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Department of Botany, University
of Karachi, Karachi,
75270, Pakistan.
*Corresponding author e-mail:
kabir_botany82@yahoo.com; shafiqeco@yahoo.com
Abstract
A study was conducted during July 2008 to May 2009 to investigate the effects of traffic density and climatic conditions on the growth of Samanea saman (Jacq.) Merr., growing along different polluted roads of Karachi. Reduction in growth parameters such as leaf area, leaf fresh and dry weight, pods length, breadth, weight, seed length, breadth, weight and number of seeds per pod of S. saman were recorded at University Campus, University road, Board office road, Shaheed- e-millat road and Shahrah-e-Faisal during different seasons of the year. Some visual observations as canopy, fruit, seed production and leaf color were also recorded periodically which showed variation at different sites. Results indicated that S. saman at control site are growing as fast as they are given the favorable resources such as climatic factors which includes heat index, chill, humidity, temperature and wind speed available to them but road-side pollution stressed the growth. Climatic conditions were comparatively different on the city roads as compared to University Campus. The automobiles density has significantly (p<0.05) reduced the leaf area of S. saman at Shahrah-e-Faisal in summer season. This might be that during summer, growth was already slow, therefore the effects of pollutants on plants were more pronounced. These findings demonstrated that traffic density and harsh climatic conditions showed poor appearance and reduction in the reproductive parts and biomass of S. saman.
Introduction
The city of Karachi
is characterized by high density
of population and automobiles due to largest
industrial activities. Karachi
city is suffering by a series of environmental problems
due to constant increase in population growth,
automobiles activities, burning
of solid waste, domestic fuel burning and industrial activities. Transport system in the city comprises on buses, minibuses, rickshaws, cars, trucks,
motor cycles and locomotive trains.
The traffic system
in the city is not only noisy but also producing hazardous
environmental effects on human and plants. Most of the automobiles emit black smoke due to incomplete
combustion of fuel. Toxic materials such as carbon particles, unburned and partially
burned hydrocarbons, fuels, tar materials, lead compounds and other elements which are the constituents of petrol
and lubricating oils deposit on the surface
of plants. These pollutants in combinations cause greater or synergistic effects
to plants (Qadir & Iqbal, 1991). The uncontrolled growth in urbanization and motorization generally
contributes to an urban land use and transportation system that is environmentally unsustainable (Qureshi & Huapu, 2007).
Samanea saman (Jacq.) Merrill belongs to the family Leguminosae and sub-family mimosoideae, commonly known as rain tree having 25 m height with rough bark and bipinnately compound, alternate leaves with four to seven pinnae. Each pinna bearing two to eight pairs of dark green leaflets of 1.5-6.0 cm length. Flowers seasonally, mostly in spring and summer; flowers many, borne in axillary, flat-topped heads. Corolla funnel- shaped, of five fused petals 7-12 mm long, pink with greenish or yellow tips, and many red stamens 2.0-3.5 cm long. Fruit a sausage-shaped pod 6-20 cm long with thickened seams (Whistler, 2000). S. saman occurs from near sea level to an elevation of 700 m, cultivated and sometimes abundantly naturalized along roadsides, on river banks and in forests (Smith, 1985).
Urban greening
and urban forests
are particularly critical
to healthy cities in developing countries that contain
some of the world's largest
metropolitan areas. Urban green space that includes
contiguous vegetated areas such as parks, forest stands,
isolated trees growing along streets, in street medians, or on
private property, is a critical
foundation for both a healthy
population and healthy
economy in any city (Thaiutsa
et al., 2008). World Health Organization recommends at
least 9 m2 of urban green space per capita to mitigate a number of undesirable environmental effects and provide
other benefits (Deloya, 1993).
Different types of pollutants with varying nature
had a wide range of ill effects
on plants both quantitatively and qualitatively. The damage has been
increased considerably from the last few years. The pollutants released from vehicular exhaust emission have brought
changes in growth form of the plant species growing
close to the busy roads of the city and could involve
in the extinction of some important species.
