THREAT OF DOMESTIC POWER GENERATORS TO TERRESTRIAL
ECOSYSTEM AS EXPRESSED IN SOME PLANT SPECIES.
J. E. Otoide1 and J. Kayode2
Department of Plant Science, Ekiti State University, P.M.B 5363, Ado-Ekiti, Nigeria,
1
E-mail: joeotoidejo@yahoo.com, 2E-mail: jokayode@ymail.com
Polluted populations of Euphorbia heterophylla, Chromolaena odorata Commelina
diffusa and Kyllinga pumila were collected fresh from within 0.1-0.25m radii of the
exhausted-pipe of power generators used for domestic purposes while their non-polluted
counterparts were collected from distances of 100-110m away. The length and width of
ten leaves, each of both polluted and non-polluted populations, were measured. Their
average leaf areas (LA) were 2.60 + 0.1cm2, 14.16 + 0.4cm2, 5.19 + 0.8cm2 and 1.80 +
0.8 cm2 for the polluted populations of each of the species respectively while the average
leaf areas (LA) of their non polluted counterparts were 4.18 + 0.7 cm2, 34.39 + 0.2cm2,
7.51 + 0.1cm2 and 10.76 + 0.3cm2 respectively. Damages such as plugged stomatal pores,
epidermal cell aberrations and erosion, ruptured stomatal ledges, occasional leaf
perforations, irregularly fused cell boundaries and glued leaf surfaces were noticeable in
the leaves of the polluted populations. Such were not observed in the non-polluted
populations. It was suggested that foliar morphology of these group of plants could serve
as phytometer to gauge the threats of power generators used in homes to terrestrial
ecosystem.
Key words: Domestic power generator, terrestrial environment, plant species
Introduction
The ever increasing human desire for comfort and good living standard as well as
industrial activities has warranted the use of cars, vehicles, power generating plants and
other mechanical and electrical appliances (AFF, 1953). All of these are capable of
generating phytotoxic air pollutants such as black carbon (carbon monoxide- CO),
Carbon dioxide (CO2), Sulphur dioxide (S02), Nitrogen Oxides (NOx) and
Peroxyacetylnitrates (PANs) (Bonnie and Joel, 2000; Socha, 2002).
These harmful gases are emitted into the atmosphere where they pollute the air, and as a
result of gravity, they are deposited on any living or non-living materials on the ground
either in powdery state or in solution state (Lenntech, 2005).
Air pollution is commonly experienced in major places such as busy roads with high
vehicular traffic, homes especially from emissions by domestic power generators and
industrial areas. Air pollutants in these places are capable of affecting plants by causing
damages to the cuticular and subcuticular regions of the leaves. These damages could
lead to the development of diseases and other problems on the affected plants (Pal et al;
2002 and Heather, 2003). Though the ecosystem has the capability to adjust to change
and maintain equilibrium yet, if anyone of the ecosystem components is substantially
altered due to natural or man made stress factors, the entire ecosystem can be affected
(Adela, 1990). Previous studies had revealed that many flowers and vegetable crops
suffered ill effects from air pollution caused by exhaust gases. Trees have also been killed
by pollution. Air pollution causes rubber tires on automobiles to crack and become
porous. Fine buildings become shabby, their walls blackened with soot as a result of the
pollution that has settled on building stones and surface for years.
This study presents the various cell alterations caused by gaseous pollutants on leaves of
plant species growing near the exhaust-pipe of power generators used in homes.
Materials and Methods
Collection of Plant Samples
Matured leaf samples of species of Euphorbia hererophylla, Chromolaena odorata,
Commelina difusa and Kyllinga pumila were collected from within 0.1 - 0.25m radii of
the exhaust–pipes of power generators used for domestic purposes especially by the elites
in Benin City, Edo State, Nigeria. Another collection of same species were made in the
same environment, but at distances of 100-110m away from the power generators.
The first set of collections represented the polluted populations, while the second set
represented the non-polluted populations which served as control for this study.
Leaf Dimension
Ten (10) leaves per species from the polluted and non-polluted areas were randomly
selected, their sizes were measured with the aid of plastic ruler and the data were
recorded.
The Leaf Area (LA) of each leaf was then determined according to Duncan and Hesketh
(1968), Remison and Lucas (1982) as:
LA: L x W x 0.75
Where, L = Length of Leaf
W = Width of Leaf
0.75 = Constant
Preparation of Slides
The epidermal peels of each leaf sample were obtained using the methods of Metcalfe
and Chalk (1988) and Olowokudejo (1990). The leaves were placed, with the outer
surface facing downward, on a flat surface and flooded with 8% sodium hypochlorite
solution (NaOCl). An area of about 1cm square was removed from a central / standard
position, always midway between the base and the apex of the leaves. The peels were
mounted temporarily on slides. 10 slides (each of adaxial and abaxial surfaces) were
prepared per population.
