
decapitation and its interaction with other environmental factors function for tree species. For
example, decapitating shoots resulted in slower growth of axillary buds, and the results varied
depending on temperature (Yang et al. 2021). The re-sprouting ability of decapitated peach trees
was suppressed after applying fresh manure or organic matter (Tsipouridis and Thomidis 2003).
Contradictory findings of previous research can be ascribed to variances in species’ life-history
traits, stress intensity, and the interacting effects of multiple stresses (e.g., decapitation and water
scarcity). Moreover, the existing literature on decapitation research is focused on the impacts of
plant growth, with little information on the effects on morpho-anatomy and physiology,
particularly in tree species.
Water is the most important resource in seedling establishment and survival in the actual
planting sites, particularly during summer, in addition to excessive solar radiation and nutrient-
poor soils (Chirino et al. 2011; Jiménez et al. 2007). Seedling establishment (i.e., elongation and
emergence) is an important phase of the plant’s life cycle, as seedlings can be exposed to different
levels of water-deficit stress (Park et al. 2021), inducing transplant shock (Haase and Rose 1993).
In particular, prolonged water stress harms many aspects of plant physiology, resulting in
decreased plant growth and development, metabolic disturbance, and death (Hernandez et al. 2023;
Jaleel et al. 2008; Pallardy 2010). Unfortunately, knowledge of seedling responses to water-deficit
stress, particularly in forest tree species, is still scarce. Previous studies specifically lack emphasis
on how drought-induced changes in morpho-anatomical and physiological traits influence seedling
growth and development. Although several studies have already been done to observe the complex
physiological impacts of water-deficit stress on plants, these studies have not addressed multiple
stresses or interaction effects, such as pot size-water stress and/or decapitation-pot size-water
stress interaction effects.
Pot size significantly impacts plant growth, especially when the root environment is under
stress, through alteration in plant water use and root system morphological characteristics
(Espinoza et al. 2017; Landis et al. 1990). Previous research found that large containers led to
larger root systems, whereas small containers limit root growth and development, and these are
related to seedlings’ ability to forage water resources under water-limiting conditions (Park et al.
2021; Poorter et al. 2012; Villar-Salvador et al. 2012). The ability of the root system to forage
water in a new site is important after transplanting (Rietveld 1989). When roots are enclosed in a
container that limits their expansion, the roots become stunted, which could predispose plants to
drought stress (Ma et al. 2020). When root mass increases while rooting space is limited, there
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
115
might be intense competition for available oxygen (Balliu et al. 2021). While these pot size effects
on plant growth are well-known for many herbaceous plants, these effects are not well-documented
in forest tree species, which differ widely in functional type, growth form, water use, and root
architecture. Moreover, data on how pot size influences the response of seedlings to multiple
stresses is relatively lacking.
Pterocarpus indicus (narra) is a deciduous nitrogen-fixing tree species that grows best in
open areas. In the Philippines, it is widely used for reforestation (Gazal et al. 2004). It can be
propagated via seeds and cuttings; seedling stocks are mostly used for reforestation and
rehabilitation of denuded lands (Rise 1995). However, establishment trials in degraded forest areas
have yielded varied results, with some failing (Orwa et al. 2009). Thus, to understand how narra
seedlings respond to multiple stresses typical of denuded lands, we studied the interacting effects
of stem decapitation, water-deficit stress, and pot size on the growth, morpho-anatomy, and
physiology of narra seedlings.
2. Materials and Methods
2.1. Plant Material and Experimental Design
In March 2022, we collected P. indicus seedlings that were physically and physiologically
healthy, measuring 4.5–7.5 cm in height and 0.25–0.35 mm in diameter, from a forest floor in
Barangay Canaway, Malilipot, Albay. Seedlings were located within 5–10 m radius of large trees,
which could be mother trees. P. indicus seedlings were growing in association with other dominant
species, such as Weinmannia hutchinsonii, Astronia ferruginea, and Neoscortechinia nicobarica.
