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American Journal of Plant Sciences, 2021, 12, 926-933
https://www.scirp.org/journal/ajps
ISSN Online: 2158-2750
ISSN Print: 2158-2742
DOI:
10.4236/ajps.2021.126062 Jun. 23, 2021 926 American Journal of Plant Sciences
Macroplastics on Soil-Plant System: Inhibiting
Effects of Macroplastics on the Growth of
Green Amaranth (Amaranthus viridis)
Marzan Ferdous, Arifur Rahman Bhuiyan*, Khadiza Akter Tania
Department of Environmental Science, Faculty of Science and Technology, Bangladesh University of Professionals,
Mirpur Cantonment, Dhaka, Bangladesh
Abstract
In recent time Bangladesh faces a serious problem of soil pollution due to
plastic contamination. However, the degree of the extent to which
the effects
of plastics on plant growth occur is not properly identified. An experiment
was conducted to measure the effects of mixed plastic (polyethylene and dis-
posable plastic glass) on the growth of
Amaranthus
viridis
. Different doses of
mixed plastics (T0, T1, T2, and T3) were applied with a fixed amount of soil
for each of the treatments e.g., T0 (control), T1 (10 gm mixed plastics/3kg
soil), T2 (15 gm mixed plastics/3kg soil) and T3 (20 gm mixed plastic/3kg
soil), and the growth response of
Amaranthus
viridis
against plastic was ob-
served for six consecutive weeks. The growth was measured in terms of plant
height and girth diameter. The results showed that the presence of mixed
plastic had a significant effect on the growth of
Amaranthus
viridis
and par-
ticularly in treatment T3 (3 kg soil/20gm mixed plastic), the plants showed a
slower growth response compared to control and the rest of the treatments
applied in case of both plant height as well as girth diameter. The statistical
analysis (one-way Analysis of Variance) also proved the
significance of the
treatments (p-
values < 0.05) for six consecutive weeks. The experiment was
successfully able to set an index on which plastics had their effects on the
growth of green amaranth. In addition, the obtaine
d data will be helpful in
future research of the study in determining the possible effects of plastic on
plant growth viz. green amaranth.
Keywords
Green Amaranth, Soil Pollution, Polyethylene Contamination, Disposable
Plastic, Abiotic Stress, Slow Growth of Plants
How to cite this paper:
Ferdous, M.,
Bhuiy
an, A.R. and Tania, K.A. (2021) Ma-
cropl
astics on Soil-Plant System: Inhibit-
in
g Effects of Macroplastics on
the Growth
o
f Green Amaranth (
Amaranthus
viridis
)
.
American Journal of Plant Sciences
,
12,
926
-933.
https://doi.org/10.4236/ajps.2021.126062
Received:
May 10, 2021
Accepted:
June 20, 2021
Published:
June 23, 2021
Copyright © 20
21 by author(s) and
Scientific
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access
M. Ferdous et al.
DOI:
10.4236/ajps.2021.126062 927 American Journal of Plant Sciences
1. Introduction
Plastic is a synthetic polymer and without it, modern life would be impossible.
Due to a wide spectrum of positive characteristics such as light, flexibility, non-
rusting, and highly persistent, plastic products hold a very important role in our
daily activities [1]. A tiny part of plastic used all over the world is being recycled
or incinerated in waste-to-energy facilities. Bangladesh is reportedly 10th in
plastic waste disposal in the world [2]. Every year 800,000 tons of waste are gen-
erated in Bangladesh, out of which 200,000 tons are from plastics [3]. However,
the chemical bond of the monomers responsible for the durability of plastic
makes it resistant to the different natural processes of degradation. The plastic
waste does not decompose, rather they accumulate on landfill and marine envi-
ronment [4]. Once in the soil, plastics can be further degraded into small par-
ticles via physical, chemical, and biological processes [5].
Additionally, the presence of plastic affects soil fertility in several ways. Plas-
tics might alter the physico-chemical properties of soil by changing its texture
and structure due to the distinctive characteristics of plastics compared with
natural soil components [6]. When soil is contaminated with plastics, its pore
structure, bulk density, and water holding capacity can be altered [7]; as a result,
soil water evaporation and shrinkage cracking may also be affected. The compo-
sition and diversity of microbial communities in soils play an important role in
maintaining soil quality [8] [9]. Microbes are sensitive to soil contaminants, and
their composition and activity are the primary biological indicators of changes in
the soil environment, as they play a key role in carbon, nitrogen, phosphorus,
and potassium cycling in the soil [10] [11].