Measurement of pores, guard cells and collection of data
The slides were examined under the light microscope using x20 and x40 objectives. Data
were collected from 10 microscopic fields selected at random from each slide. The length
and width of stomatal pores and guard cells were measured using ocular micrometer.
Data were collected from 25 stomata per leaf surface. This was done in 10 replications.
Line drawings of the epidermal cells, stomata and subsidiary cells were made at different
microscopic objectives. The data obtained were subjected to relevant statistics using
mean, standard deviation and ANOVA. Significant differences were determined at p <
0.05.
Results and Discussion
The average leaf areas (cm2) of the plant samples from polluted and non-polluted sites
were shown in Table 1 while their leaf epidermal features are summarized in Table 2.
Illustrations of the epidermal features were shown in Figures1-4.
The average leaf areas for the polluted and non-polluted populations of Euphorbia
heterophylla were 2.60 + 0.1 and 4.18 + 0.7 respectively, while the average leaf areas for
the pollution and non-polluted populations of Chromolaena odorata were 14.16 + 0.4
and 34.39 + 0.2 respectively. Similarly, average leaf areas of 5.19 + 0.8 and 7.51 + 0.1
were calculated for the polluted and non-polluted populations of Commelina diffusa
respectively. Whereas, Kyllinga pumila had average leaf areas of 1.80 + 0.8 and 10.76 +
0.3 for the polluted and non-polluted populations respectively.
Stomata were not observed in the upper epidermis of leaves of Euphorbia heterophylla
and Kyllinga pumila. However, stomata were observed in the lower epidermis (Figs. 1
and 4). Chromolaena odorata and Commelina diffusa showed presence of stomata in the
adaxial and abaxial surfaces of the leaves (Figs. 2 and 3). The stomatal pores in leaves of
all the polluted plant populations were plugged by soot which hindered their
measurements (Figs. 1a, 2a&b, 3a&c, 4a&c). On the other hand, the stomatal pores in
leaves of the non-polluted plant populations were open and measured 2.01 + 0.16µm and
1.02 + 0.10µm as mean length and width of pores for Euphorbia heterophylla, while 1.92
+ 0.71µm and 0.91 + 0.01µm were the mean length and width of Kyllinga pumila
respectively. In Chromolaena odorata, the mean length and width of stomatal pores in
the adaxial leaf surface of the non-polluted population were 1.99 + 0.82µm and 0.91 +
0.11µm, whereas, in the abaxial leaf surface, the mean length and width were 1.47 +
0.20µm and 0.70 + 0.40µm respectively. Also, the mean length and width of stomatal
pores in leaves of the non-polluted populations of Commelina diffusa were, at the adaxial
surface, 3.56 + 0.10µm and 0.80 + 0.01µm, while, at the abaxial surface, they were 2.56
+ 0.13µm and 0.35 + 0.15µm respectively.
The mean length and width of guard cells in the abaxial leaf surface of the polluted
populations of Euphorbia heterophylla were 2.88 + 0.12µm and 1.62 + 0.4µm whereas;
the non-polluted populations had 2.62 + 0.14µm and 1.59 + 0.16µm respectively. In the
abaxial leaf surface of the polluted populations of Kyllinga pumila on the other hand, the
mean length and width of guard cells were 2.44 + 0.41µm and 1.47 + 0.69µm while, in
the non-polluted populations, the guard cells measured 2.91 + 0.05µm and 2.09 + 0.10µm
respectively. Similarly, the mean length and width of guard cells in the adaxial leaf
surface of the polluted populations of Chromolaena odorata were 2.84 + 0.25µm and
1.74 + 0.21µm while in the abaxial leaf surface, they were 2.02 + 0.36µm and 1.47 +
0.24µm respectively. The non-polluted populations of this species on the other hand, had
guard cells which measured, at the adaxial leaf surface, 2.86 + 0.51µm and 1.47 +
0.92µm as mean length and width respectively but in the abaxial leaf surface, the mean
length and width of guard cells were 2.81 + 0.01µm and 1.76 + 0.54µm respectively.
The mean length and width of guard cells in the adaxial leaf surface of the polluted
populations of Commelina diffusa were 3.62 + 0.10µm and 1.74 + 0.11µm while in the
abaxial leaf surface they were 3.46 + 0.14µm and 1.72 + 0.21µm respectively. In the non-
polluted populations of this species on the other hand, the mean length and width of
guard cells in the adaxial leaf surface were 4.15 + 0.14µm and 2.17 + 0.05µm, whereas,
in the abaxial leaf surface they were 4.06 + 0.50µm, and 2.88 + 0.08µm respectively.