The seedlings were transported from the study site in a storage box with damp soil. Seedlings of
similar sizes were individually transplanted into pots containing a sterilized soil mixture. The
mixture, composed of coir dust, garden soil, and sand, was combined in equal parts by weight or
volume (e.g., 1,000 g), maintaining a 1:1:1 ratio. Such a soil mixture is commonly used as a potting
medium for forest tree species in the Philippines, and it effectively nurtures P. indicus seedlings.
Seedlings underwent an acclimatization period in the greenhouse, where seedlings were made to
recover in the nursery and continuously watered for two months.
After a 2-month acclimatization period, a greenhouse experiment on the interacting effects
of pot size, stem decapitation, and water stress was conducted from May to October 2022 at the
Department of Forest Biological Sciences (DFBS), College of Forestry and Natural Resources
(CFNR), University of the Philippines Los Baños (UPLB), Laguna, Philippines. The seedlings
were arranged in the greenhouse following the strip plot experimental design. Before any treatment
was applied, the development of the earliest terminal bud was monitored until the appearance of
the primordium of the first leaf based on the procedures in Chaar et al. (1997). It ensures that the
leaves/stems/roots used were only those produced during treatment. Seedlings were subjected to
three pot size treatments, i.e., small (5 × 5 × 8 cm3), medium (10 × 10 × 15 cm3), and large (15 ×
15 × 18 cm3), three watering treatments, i.e., every two days (control), every seven days, and every
fourteen days using 250 ml of tap water per seedling, and two stem decapitation treatments, i.e.,
undecapitated (control) and decapitated. We used the rounded form for the pot treatments to have
uniform root growth distribution and circulation of water and nutrients. For artificial decapitation
treatment, approximately 3 cm of apical buds of an orthotropic stem were cut from the seedlings
(N = 10). The decapitated and undecapitated seedlings were subjected to three watering regimes
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
116
across pot sizes. A total of 180 wildlings (i.e., 3 pot sizes × 3 watering regimes × 2 decapitation
treatments × 10 replicates) were used in this study. Pots were placed in the elevated seedbeds
following a 15 cm distance between seedlings and a 0.5 m distance between seedbeds. Dead and
inferior-quality seedlings were replaced during the recovery period before the treatment
application.
2.2. Growth and Morpho-Anatomical Traits Measurement
The seedlings’ root collar diameter (RCD), mean leaf area, number of leaflets (NL), and
biomass allocations were measured during the initial and final weeks of the experiment. Using a
digital caliper, the RCD of each seedling was measured. Plants were harvested after six months of
treatment application to measure biomass allocation and were separated into leaves, stems,
branches/twigs, and fine and coarse roots. The roots were gently cleansed with flowing tap water
and air-dried. The oven-drying method was then used to determine the biomass allocations at 65°C
for 48 hours.
Ten fully grown and healthy leaves attached to an orthotropic branch were randomly
collected from each pot for the measurement of morpho-anatomical traits. All leaves were taken
in the morning (i.e., 8:00 to 10:00 AM) with similar internodal orientations on twigs. Leaf samples
were packed in plastic bags and stored in a cold storage box for further analysis in the laboratory.
The mean leaf area (MLA) was determined using the grid counting method, where leaves were
traced on the 1 cm grid paper. The NL was determined by counting all leaflets in a compound leaf
of each seedling across treatments.
For anatomical analysis, young leaf and stem samples (approximately 1 mm and 2 mm) were
cut from the middle of the leaves and fixed in microcentrifuge tubes for several weeks containing
a fixative solution. The anatomical analysis was done using a freehand technique following the
procedures of Hernandez et al. (2022). Samples were dehydrated in a graded series of ethanol
solutions (50, 65, 95, and 100%) at room temperature for one month. The guard cell size, stomatal
aperture size, phloem cap fiber (PCF) thickness, and xylem vessel density (XVD) of decapitated
and undecapitated P. indicus seedlings in different pot sizes and watering regimes were determined
and analyzed in the final week. The abaxial epidermal peels were collected from each leaf using
colorless nail polish for stomatal aperture size and guard cell size measurement. Approximately
10–15 stomatal aperture and pairs of guard cells from each leaf sample were measured using digital
image processing (i.e., ImageJ). The PCF thickness (µm) and the XVD in the young stem of the
seedlings were measured using the same image processing software.
