Vascular Bundle Distribution Effect on Density and Mechanical Properties of Oil Palm Trunk
Dodik Ridho Nurrochmat,
Muh. Yusram Massijaya,
Eka Mulya Alamsyah,
Effendi Tri Bahtiar
Palm oil tree (Elaeis guineensis Jacq.) is a plant
species which belong to monocotyledons. The Oil Palm Trunk (OPT) is composed
of vascular bundles and parenchyma as ground tissue which determine the properties
of the wood. This study was conducted to find out the effect of the vascular
bundles toward the density and mechanical properties of OPT in vertical and
horizontal direction. The results showed that in horizontal position (outer
to the center zone of OPT), the greater number of the vascular bundles contained
in trunk made the density value and the mechanical properties greater but in
vertical position showed otherwise. The number of vascular bundles is not the
only factor that determines the density and mechanical properties of OPT. The
top section of OPT has a lower density and mechanical properties than the bottom
even though the number of vascular bundles can be greater. This happens because
the vascular bundles in the top are composed by the younger cells than the bottom.
to cite this article:
Atmawi Darwis, Dodik Ridho Nurrochmat, Muh. Yusram Massijaya, Naresworo Nugroho, Eka Mulya Alamsyah, Effendi Tri Bahtiar and Rahmat Safe`i, 2013. Vascular Bundle Distribution Effect on Density and Mechanical Properties of Oil Palm Trunk. Asian Journal of Plant Sciences, 12: 208-213.
Received: December 03, 2013;
Accepted: January 15, 2014;
Published: March 18, 2014
Palm oil tree (Elaeis guineensis Jacq.) is a plant species which belong
to monocotyledons. Oil Palm Trunk (OPT) is a non-wood lignosellulosic material
(Hashim et al., 2011) and its anatomical structure
is different with wood in general (Tomimura, 1992).
The main components of OPT are vascular bundles and parenchyma tissue. Both
components are essential to the basic properties (Tomnilson,
1961). Vascular bundles in the OPT are not evenly spread but concentrated
on the outer and spread toward the center zone of the OPT (Tomnilson,
1961). Based on the depth of the OPT (horizontal), the number of vascular
bundles decreases towards the inner of the trunk (Shirley,
2002; Erwinsyah, 2008) while from the bottom to the
top of the OPT (vertical) it tends to increase in number (Lim
and Khoo, 1986). The number of vascular bundles is the closest relative
parameter to the density and mechanical properties of the OPT, especially in
the depth direction of the trunk. The density and mechanical properties of the
OPT tend to increase within increasing number of vascular bundles (Khoo
et al., 1991; Prayitno, 1995; Bakar
et al., 1998, 1999; Balfas,
2006; Ratanawilai et al., 2006; Erwinsyah,
2008; Iswanto et al., 2010). However, this
conclusion is obtained based on the analysis of the depth direction only on
each specific height. Lim and Khoo (1986) reported that
the number of vascular bundles increased from the bottom to the top of the OPT
but the density and mechanical properties were decreasing. Cells making up the
vascular bundles at the top of the OPT are still young age than those at lower
levels and the growth is still influenced by the apical meristems. Young cells
would have different properties than mature cells. Therefore, besides influenced
by the number of vascular bundles, density and mechanical properties the OPT
are influenced by the height of the trunk also. The top of the OPT may have
a proportion of vascular bundles more than the bottom, however, because the
vascular bundles are composed by young cells, the density and mechanical properties
of the OPT at top section may be lower than the bottom. This study has more
details in observations.