The nature of the epidermal cell walls in leaves of both populations of Euphorbia
heterophylla was straight in the adaxial leaf surfaces but sinuous in the abaxial surfaces
(Fig.1). In both surfaces of the two populations of Kyllinga pumila, the epidermal cells
walls were straight but in the adaxial epidermis of Chromolaena odorata, they were
slightly sinuous in the two populations but sinuous in the abaxial surfaces of both
populations. Also, the epidermal cell walls in the adaxial and abaxial leaf surfaces of the
polluted populations of Commelina diffusa were straight but were straight and sinuous in
the adaxial and abaxial surfaces in the non-polluted populations.
Deposits of soot particles were observed in most of the epidermal cells, guard cells and
cell walls in the adaxial and abaxial leaf surfaces of the polluted populations of the
species. The soot particles tend to obscure and damage most of the epidermal features in
the leaf surfaces as they glued both surfaces of the leaves. Occasional perforation and
eroded epicuticular wax were other observed damages on the leaves of the polluted
populations. Conversely, the soot particles were not observed in the epidermal cells of the
non-polluted populations of same plant samples and their leaves appeared undamaged.
TABLE 1: Average Leaf Area (cm2) of plants from polluted and non-polluted populations
S/No
Species
Populations*
Polluted
Non-polluted
1.
Euphorbia heterophylla
2.60+0.1a
4.18+0.7b
2.
Chromolaena odorata
14.16+0.4a
34.39+0.2b
3.
Commelina diffusa
5.19+0.8a
7.15+0.1a
4.
Kyllinga pumila
1.80+0.8a
10.76+0.3b
* Figures with same letter in each row are not significantly different at 0.05 level of significance.
TABLE 2: Leaf epidermal characteristics of the plant species from polluted and non-polluted
populations.
Descriptions
Surface
Mean length
of pore (µm)
Mean width
of pore(µm)
Mean length
of guard cell
(µm)
Mean width
of cell(µm)
Nature
of
epidermal
cell wall
U
L
A
B
U
Euphorbia
A
-
heterophylla
B
-
Chromolaena
A
Plugged
odorata
B
1.99+0.82
Commelina
A
Plugged
diiffusa
B
3.56+0.10
Kyllinga
A
-
pumila
B
-
L
U
Plugged
-
2.01+0.16
-
Plugged
Plugged
1.47+0.20
0.91+0.11
Plugged
Plugged
2.56+0.13
0.80+0.01
Plugged
-
1.92+0.71
-
L
U
Plugged
-
1.02+0.10
-
Plugged
2.84+0.25
0.70+040
2.86+0.51
Plugged
3.62+0.10
0.35+0.15
4.15+0.14
Plugged
-
0.91+0.01
-
L
U
2.88+0.12
-
2.62+0.14
-
2.02+0.36
1.74+0.21
2.81+0.01
1.47+0.92
3.46+0.14
1.74+.011
4.06+0.50
2.17+0.55
2.44+0.41
-
2.91+05
-
L
U
1.62+0.41
Straight
1.59+0.16
Straight
1.47+0.24
Slightly
Sinuous
176+0.54
Slightly
Sinuous
1.72+0.21
Straight
1.47+0.69
Straight
2.09+0.10
Straight
L
Sinuous
Sinuous
Sinuous
Sinuous
Straight
2.88+0.08
Straight,
Sinuous
around the
veins
Anticlinal:
Straight
Periclinal:
Sinuous
Straight
Straight
=
=
=
=
Upper epidermis
Lower epidermis
Polluted Populations
Non-Polluted Populations.
Fig.1: (a) The abaxial epidermis of Euphorbia heterophylla from polluted area in Benin
City, Nigeria x400. (b) The abaxial epidermis of E.heterophylla from non-polluted area in Benin City
x400. (c)The adaxial epidermis of E. heterophylla from area polluted area in Benin City.x200. (d) The
adaxial epidermis of E.heterophylla from non-polluted area in Benin City.x400
Fig.2: (a) The abaxial epidermis of Chromolaena odorata from polluted area in BeninCity x400. (b) The abaxial epidermis of C. odorata from non-polluted area in Benin
City x400. (c) The adaxial epidermis of C.odorata from polluted area in Benin City x400
(d) The adaxial epidermis of C. odorata from non-polluted area in Benin City.
x400.
Fig.3: (a) The abaxial epidermis of Commelina diffusa from polluted area of Benin City x200. (b) The
abaxial epidermis of C. diffusa from non-polluted area in Benin City x400.
(c) The adaxial epidermis of C. diffusa from polluted area in Benin City x200. (d) The adaxial epidermis
of C. diffusa from non-polluted area in Benin City x400.