Soil enzymes with a high capacity for catalysis are closely associated with mul-
tiple soil biochemical processes; these enzymes act as an indicator for evaluating
soil fertility and play an essential role in the regulation of soil nutrient cycling
for nutrients such as C, N, and P [12] [13]. The soil system is the chief source for
agriculture [14]. So maintained good soil conditions is mandatory to meet our
present and future food demand. Some research already proves that Plastic waste
remaining in a wide area of the soil are accumulating over a long period, causing
the soil to harden and affects the crop’s absorption of nutrients and water con-
sequently. It leads to a reduction in crop outputs [15]. One Research also esti-
mated the negative impacts of plastic bags on agriculture, e.g., reduction in soil
fertility, decrease in nitrogen fixation, huge loss of nutrients in the soil, decrease
in crop harvest, the disparity in flora, and fauna on soil, etc [16].
The present study examined the effects of mixed plastic on the growth of
Green amaranth plants. The result of the study might help the researchers in a
future study to identify the effects of plastic on plant growth and determine the
threshold limit of plastics in soil against which plants can be able to grow.
2. Materials and Methods
2.1. Experimental Procedure
The experiment was carried out from August to December 2020. A Completely
M. Ferdous et al.
DOI:
10.4236/ajps.2021.126062 928 American Journal of Plant Sciences
Randomized Design (CRD) was followed. The experimental procedure involved
three steps:
2.1.1) Plant Preparation;
2.2.2) Soil Preparation;
2.2.3) Set up of the Experimental Pots.
2.1.1. Plant Preparation
Green amaranth was selected for this study which is a cosmopolitan species in
the botanical family
Amaranthaceae
[17]. The reason for choosing green ama-
ranth was, it is fast growing and the responses could be observed within the
shortest period. It is an annual herb with an upright, light green stem that grows
to about 60 - 80 cm in height. It has several nutritional values such as it can con-
tain up to 38% protein by dry weight. The leaves and seeds contain lysine, an
essential amino acid [18]. Seeds of green amaranth were collected from the seed
market at Tongi, Gazipur, Dhaka, Bangladesh in July 2020. Seed viability test
was carried out before planting by floatation method. The seeds were sown at
first in the seedbed and allowed to grow until they were about 3.40 - 3.45 cm tall
before transferring them into the treatment pots.
2.1.2. Soil Preparation
The experimental soil was silty loam, which was collected from a local nursery at
Tongi, Dhaka, Bangladesh. After the soil was air dried, it was grounded with
mortar and pestle and passed through a sieve and the pH was measured by using
a pH meter.
Two types of plastic were used in this experiment: 1) polyethylene bag and 2)
disposable plastic glass. For the experiment, both types of plastics were cut into
pieces using scissors to reduce the plastic size. 10 grams, 15 grams, 20 grams of
mixed plastics granule was prepared for three treatments and the ratio of one-
time plastic glass and polyethylene was 1:2.3.
2.1.3. Setup of Experimental Pots
The experiment consisted of four (4) treatments each with three replications as
follows:
T0 = control (untreated 3 kg soil);
T1 = 0.33% treatment level (10 gm shredded mixed plastic/3kg soil);
T2 = 0.5% treatment level (15 gm of shredded mixed plastic/3kg soil);
T3 = 0.66% treatment level (20 gm of shredded mixed plastic/3kg soil).
Healthy and stable seedlings with a height of approximately 3.40 - 3.45 cm
were uprooted from the seedbed and four seedlings were transplanted in each
treatment pot. All the pots were exposed to natural sunlight conditions and care
was taken to keep the plants free from weed or insect infestation. The plant
height was observed for six consecutive weeks and was measured from the soil
surface to the apical tip just after plantation. Plant steam diameters were meas-
ured in the 2nd week, 4th week, and 6th week of the plantation.
M. Ferdous et al.
DOI:
10.4236/ajps.2021.126062 929 American Journal of Plant Sciences
2.2. Data Analysis
All data were statistically analyzed by using Microsoft Excel (version 2010).
One-way ANOVA (Analysis of Variance) was conducted to establish significant
differences among the treatments at a 5% level of significance using Microsoft
Excel (version 2010).
3. Results
3.1. Observation on Plant Height
Measured average heights of
Amaranthus
viridis
against different treatments were
plotted against the number of observations (in weeks) and shown (Figure 1).
At 0-week height of all treatment plants were approximately the same size
(3.42 - 3.45 cm). At 1st week after planting, the plant’s growth response of all the
treatments was observed where all the treatments showed similar height except
T3 (5.36 cm). This difference in treatment T3 has been distinctly observed after
the 2nd week, followed by the 3rd week, and continued up to the 6th week. On six
weeks of observation, plants showed the slowest growth response in treatment
T3. On the other hand, treatment T0 continued to show a significant response
with the increase of plant height. Treatment T1, T2, and T3 showed a gradual
decrease in the growth of plants (Figure 1).
After 3rd week, a noticeable reduction of growth was observed in treatment T2
and T3 (Figure 1). In 4th week, the value of treatment T0 was 20.98 cm. Howev-
er, the growth of plants in case of other treatments were 17.15 cm (T1), 15.15 cm
(T2), 12.4 cm (T3) (Figure 1).