Excessive amount of toxic element
usually caused reduction
in plant growth (Prodgers & Inskeep, 1981). Roadside
trees in the city are under pressure and are lost due to vehicular-traffic infrastructure and other community needs (Jim, 1998). Exhaust gas emissions from road traffic have been found to
damage vegetation growing in the
vicinity of roads and highways (Banerjee et al., 1983; Kammerbauer et al., 1986; Sauter et al., 1987). Adverse impacts of air pollution
on vegetation around industrial sources
and metropolitan cities
have been reported
by Iqbal et al., 1994; Emberson,
et al., 2001; Shafiq
& Iqbal., 2003; Shafiq et al., 2009
etc. Lead treatments at 25 to
125μmolL-1 produced significant effect on shoot, root and seedling length of Albizzia lebbeck as reported by Farooqi et al.,
2011. Samanea saman also
showed reduction in seed germination and seedling growth due to toxicity when treated with different
concentration
(25 to 100 ppm) of copper (Kabir et al.,
2011). The Neem (Azadirachta
indica A. Juss.) tree thus comes out to be capable of doing well under environmental stress and may, therefore, preferred
for plantation in the polluted
areas (Iqbal et al., 2010). Plants not only have an ornamental function
in urban areas, but they may also improve the quality of urban life (Akbari, 2002; Brack, 2002). Moreover, plants can uptake and accumulate pollutants through
their roots and leaf surfaces
(Sawdis et al., 2001) in particular, leaves
can act as biological absorbers of pollutants (Gratani
et al., 2000; Pal et al., 2002).
Industrialization,
urbanization, economic growth and associated
increase in energy demands have resulted in a
profound deterioration of urban air quality. Modernization and enhanced industrial activities led to the increased
use of fossil fuels and their derivatives, particularly in developing countries (Karar & Gupta,
2006). Combustion emissions and their contribution to ambient particulate, semivolatile, and gaseous
air pollutants all contain organic compounds and heavy metals that
induce toxicity, mutagenicity, genetic
damage, oxidative damage,
and inflammation (Lewtas,
2007). Industrial area soil and vegetation
showed variation due to discharge of various
types of pollutants Kabir et al.,
(2010). The retention and presence of these pollutants in and surrounding the industries greatly
decreased the habitat potential for flora of the region.
The aim of the present study was to investigate the effects of traffic density on qualitative and quantitative characteristic of S. saman growing in the polluted environment of Karachi city. Such studies may be helpful in selecting the tolerant species to pollutants which are capable to withstand the environmental stress and may therefore be introduced in the polluted areas.
Materials and Methods
The study sites selected were University Campus as Control while Board Office Road, University Road, Shaheed-e-Millat Road and Shahrah-e-Faisal as polluted roads. Traffic density of each road was recorded during different seasons. Number of different types of vehicles was observed for 6-hours per day as observations were divided into Morning, After-noon and Evening hours. Similarly climatic data of different roads for same hours were also recorded using the Kestrel 4000 NV Pocket Weather Tracker. Total number of vehicles per hour was recorded for different roads.
The plant materials influenced by the traffic
emission were obtained
from the road edge at a distance
of 1-3 meters at the
beginning of each season. Twenty
five fresh leaf samples of S. saman were
collected randomly from each area at 2-5 meters height
through out the plant canopy
to give respective average sample. Quantitative
characters of the leaves such as leaf length,
breadth, area and dry weights
were recorded during different seasons.
The fresh weight
of leaves was taken and the samples
were kept in an oven at 80 0C for 24 hours and oven dried weight of leaves was
obtained by electrical balance.
Similarly, twenty five samples of
pods were collected from S. saman randomly. Quantitative characters of the pods such as pod length,
pod breadth, pod weight with seeds, without seeds and seeds length, breadth,
seed weights were also recorded
during different seasons.
All measurements were based on three replicates.
ANOVA test was applied to the data to determine the significance of differences between sample means; values obtained from differently polluted study sites are to be compared with the respective value from the reference site. The data obtained were also statistically analyzed by Duncan's Multiple Range Test using SPSS version 13.0 on personnel computer at p<0.05 level.
Results
Effects of traffic density of different polluted roads of Karachi city on visual characteristics and growth variables of S. saman were studied. Different vehicles, which contribute pollution were recorded on some selected roads. These vehicles include trucks, tankers, buses, mini buses, cars/pickup, rickshaws and motor cycles.