2.3. Physiological Traits Measurement
In this study, the physiology of all the seedlings, such as leaf relative water content (RWC),
stomatal conductance (gsw), transpiration rate (E), fluorescence quantum yield (ΦF), and electron
transport rate (ETR), were measured. Ten leaves were collected to determine RWC following the
procedures of Jiménez et al. (2007). Leaves were weighed to obtain the fresh mass (FM), petioles
were immersed in water overnight, reweighed to obtain turgid mass (TM), and oven-dried at 65°C
for 48 h. The RWC was then computed as (FM – DM)/(TM – DM) × 100 (Diaz-Perez et al. 1995).
The gsw, E, ΦF, and ETR were determined using a handheld LI-600 Porometer/Fluorometer (LI-
COR, Nebraska, USA). A portable photosynthesis system (LI-6400T, Li-Cor Inc., USA) was used
to measure the photosynthesis rate (PN, µmol CO2 m-2s-1). PN was measured under an artificial
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
117
irradiance of 1000 µmol m-2 s-1 with a temperature of 26°C and chamber relative humidity of 50–
70%. Measurements were done between 9:00 AM and 12:00 PM (PST) in the same healthy and
fully expanded or sun-exposed leaves (two leaves per seedling) attached to an orthotropic branch
(approximately 4–5 nodes).
2.4. Statistical Analysis
Using the “Shapiro.test”, the normal distribution of the data was initially assessed. The
effects of the treatment on the growth, morpho-anatomy, and physiology of P. indicus seedlings
were tested using a three-way ANOVA. Using Tukey’s HSD post hoc test, means were compared.
All calculations were performed using R statistical software (version R-3.5.1) at a significance
level of α = 0.05.
3. Results and Discussion
3.1. Interacting Effects of Stem Decapitation, Pot Size, and Watering Regimes on the Growth of
Pterocarpus indicus Seedlings
In Fig. 1, the RCD, MLA, and NL of both undecapitated and decapitated seedlings were, in
general, significantly lowest at 14 days water regime across pot sizes. However, there was a clear
diminishing trend in the MLA and NL values of the decapitated seedlings as the water regime and
pot size increased. The interacting effects of pot size and watering regime in decapitated seedlings
were significant only for RCD. However, the interactions among decapitation, pot size, and
watering had no significant effects on the RCD, NL, and MLA growth of both undecapitated and
decapitated P. indicus seedlings (Table 1).
Regarding biomass allocation, no significant difference was found among undecapitated
seedlings across pot sizes and watering regimes (Fig. 2). A significant difference in biomass was
observed in decapitated seedlings watered every 14 days. Specifically, stem (aboveground and fine
root (belowground) biomass significantly increases as pot size increases. The interactions of the
three variables had no significant effect on biomass allocations of undecapitated P. indicus
seedlings across all treatments (Table 1).
The results indicated that pot size-watering interaction significantly affects the plant growth
of decapitated P. indicus seedlings. A significant decrease in RCD of large-potted decapitated
seedlings watered every 14 days can be attributed to the interacting effects of the large volume of
soil and low water supply on the ability of the seedlings to absorb nutrients from the soil. This
result could explain the significant increase in fine root biomass under such conditions as they
need to forage into large pots amid a decreased water supply. Since stressed seedlings are planted
in large pots, they may have shifted the carbon allocation to increasing the belowground system to
enhance foraging traits by increasing fine root biomass instead of increasing the RCD. The increase
in fine root biomass may have improved the root surface area in contact with the soil solution and
the overall uptake of water. The main route for plants to absorb water and nutrients is through fine
roots, particularly those with a diameter of about 2 mm (Hendrick and Pregitzer 1996). An increase
in coarse roots, on the other hand, is significant in improving anchorage (Ramalingam et al. 2017;
Sorgonà et al. 2018). Hence, the observed decrease in coarse root biomass in all decapitated large-
potted narra seedlings watered every 14 days indicates a trade-off between coarse roots’ anchoring
function and fine roots’ water absorption function. Our results partially agree with those of the
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118
previous studies, i.e., plant growth of trees (Poorter et al. 2012; Salisu et al. 2018) and herbs (Al-
Menaie et al. 2012; Oagile et al. 2016) increased with increasing pot size.