After the 5th and 6th week, the highest growth response was observed in T0 and
the lowest was found in treatment T3. However, moderate growth was observed
in treatment T1 and T2 (Figure 1). At 5th Week the height of treatment T0, T1,
and T2 was respectively 34.48 cm, 28.5 cm, 20.51 cm, 17.74 cm and for 6th week
40.05 cm (T0), 35.52 cm (T1), 24.84 cm (T2), 19.6 cm (T3). So, it was clearly
observed that T3 had the slowest growth response compared to the control T0,
whereas treatment T1 and T2 had moderate growth response.
Figure 1. Average height (cm) of
Amaranthus
viridis
in six consecutive weeks.
M. Ferdous et al.
DOI:
10.4236/ajps.2021.126062 930 American Journal of Plant Sciences
The similar result was found from some other researchers’ experiment [19]
[20]. They [19] conducted a study with five treatments in eight weeks. Among
them, one treatment served as a control and the other contained several doses of
polyethylene. They also identified significant height reduction of maize plants in
the presence of polyethylene granules and observed the lowest growth rate in the
highest doses of treatment. Another researcher also revealed that the presence of
both macro-and micro-plastic residues of polyethylene mulch films has negative
effects on both above-ground and below-ground parts of wheat [20].
3.2. Observation on Steam Girth Diameter
Figure 2 clearly indicates that, plants of treatment T0 had the widest diameter
value (0.9 cm) while treatment T3 had the least stem girth diameter value (0.56
cm) detected at the 6th week of observation after the plantation. They [19] also
found a similar result in their experiment 8 weeks after planting. They detected
the reduction of girth diameter of
Zea
mays
while several doses of polyethylene
were applied.
4. Discussion
The results obtained from Sections 3.1 and 3.2, show that the growth (consider-
ing both height and girth diameter) of
Amaranthus
viridis
was highest in the
absence of mixed plastic in soil (T0). Whereas the presence of mixed plastics in
treatment T1, T2, and T3 showed a reduction of growth rate in
Amaranthus
vi-
ridis
(Figure 1 and Figure 2). Additionally, it had been observed that the higher
the doses of plastics in treatment, the slower the growth rate e.g., the amount of
mixed plastic was highest in treatment T3, and it showed the lowest growth rates
of
Amaranthus
viridis
. Hence the significant effect of mixed plastic on growth
was clearly visualized with a gradual increase with time. For example, after 3rd
week the growth reduction was more easily detected (Figure 1 and Figure 2).
On the 4th, 5th, and 6th week, treatment T2 and T3 showed significantly slower
growth response compared to other weeks (Figure 1). Girth diameter also
reduced with time in the case of various treatments particularly in T3 (Figure 2).
Figure 2. Average girth diameter of
Amaranthus
viridis
observed at 2nd, 4th, and 6th week.
M. Ferdous et al.
DOI:
10.4236/ajps.2021.126062 931 American Journal of Plant Sciences
The reasons behind this might be, with the increasing time plants need to up-
take more nutrients for their growth. But the shredded plastic obstructs the free
movement of root hair. Additionally, soil pore spaces also block by shredded
plastics that contain adequate air and water. As a result,
Amaranthus
viridis
root
could not uptake sufficient water and nutrient for their growth. However, plant
respiration was also hampered due to a lack of well-aerated conditions in the
soil. As the presence of shredded mixed plastic disturbed soil natural condition,
Amaranthus
viridis
growth was also affected.
Statistical Analysis
One-way ANOVA was done to determine the significance of the treatments
applied at a 5% level of confidence using Excel. ANOVA test also showed that,
Amaranthus
viridis
height at the first week of observation, the p-value was
0.001185 which was less than 0.05 and it indicates that, there had been signifi-
cant differences in the treatments. Additionally, the p-value of week 2, week 3,
week 4, week 5, and week 6 were respectively 1.8 × 10−6, 7.61 × 10−11, 1.95 × 10−14,
4.07 × 10−24, 6.08 × 10−26 and all the values were less than 0.05 for between and
within the groups. It was also observed that after the 2nd week the p-value was
drastically reduced.
Similar results were also found in the case of steam girth diameter. The
p-value of ANOVA test found for week 2, week 4, and week 6 was respectively
1.47 × 10−9, 1.35 × 10−5, 2.69 × 10−10 and all the values were less than 0.05 for be-
tween and within groups which clearly indicate that there had been significant
differences in the treatments applied to observe the plants growth. So, the statis-
tics proved the significant differences between and within the groups (within
treatments).
5. Conclusion
The study suggests that the presence of macroplastics in soil had significant ef-
fects on plant growth. The results also proved that there is a certain withstand
point beyond which the plants will collapse to show any growth progress further.
Thus, these indexing or threshold values could be helpful in future research and
will provide valuable data regarding plant’s tolerance limit against plastic con-
tamination in soil.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this
paper.
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