The number of vehicles
was high on Shahrah-e- Faisal,
recorded as 4011/h during the month of July 2008, 4169/h for the month of November,
2008 and 3957/h and 4304/h vehicles were recorded
on the same Shahrah during February and May, 2009, respectively (Table 1). For other city roads there was significant (p<0.05) reduction in number of vehicle during different seasons
of the year and this reduction of vehicles was more
prominent for University Campus as compared to city roads. On the University road, high number
of vehicles was recorded as
compared to Board Office and Shaheed-e-Millat roads (Fig. 1). Data reveled
that on Board Office road during the month of July, 3494/h vehicles were recorded which
increased to 3598/h
for the month of November,
2008 while, during
February and May, 2009 the number of vehicles were 3321and 3316/h, respectively. Less traffic density
was recorded at Shaheed-e-Millat road during July and November, 2008 and February and May, 2009 as compared
to all other sites which
indicated that it may be less polluted road as
compared to other study roads of the city. During
the same months, numbers of
vehicles were also noted at the University Campus.
Data recorded of different periods
of the year showed that number of vehicles passed per hour on different
city roads were high as compared to number of vehicles recorded
at the University Campus.
Meteorology parameters during sampling periods were also determined. Climatic factors which include heat index, atmospheric humidity, chill, atmospheric temperature and wind speed were recorded during different seasons of the year showed that these parameters were higher for the month of July, 2008 and May, 2009 as compared to when they were recorded in November, 2008 and February, 2009. City roads showed high values for these climatic variables as compared to that which was recorded at the University Campus (Tables 2-4).
Visual characteristics of plant species recorded during different seasons of the year on different roads showed diverse effects on growth of S. saman. Different parameters which include phenology, leaf area, leaf fresh and dry weight, pods size, number of seeds per pod, seed length and breadth of plants species were affected greatly by auto emission on Shahrah-e-Faisal as compared toother city roads and University Campus. S. saman showed its visual characteristics favored by environmental factors which were indicated by its thick canopy and dark green leaves (Fig. 2). It starts its flowering in May and seed production occurs during July. Fresh pods and seeds were present on plants when it was studied in July, 2008 on the University Campus, while process of pods and seedproduction was slightly delayed on polluted road sites. Leaf color was dark green at University Campus while on road sites, green and dusty leaves were observed. Flower colour was recorded as whitish pink and more flowers were noted at University Campus and Shaheed-e-Millat road (Table 5). Fresh pods and seeds were observed in S. saman during July which exists even during November,2008. Leaves of S. saman collected during July and November, 2008 from Shahrah-e-Faisal showed a significant (p<0.05) reduction in their leaf area. During July this species was observed with seed formation at the University Campus but on city road sites most of the plants were at flowering stage because of their reduced growth on city roads with increased level of pollution.
During July, 2008 leaf area of S. saman at the University Campus was determined as 9.53 sq cm which increased during November, 2008 up to 10.40 sq cm indicated
that after flowering
and seed production periods its growth
is enhanced up to some extent due to rain in August and September-2008. On different polluted
roads of city, low leaf area was found especially on Shahrah-e-Faisal as compared to University Campus.
Leaf area at University road was
5.21 and 6.66 sq cm for the month of July and November, 2008, respectively while for February
and May, 2009 it was recorded as 8.63 and 5.48 sq cm respectively. Low leaf area (4.86 sq cm) was found during July on Board Office road probably due to low atmospheric moisture
contents which increased to 6.69 sq cm for the month
of November, 2008 and 8.84 sq cm for February,
2009 while it decreased again
for May, 2009 up to 5.71 sq cm. Same results were shown
by this species when observed
on Shaheed-e-Millat road. Leaf dry weight indicated that low dry weight was recorded during the month
of July at all the city and University Campus as compared
to November, 2008 and February
and May, 2009 (Table 6). S. saman pods and seed length
was also declined
in polluted roads of the city as compared to University Campus
(Tables 7 and 8). During
July, 2008 more reduction was recorded in pods and seed lengths,
pods and seed weight as compared to pods and seed concerned
parameters recorded in November, 2008. Results indicated
that on the polluted roads, plant growth was significantly (p<0.05) inhibited by vehicular emission.
Discussion
In this study we investigated the effects of traffic density
and climatic conditions on S. saman using leaf and reproductive materials collected from the polluted
and less polluted sites of the city. The effects of traffic density and climatic conditions on S. saman varied from site to site. Emissions from auto exhaust
have a detrimental effect on plants growing
in the area. Developing regions often face critical air pollution
problems due to the rapid growth of transportation and industry sources (Bell et
al., 2006). The study suggested that
increase in global temperature as a result of climate change may worsen the harmful effects of pollution on plant diversity. Most of the growth parameters were enhanced during February showing
that climatic factors
are also important
for increase or decrease of growth along with pollution
which normally suppressed the growth of most plant species. Better growth and productivity
during spring season is commonly observed due
to the influence of environmental variables (Baydar & Erbas, 2005). Longer photoperiod (16 h)
accelerated the plant development such as seed germination, initiation and growth pattern
of leaves and floral bud induction (Connor
& Sadras, 1992). Temperature is an important
climatic attribute affecting leaf emergence, leaf area and plant height (Kaleem et al., 2009). Any change in ambient climate strongly influences the morphological and quantitative variables
including plant height,
head diameter, achene number
per head, achene weight and oil contents
in sunflower (Killi et al., 2005).