Fig. 1. RCD, mean leaf area, and no. of leaflets of decapitated and undecapitated P. indicus
seedlings in different pot sizes (S, M, L) and watering regimes (every 2, 7, and 14 days) (Note:
Lowercase letters indicate statistical significance between treatments at α = 0.05 (Three-way
ANOVA)).
This tendency supports the recorded significant decrease in RWC in all decapitated potted
seedlings watered every 14 days (Table 1). This considerable drop in RWC can signal a critical
seedling water status or cellular water deficiency. In addition, the observed lower transpiration
rates (E) and stomatal conductance (gsw) may explain the potential rise in water consumption in
large-potted seedlings watered every 14 days.
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
119
We could also deduce that the increase in the belowground system is linked to a considerable
increase in stem biomass allocation of decapitated, large-potted, and water-stressed seedlings. The
observed higher xylem vessel density in decapitated, large-potted, and water-stressed seedlings
(Fig. 3) supports such a result. Increased xylem vessel or tracheid diameter and/or density
improves water transport efficiency (Hernandez and Park 2022; Pittermann 2010) and maintains
hydraulic conductance by reducing the effects of path length (Kim et al. 2014) as stem and root
length increase over time. Herrera et al. (2021) reported a contrasting pattern, i.e., xylem vessels
were larger in small pots than large ones, which resulted in a highly significant increase in the
theoretical hydraulic conductance. The difference in the results can be ascribed to many factors,
including species traits, plant organs, and treatment imposition.
Fig. 2. Biomass allocations of decapitated and undecapitated P. indicus seedlings in different pot
sizes (S, M, L) and watering regimes (every 2, 7, and 14 days) (Note: Different uppercase and
lowercase letters indicate statistical significance between treatments for total biomass
(aboveground and belowground) and plant organs, respectively (Three-way ANOVA, α = 0.05)).
3.2. Interacting Effects of Stem Decapitation, Pot Size, and Watering Regimes on Morpho-
Anatomical Traits of P. indicus Seedlings
Among the anatomical traits observed (Fig. 3–Fig. 6), the xylem density had the most
striking increase in decapitated seedlings watered every 14 days, regardless of pot sizes (Fig. 3–
Fig. 6). Guard cells and PCF thickness somehow showed a slight significant size reduction in
decapitated seedlings watered every 14 days, regardless of pot sizes (Fig. 3–Fig. 5). Surprisingly,
there was a significant increase in the stomatal aperture size in both decapitated and undecapitated
seedlings watered every 14 days, regardless of pot sizes (Fig. 3).
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
120
The interaction between decapitation and watering significantly impacted PCF thickness
(Fig. 3 to Fig. 5b) and XVD (Fig. 3 to Fig. 6b). The PCF thickness of decapitated P. indicus
seedlings watered every 14 days was significantly lower than that of undecapitated and well-
watered seedlings. A reverse pattern was observed in XVD, wherein we found no significant
interacting effects of decapitation × pot size × watering on any of the morpho-anatomical traits
studied (Table 1 and Fig. 3 to Fig. 6). However, the decapitation × pot size interaction significantly
influenced seedling guard cell size (Table 1 and Fig. 3).
Fig. 3. Guard cell size, stomatal aperture size, PCF thickness, and XVD of decapitated and
undecapitated Pterocarpus indicus seedlings in different pot sizes (S, M, and L) and watering
regimes (every 2, 7, and 14 days) (Note: Lowercase letters indicate statistical significance
between treatments at α = 0.05 (Three-way ANOVA)).
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
121
Fig. 4. Stomata of undecapitated and decapitated P. indicus seedlings in different pot sizes and
watering regimes.
The decapitation-watering interaction significantly affected the NL, PCF, ETR, and XVD
(Table 2). Although stem decapitation stimulated seedling coppicing ability as evidenced by
increased stem biomass (i.e., higher stem density per seedling), water stress may have prevented
seedlings from developing leaves to prevent excessive water loss via transpiration and carbon
consumption via photosynthesis. Water stress may have negatively affected the leaf mitotic
activity or cell division in the meristematic zone of the seedlings, ultimately influencing the
development of vegetative organs and, thus, carbon allocation to leaves. Several studies found
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
122
similar results, i.e., altered cell division due to drought stress reduced leaf growth and development
(Avramova et al. 2015; Nelissen et al. 2018).