Fig. 4: (a) The abaxial epidemis of Kyllinga pumila from polluted area in Benin City x200. (b) The
abaxial epidermis of K. pumila from non-polluted area in Benin City x400.
(c) The adaxial epidermis of K. pumila from polluted area in Benin City x400. (d) The adaxial epidermis
of K. pumila from non-polluted area in Benin City. x400.
Plant samples collected within 0.1-0.25m from the exhaust-pipe of power generators used
in residential area showed reduced leaf size, plugged stomatal apertures blurred
epidermal surfaces and obscured cells (Tables 1-2 and Figs.1-4) These alterations might
be attributed to the activities of soot particles (Black carbon) and other gaseous pollutants
from the incomplete combustion of fossil fuel which the plant species were continuously
exposed to, since these features were not observed in the non-polluted populations of the
same species. These observations tend to confirm the previous assertions by Heather
(2003) and Mandal and Mukherjee (2001) that harmful gaseous air pollution cause
reduction in leaf size, plugged stomatal pores and injure plants leaves.
Domestic power generators being stationary sources of toxic air pollutants emit harmful
gases including soot particles (Black Carbon) directly onto any object located very close
to their exhaust-pipes. During the field sampling, soot particles were found covering the
leaf blades and parts of the stems of affected plants. Consequently, the affected portions
appeared black.
It is suspected that the black soot particles on the samples would have some negative ecophysiological effects, such as the screening out of solar energy (sunlight) and prevention
of carbon dioxide assimilation in them. These would hinder photosynthetic, respiratory
and transpiratory activities in the plants. This assertion is further buttressed by the fact
that these plants possessed leaves that were poorly developed and had reduced leaf sizes.
Whereas, similar plant species sampled from the non-polluted areas, showed proper leaf
development with large leaf sizes (Tables1-2). This observation tends to support the
previous assertions of Adela (1990) that air pollutants injure plants by damaging their
foliage and impairing the process of photosynthesis (Food making). It further supports
the assertions of Garner (2002) that high concentration of sulphur dioxide, nitrogen
oxides and ozone in the atmosphere can affect plant growth and reproduction. They are
capable of inhibiting photosynthesis carbon (sugar) production, alter carbon allocation to
roots and stems, reduce carbohydrate formation of mycorrhizae, uptake of important
minerals, root and stem growths.
Results from this study (Tables 1-2) revealed that the polluted leaves were smaller in area
than the non-polluted leaves in all the species sampled. The small nature of the leaves
might debar them from capturing enough amount of light as the larger non-polluted
leaves will do. It is further suspected that the deposits of soot particles and gaseous toxins
in the leaf epidermis in the polluted population could initiate chemical reactions with
moisture and to produce complex acids. This is pertinent, since Adela (1990) had earlier
asserted that SO2 and Nitrogen oxides may enter leaves and then react with cell moisture
to form complex acids. From the results, it is suspected that the damages and aberrations
on the epidermis (Figs 1-4) of leaves in the polluted populations were caused by the
gaseous air pollutants they were subjected to, since the non-polluted population did not
show such damages and aberrations in their leaves. This further support the reports of
Edwardo (2002) that air pollutants bind to plasma membranes, alter metabolism, destroy
stomatal apertures, damage chloroplast thylakoid membranes,erode epicuticular wax,
destroy epidermal cells and inhibit photosynthesis.
In conclusion, the leaves of the plant species used for this study had expressed the threat
of domestic power generators which they were exposed to, by showing various forms of
damages and aberrations reported in this investigation. It could, therefore, be inferred that
damages and aberrations resulting from gaseous pollutants will only be experienced by
plant species growing at 0.1-025m to the exhaust-pipe of power generators and not those
growing at 100-110m away from power generators. It is believed that the damages and
aberrations which are the major threats exhibited by the species investigated in this study
could serve as base line information of what would happen when species are exposed to
air pollutants from power generators while the plant species could serve as phytometer to
gauge the threats of power generators used in homes to terrestrial ecosystem which
basically has plant species as its major components.
It is, therefore, recommended that the Governments of Edo State and Nigeria in general
should improve on electricity supply so as to reduce the rate at which her citizens use
alternative source of power supply especially generators as they are capable of emitting
harmful gaseous substances into the environment.
Urban agriculture should be discouraged in residential areas where power generators are
used for domestic purposes. Crops growing in such areas are liable to black soot
particulates which could be deposited on their leaf surfaces. This will hinder their
photosynthetic activities and consequently affect other physiological activities of the
crops. If on the other hand urban agriculture is a necessity, the crops should be at least
100m away from the location of domestic power generators in the environs.
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