MATERIALS AND METHODS
The OPT used in this study were harvested from PTPN 7 Lampung, Indonesia. Altogether,
two OPT of 20 year-old palms were harvested. Samples used were derived from
a variety of depth or heights level of the OPT. The samples were taken from
2 m (bottom), 4 m (middle) and 6 m (top) from the base of the OPT.
||(a) Test sampling distribution of vascular bundles, density
and mechanical properties at various heights level of oil palm trunk and
(b) Sampling distribution of the vascular bundles of physical mechanical
properties of the outer to the center of the OPT
Based on the depth from outer to the center zone of the OPT with 2.5 cm distance
multiples, observation samples from each height were sorted. The samples to
calculate the distribution of vascular bundle are in the disk form with a thickness
of 5 cm (Fig. 1). The sample size and testing standard of
density and mechanical properties refer to British Standard 373: BSI,
1957. Prior to testing, all samples were conditioned in the condition chamber
to attain Moisture Content (MC)±14%. The total of sample test is 48 per
parameter wood properties. Testing of mechanical properties is using a Universal
Testing Machine (UTM) Instron model 330.
The distribution of vascular bundles is defined as calculation of the number
of vascular bundles per unit area (cm2). Calculations are using a
magnifying glass (10 times). Extensive observations are in the form of an equilateral
tetrahedron (2x2 cm). Observations start from the outers toward the center zone
at various heights level. The results of the research data were analyzed by
regression analysis to find the relationship between the distribution of vascular
bundles cm-2 and the density and mechanical properties of the OPT.
This statistical data processing is using Microsoft Excel 2007 software.
RESULTS AND DISCUSSION
The OPT is an organic material composed of diverse cells that are fiber, vessel
or metaxylem, protoxylem, protophloem or sieve tubes, axial parenchyma, stegmata
and companion cells (Tomnilson, 1961; Lim
and Fujii, 1997). Those cell components are a constituent of the vascular
bundles. Vascular bundles are anantomical component which played the most important
role on the properties of the OPT. The distribution of vascular bundles has
many variations in the OPT. The number of vascular bundles decreases from the
center to the outer zone of the OPT and from the top to the bottom of the OPT.
The number of vascular bundles is negatively correlated with distance of the
test sample from the outer to the center, on the contrary it is positively correlated
with the height of test sampling (Table 1).
Density and mechanical properties of the OPT declined from the outer to the
center (Fig. 2) but based on trunk height level, density and
mechanical properties increased from the top to the bottom (Fig.
3). Being outer toward the center zone caused extensive number of vascular
|| Correlation between vascular bundles with horizontal and
vertical position on OPT
|| Average density and mechanical properties and the No. of
vascular bundles: Outer to the center of the OPT
||Average density and mechanical properties and the No. of vascular
bundles in the Bottom (2 m), middle (4 m) and top (6 m)
The vascular bundles contributes reviewed in a horizontal position, the number
of vascular bundles was positively correlated with the density and mechanical
properties. However it was negatively correlated when viewed in the vertical
According to Lim and Khoo (1986) differences in density
and mechanical properties of the OPT from the to density and mechanical properties
of the OPT so as the greater number of the vascular bundles, the OPT properties
is increasing as well. One of component constituent cells of vascular bundles
is fiber cells. At the outer zone of the OPT, the fiber is shorter than the
inside but has a smaller diameter and thicker cell walls. These thick wall fibers
shows higher cellulose content and make the material becomes stronger (Shirley,
2002). He further reported that the number of cell wall layers decreases
from the outer to the center zone and from the bottom to the top of the OPT.
More proportion of vascular bundles on the outer than the center zone proves
less proportion of parenchymal tissue at the outer than the center zone. Parenchyma
is a living tissue that functions physiologically as a store of food reserves.
Fiber, protoxylem, metaxylem and phloem coalesce into vascular bundles, a network
that serves as reinforcing and transport systems in the OPT. A large proportion
of parenchyma on the center zone of the OPT shows that the center zone of the
OPT has a dominant function as a store of food rather than a structural function.