Fig. 5. Phloem cap fibers of undecapitated and decapitated P. indicus seedlings in different pot
sizes and watering regimes.
5µm
5µm
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Fig. 6. Xylem vessels of undecapitated and decapitated Pterocarpus indicus seedlings in
different pot sizes and watering regimes.
We found a lower PCF thickness in decapitated seedlings watered every 14 days, and this
further explains the observed lower leaf production. Leaf photosynthesis is highly correlated with
CO2-diffusion capacities, controlled by leaf morpho-anatomical traits and environmental factors
(Huang et al. 2022; Ye et al. 2022; Zhang et al. 2020). Thus, a lower PCF thickness could indicate
5µm
5µm
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
124
a lower production of glucose molecules during photosynthesis, as PCF’s main role is to provide
mechanical strength to food-transporting tissues, such as the phloem. Because there was not much
glucose to transport that required mechanical support, decapitated P. indicus seedlings planted
under every 14 days watering regime may not have invested in establishing more phloem fibers
for long-distance loading. Alternatively, decapitation-water stress interaction may have negatively
affected the phloem transport mechanisms, eventually altering carbon allocation to leaves.
3.3. Interacting Effects of Stem Decapitation, Pot Size, and Watering Regimes on the Physiology
of P. indicus Seedlings
Significant interaction effects of decapitation × pot size × watering on gsw, E, PN, and ΦF
were observed in this study (Table 1). The decapitated and water-stressed seedlings planted in
medium to large pots generally had lower gsw, E, and PN compared to undecapitated and well-
watered seedlings planted in small pots (Table 2). Regarding ΦF, the undecapitated and well-
watered seedlings in small pots had a higher ΦF than other seedlings. The RWC was significantly
affected by pot size, watering, and their interaction, with well-watered and small-potted seedlings
having significantly higher RWC (Table 2). Finally, we discovered that the decapitation watering
interaction significantly affected the electron ETR. A higher ETR is commonly observed in
decapitated seedlings, particularly those subjected to watering every 14 days. This greater ETR,
however, did not result in a higher photosynthesis rate. A similar study also found that a substantial
part of PSII electron transport was not used for the photosynthesis or photorespiration of plants
exposed to different levels of drought stress (Zivcak et al. 2013).
Table 1. P-values obtained in testing the effects of stem decapitation (decapitated and
undecapitated), pot size (small, medium, and large), and watering regimes (every 2 days, every 7
days, and every 14 days) on growth, morpho-anatomical traits, and physiological traits P. indicus
using the three-way ANOVA
Variable
Decapitation
(D)
Pot size
(P)
Watering
(W)
D × P
D × W
P × W
D × P × W
GROWTH
RCD (mm)
0.880
0.843
< 0.001
0.082
0.189
< 0.001
0.177
No. of leaflets
< 0.001
0.018
< 0.001
0.221
0.003
0.082
0.101
Mean leaf area (cm2)
0.815
0.097
< 0.001
0.511
0.744
0.334
0.728
Fine roo t biomass (g)
0.231
0.002
0.984
0.199
0.003
0.420
0.163
Coarse root biomass (g)
0.127
0.558
0.115
0.577
0.141
0.501
0.463
Leaf biomass (g)
0.523
0.037
0.127
0.172
0.017
0.389
0.352
Twig biomass (g)
0.115
0.005
0.465
0.923
0.004
0.818
0.215
Stem root biomass (g)
0.076
0.794
0.061
0.583
0.030
0.548
0.915
Total biomass (g)
0.115
0.043
0.032
0.923
0.004
0.818
0.258
MORPHO-ANATOMY
Guard cell size (µm)
0.628
0.539
< 0.001
< 0.001
0.995
1.000
1.000
Stomatal aperture size (µm)
0.086
0.458
< 0.001
0.057
0.937
0.991
0.998
Phloem cap fibers thickness (µm)
0.031
0.409
0.008
0.018
< 0.001
0.999
0.999
Xylem vessel density (count seedling-1)
< 0.001
0.586
< 0.001
0.689
< 0.001
0.253
0.419
PHYSIOLOGY
Relative leaf water content (%)
< 0.001
<0.001
< 0.001
0.693
0.061
< 0.001
0.719
Stomatal condu ctance (mol H2O m−2s−1)
0.198
0.742
0.864
0.511
0.574
0.943
0.007
Transpiration rate (mmol H2O m−2s−1)
0.546
0.813
0.704
0.499
0.630
0.976
0.006
Photosynthesis (µmol CO2 m-2s-1)
0.332
0.412
0.126
0.154
0.165
0.842
0.001
Fluorescence quantum yield
0.054
0.056
0.463
0.222
0.156
0.538
0.023
Electron transport rate (µmol electrons m-2s-1)
0.001
0.035
< 0.001
0.759
< 0.001
0.683
0.809
Note: Significant effects are written in bold.
