Effects of different water levels, light intensities and durations of shading on growth and development of young Tongkat Ali (Eurycoma longifolia Jack)
In this study, the effect of different levels of irrigation water, light intensities and durations of shading on growth and development of young Tongkat Ali (TA; Eurycoma longifolia Jack) was considered. Large cultivation of TA is still very lacking due to i...
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| Format: | Thesis |
| Language: | English |
| Published: |
2019
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/84051/1/FP%202019%2054-ir.pdf |
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| Summary: | In this study, the effect of different levels of irrigation water, light intensities
and
durations of shading on growth and development of young Tongkat Ali (TA; Eurycoma
longifolia Jack) was considered. Large cultivation of TA is still very lacking due to
insufficient and inconclusive information of its agronomic cultivation requirements; thus, over
collecting from the tropical rain forests for commercial production of traditional medicines
will ultimately endanger and lead to the species extinction. In order to sustain the
continuous supply of plants raw material for industrial production, there is an urgent
need to determine the essential growing requirements of this plant for the establishment of
plantations of TA, particularly, in the nursery. Hence, three experiments were conducted to
examine the agronomic requirements: Water levels, light intensity and shading duration of young
TA. The first experiment was laid down out a Randomized Complete Block Design (RCBD) with five
watering regimes imposed onto 6-month old TA seedlings from Hulu Langat, Selangor,
Malaysia, namely at 125%, 100%, 75%, 50% and 25% of field capacity (FC), placed in six
blocks. The main objective of the study was to evaluate the effect of different levels of
irrigation water on growth and development of TA, especially the root growth and its
relationship with the shoot growth. There were obvious differences among young TA seedlings
for sensitivity to water stress due to the different levels imposed. Growth parameters also
decreased with increasing severity of water scarcity, although by the end of the
experiment, they were not significantly different under treatment 75% FC compared to
non-water stress, especially in total biomass and total leaf area. Root parameters,
especially root length, root diameter, root volume and specific root length (SRL) by
end of the experiment demonstrated noticeable differences among young TA seedlings treated with
different water levels. In the second experiment with the main objective to determine
plant responses to the interaction between water availability and various light intensities on
growth and development of TA, especially the root growth, the combined treatments were arranged
using RCBD with a split plot layout consisting of 2 factors of three different light intensities
(no cover, 50% shading, 70% shading) and three different water treatments (100% FC, 75% FC, 25% FC) blocked three
times. Results showed that plant growth parameters including plant height, stem diameter
and total biomass were reduced only by light scarcity condition and root/ shoot ratio; meanwhile,
height ratio was higher in 70% shading compared to 50% shading and the control
conditions. After 4.5 months of combined light and water treatments, seedlings exposed
to 50% shading combined with 75% FC (moderate water stress) recorded the highest values
for total plant leaf area (TLA; 331cm²), specific leaf area (SLA; 134 cm²/g), chlorophyll
concentration (CHL; 42.6 µmol/m²) and nitrogen balance index (NBI; 22.1) compared to 70%
shading imposed with water stress at 25%FC showing lower values for TLA (16.7 cm²), SLA (31.7
cm²/g), CHL (17.3 µmol/m²) respectively. Likewise, there were
parallel decreasing trend in root parameters (root length, root diameter, root volume and
SRL) with non-shaded plants resulting in fine root with decreased root density, which
severity escalated (decreased by 46%) with decreasing light intensity at 70% shading compared
to non-shaded condition. The second experiment clearly demonstrated the effect of light
sensitivity of young TA seedlings, especially on root density, and this sensitivity became severe
when plants were further imposed with water deficit. The third experiment investigated plant
light requirement based on the duration of 50% shading imposed for 45, 30 and 15 days after start
of treatment and combined with three different water treatments (100% FC, 75% FC, 25%
FC). Treatments were laid out in a split plot arrangement based on RCBD with three
blocks with the objective to investigate the effect of different duration of 50%
shading on root system, and the morphological and physiological traits of TA. Results
from the experiment showed that there were recognizable differences among young TA seedlings
exposed to shading duration and water treatments. The decrease in shading duration from 45 to 15
days seemed to have increased both the peroxidase (POX) and malondialdehyde (MDA) in both root and
shoot parts compared with 30 days shade duration treatment. Similarly, plants imposed with
45 and 15 days shading also recorded decrease in plant height (4%~8%), shoot diameter (2%~8%),
root length (2%~8%) and root diameter (15%~20%) compared with 30 days of shading
duration. The root also seemed to be more sensitive than the shoot to both POX and MDA under either
too short (15 d) or too long shading duration (45 d). In the present study, the role of peroxidase in the growth of TA seedlings was examined
by relating plant height, stem diameter and root parameters, in particular root length and root
diameter, with peroxidase activity, which indicated that reduction in peroxidase activity
was associated with the tallness and thickness of the plant, which correlated with root length and
root diameter with significant correlation, such that,
30 days shading duration exhibited highest value in shoot and root parameters compared
with other shade durations. Conversely, plants exposed to short duration of shading treatment (15
d longer exposure to sunlight) exhibited greater values of MDA and POX than those exposed
to 45 d shading duration with 1.2% increase in MDA in both root and shoot, and in case of POX with
33% increase in root and 20% increase in shoot, respectively. In a nutshell, even though
long time shading has negative effects on growth and development, short time shading
duration led to excess light intensity and has more detrimental effects. In conclusion, by
evaluating the effects of different levels of irrigation water, various light intensities and
different durations of shading on root and shoot traits, morphologically, physiologically and
biochemically, the 50% shading at 30 d duration combined with water at 75% FC seemed to
give the optimum growth and development condition for establishment of
TA seedlings. |
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