This causes the density and mechanical properties of outer zone of OPT are higher
than the center zone. Smaller proportion of parenchyma on the outer of the OPT
serves as a reinforcement trunk more than its physiological function so that
the outer of the OPT is always more powerful than the center zone. Based on
their chemical composition, α-cellulose content of the vascular bundles
is greater than in the parenchymal tissue 42.51 and 9.03%, respectively (Abe
et al., 2013). The more the proportion of vascular bundles in the
OPT, the higher the α-cellulose contains. This makes the outer zone of
the OPT has a density and higher mechanical properties compared to the center
zone High density OPT is always more powerful than low density. There is a close
correlation between the densities with the strength of the OPT. The composition
of such a unique cell (the outside is more powerful than the inside) is an example
of a natural setting that gives the maximum moment of inertia of the OPT to
prevent bending and deflection of symptoms so that the OPT is stronger to withstand
the load during his lifetime.
In contrast to the vertical direction despite the increased number of vascular
bundles from the bottom to the top, the density and mechanical properties were
decrease. According to Lim and Khoo (1986) this happens
because of the age of the vascular bundles at the top are younger than the bottom.
During its growth the cells in the top portion of the trunk is influenced by
the apical meristems so it has not perfectly differentiated. The younger cells
tend to be soft and have low density compared to older cells due to incomplete
lignification process. Lignin is a natural polymer that combines the power and
flexibility of cellulose in the cell wall. Lignin also fills the space between
the middle lamella so that the OPT become tougher. Lignin binds to cells so
that the fibers can work together simultaneously during weight-bearing. The
perfectly lignification cells have better mechanical physical properties than
the young. Density of vascular bundles decreases from the bottom to the top
of the OPT (Rahayu, 2001). The number of cell wall layers
of fibers increases from the bottom to the top of the OPT. The thicker the cell
wall, cellulose content is also increasing so that the strength of the material
is also higher (Shirley, 2002). Fiber cells are the largest
components of the vascular bundles than the others so they greatly affect their
A model with a dummy variable is then tried to estimate the effect of the number
of vascular bundles at different heights level on the density and mechanical
properties of the OPT. The model built is:
||Density or mechanical properties (MOE, MOR, compression parallel
to grain, hardness and shear parallel to grain)
||No. of vascular bundles
|z1 and z2
||Binary dummy variables (binary dummy variables) that represents the height
of the OPT origin sample
|b, c, d
The model is able to explain most of the variation in the density and mechanical
properties of the OPT with a coefficient of determination (R2) of
82 -89% (Table 2). As shown in Table 2,
both measured variables (number of vascular bundles and sample height position
origin) show significant effect on the density and mechanical properties (MOE,
MOR, compression parallel to grain, hardness and shear parallel to grain) of
||Effect of No. of vascular bundles of the (a) Density and mechanical
properties of wood at a heigh level of 2, 4 and 6 m of the OPT, (b) Modulus
of elasticity, (c) MOR, (d) Compression/to grain, (e) Hardrness and (f)
In general, the greater number of vascular bundles contained in the OPT, the
density and mechanical properties were increase (Fig. 4).
Besides being influenced by the number of vascular bundles, density and mechanical
properties of the OPT are also influenced by the location of the origin of the
OPT height sampling tests. As shown in Fig. 4, curve number
of vascular bundles with density and mechanical properties of the OPT to the
top is always under the base curve. Top section of the OPT has a lower density
and mechanical properties than the bottom even though the number of vascular
bundles can be greater.
||Summary of regression coefficient and p-value relationship
between the No. of vascular bundles (x) at various heights (z1, z2) with
the density and mechanical properties of OPT
The density and mechanical properties of OPT is affected by the number of vascular bundles. The greater number of vascular bundles makes the density and mechanical properties better. But the number of vascular bundles is not the only factor that determines the density and mechanical properties of OPT. The top section of the OPT has a lower density and mechanical properties than the bottom, even though the number of vascular bundles can be greater. This happens because the vascular bundles of top section are composed by the young cells while the bottom section are composed by mature cells.
We wish to thank PTPN 7 Lampung which has provided the raw material for this study and this research was sponsored by MP3EI Research Skim, Directorate General of Higher Education, Ministry of Education and Culture Republic of Indonesia.
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