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
125
Table 2. Physiological traits of decapitated and undecapitated P. indicus seedlings in different pot sizes and watering regimes. Lowercase letters indicate
statistical significance between treatments at α = 0.05 (Three-way ANOVA)
Decapitation
Pot
size
Watering
regime
RWC
(%)
gsw
(mol H2O
m−2s−1)
E (mmol H2O
m−2s−1)
ΦF
ETR (µmol electrons
m-2 s-1)
PN
(µmolCO2m-2s-1)
Undecapitated
S
Every 2 days
88.86 (2.96)a
0.057 (0.02)a
0.84 (0.25)a
0.49 (0.15)b
7.17 (2.24)e
1.11 (2.24)a
M
89.81 (2.77)a
0.055 (0.02)a
0.72 (0.22)a
0.69 (0.02)ab
9.55 (0.43)de
0.55 (0.43)ab
L
90.09 (2.09)a
0.049 (0.01)a
0.65 (0.13)ab
0.73 (0.01)a
9.74 (0.16)de
0.44 (0.16)ab
S
Every 7 days
75.12 (1.94)ab
0.041 (0.02)a
0.63 (0.27)ab
0.64 (0.04)ab
10.05 (1.13)de
0.45 (1.13)a
M
82.05 (0.61)a
0.061 (0.01)a
0.85 (0.17)a
0.72 (0.01)a
11.39 (0.98)de
1.03 (0.98)a
L
92.16 (1.62)a
0.064(0.02)a
0.51 (0.12)ab
0.74 (0.01)a
12.59 (1.58)cde
0.89 (1.58)ab
S
Every 14
days
74.75 (1.95)ab
0.046 (0.02)ab
0.41 (0.14)b
0.72 (0.01)a
15.00 (1.30)abcd
0.90 (1.30)ab
M
71.67 (0.80)ab
0.027 (0.02)b
0.38 (0.15)b
0.67 (0.05)ab
14.81 (1.63)bcd
0.71 (1.63)ab
L
71.90 (1.17)ab
0.019 (0.02)c
1.42 (0.78)a
0.67 (0.06)ab
14.49 (1.07)bcd
0.49 (1.07)ab
Decapitated
S
Every 2 days
91.63 (1.61)a
0.023 (0.01)b
0.37 (0.16)b
0.75 (0.00)a
9.27 (0.28)de
1.27 (0.28)a
M
94.94 (1.32)a
0.031 (0.02)b
0.47 (0.17)b
0.72 (0.02)a
10.16 (0.52)de
1.26 (0.52)a
L
92.26 (2.51)a
0.043 (0.02)b
0.67 (0.28)ab
0.74 (0.00)a
10.90 (0.46)de
1.20 (0.46)a
S
Every 7 days
82.79 (1.83)a
0.047 (0.01)a
0.73 (0.19)a
0.72 (0.01)a
8.53 (0.55)de
0.83 (0.55)ab
M
88.91 (0.67)a
0.026 (0.01)b
0.46 (0.13)b
0.74 (0.02)a
9.73 (0.50)de
0.43 (0.50)ab
L
97.36 (0.55)a
0.021 (0.01)c
0.79 (0.18)b
0.71 (0.03)ab
12.89 (2.31)cde
0.19 (2.31)c
S
Every 14
days
38.42 (2.68)b
0.014 (0.01)c
1.02 (0.13)a
0.64 (0.01)ab
19.45 (1.74)abc
0.45 (1.74)ab
M
39.04 (1.05)b
0.017 (0.01)c
0.92 (0.20)a
0.72 (0.01)a
22.11 (2.22)a
0.15 (2.22)c
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
126
The results can be attributed to several factors, such as leaf temperature, light, phloem
transport mechanisms, enzymes, CO2, and leaf anatomical structures. For example, water stress
significantly inhibited the linear electron transport in leaves depending on leaf temperature,
although residual electron transport was higher in water-stressed leaves than in control (Loreto and
Marco 1995). The ETR in decapitated and water-stressed P. indicus seedlings may be higher.
However, the leaf exterior and interior environments may not have been suitable for establishing
a proton gradient for ATP and NADPH production to complete the photosynthetic process. During
the experimental period, water stress-induced modifications in the photosynthetic reaction centers
could have also occurred (Zong et al. 2014), influencing the plant leaf’s photosynthetic machinery.
This tendency can be seen from the observed lower gsw, which leaf morpho-anatomical traits can
influence in decapitated and water-stressed seedlings. Generally, a decrease in gsw results in
photosynthesis limitation (Noormets et al. 2001).
While the interactions between decapitation, pot size, and watering did not affect growth and
morpho-anatomical variables, the decapitated and water-stressed seedlings grown in medium
and/or large pots exhibited lower gsw, PN, E, and RWC than other seedlings. This result implies
that interacting multiple abiotic stresses can negatively trigger the complex physiological
responses in P. indicus seedlings. Although either decapitation or water stress inhibited seedling
development, results imply that large-potted seedlings’ survival may be improved when exposed
to abiotic stresses by lowering gsw, PN, and E while retaining high ETR. Rising CO2 concentrations,
which may have resulted from high ETR in leaves, can cause a decrease in stomatal conductance,
resulting in a decreased rate of transpiration and improved plant water use efficiency (Ainsworth
and Rogers 2007). Moreover, the high ETR can be attributed to the observed high stomatal aperture
size in decapitated and water-stressed seedlings in medium and large pots. Such a high ETR may
have provided sufficient ATP to fuel ion exchanges during the stomatal opening for
osmoregulation or stomatal aperture regulation and photosynthesis via chloroplast-containing
guard cells (Lawson 2008; Shimazaki and Zeiger 1985). Thus, CO2 levels may have been fully
used up by photosynthesis that possibly took place in the guard cells, triggering the opening of the
stomatal aperture of P. indicus seedlings for replenishment.
4. Conclusions
Through a greenhouse experiment, we investigated the interacting effects of decapitation,
pot size, and water stress on the growth, morpho-anatomy, and physiology of P. indicus seedlings.
While the interactions of the three factors had no significant impact on growth and morpho-
anatomical traits, they did on most physiological traits of the seedlings. Medium and large-potted,
decapitated, and water-stressed seedlings had lower gsw, E, PN, and RWC and higher ETR than
those in control. We also detected a significant effect of pot size-watering interaction on plant
growth (i.e., RCD, biomass allocation, particularly to stem, fine root, and coarse root) of
decapitated P. indicus seedlings and decapitation-water stress interaction on some of the morpho-
anatomical and physiological traits (i.e., no. of leaflets, PCF, XVD, and ETR). Overall, we found
that the response on growth, morpho-anatomy, and physiology of P. indicus seedlings to multiple
stresses (decapitation and water-deficit stress) can be improved by planting the seedlings in
medium and/or large pots during initial growth in the nursery. Although the responses might differ
in the field, planting the seedlings in medium or large containers could be a potential nursery
practice for improving the survival of the seedlings against multiple abiotic stresses. However,
Hernandez et al. (2024) Jurnal Sylva Lestari 12(1): 113-131
127
large-scale field experiments are recommended to elucidate the responses of the seedlings,
particularly the newly transplanted ones, to multiple stresses.
Acknowledgments
This study is supported by the University of the Philippines Los Baños-funded Basic
Research, Philippines.
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