Plants grown at two different
environments showed differences in shoot growth
rate (Hendrickson et
al., 2004).
Increased levels of pollutants caused a decline
in species richness.
However, the effects
are also depending on the type of polluters and the
plant species. The present
findings are supported
by Hussain et al.,
(1989) and Shah et al., (1991), who observed that road side plants generally
grow unhealthy. In addition, warmer and more humid climatic
conditions may intensify
the mobility and toxicity of the pollutants. One of fundamental effects may be changes in plant phenology
which is indicated
by interactions between
temperature and photoperiod (Bale et al., 2002).
Plant phenology is dependent upon environmental factors (Pillai et al., 1995). Higher temperature not only promotes but also hastens germination (Khalifa et al., 2000). So phenology
is an easily observed trait that responds
to climate change and allows us to predict vegetation adjustments and future tendencies in ecosystems in response to climate change by environmental pollution (Penuelas &
Filella 2001; Badeck et al., 2004). The plants growing
adjacent to roadsides of the city exhibited considerable damage in response
to automobile exhaust
emission (Iqbal & Shafiq, 1999; Shafiq
& Iqbal, 2005). Of all the plant parts, the leaf is the most sensitive part to be affected by air pollutants. The
sensitivity rests on the fact that the major portions of the important physiological processes are
concentrated in the leaf. Therefore, the leaf at its various
stages of development, serves as a good indicator to
air pollutants (Shafiq et al.,
2009). Pollutants derived
from the autoemission can directly affect the
foliage of plants by entering the
leaf, destroying individual cells, and reducing the plant ability to produce food. Reduction in leaf length, width and leaf area of roadside plants
was the witness of ill effects of the city environment. It
was found that the plants growing
on the Shahrah-e-Faisal are highly affected by autoemission. The inhibitory effects
on the growth of plants are due to the presence of toxic material
in the autoemission. The air pollution interferes with the seasonal variations, which takes place in
plants. Time of flowering,
senescence, shed of fruit, maturation of fruits and emergence of new leaves,
all these processes
are disturbed by air pollution
(Bhatti & Iqbal, 1988).
A major source of air pollution in urban areas is the combustion of diesel and gasoline fuels in cars, buses, trucks
and other on-road
transportation sources (Anon.,
2004). The presence
of various types
of pollutants derived
from automobiles might be responsible for the reduction
in leaf dry weight of S. saman. Less leaf dry
mass of all the plants at Shahrah-e-Faisal might be due to carbon exchange becomes limited and hence photosynthesis reduced. Therefore, reduction in leaf fresh and dry weight is directly related to different types of pollutants which are released into the environment by auto exhaust. The leaf areas, leaf dry and fresh weights of polluted road side plants were greatly reduced. Our finding agree with those of Sibak & Gulyas (1990); Iqbal & Shafiq (2001) and Shafiq & Iqbal (2003, 2005) who reported reduced leaf size due to air borne pollutants derived from automobiles. The productivity of a plant mostly depends on the rate of photosynthesis and respiration but on Shahrah-e-Faisal all these processes were disturbed which resulted in reduction of growth and biomass production. Even in areas where pollutant emissions are within the limits set by legislation, the study suggests that these contaminants could become more harmful to plant communities as the climate warms and changes (Zvereva et al., 2008). There is a need to draw a special attention on the protection of the environment by all segments of the society on urgent basis. Our efforts can be fruitful for healthy environment by making an effective policy and sharing the experiences of environmental friendly organizations working in developed countries of the world.
Acknowledgements
Authors are grateful to Higher Education Commission (HEC), Pakistan for the financial support of this study through project No. 20-1073/ R & D/07. The assistance of Mr. Zia-ur-Rehman Farooqi for data collection and analysis is also acknowledged. We also acknowledged the kind help of Dr. Ghulam Rasool Sarwar, Assistant Professor and Head of the Department of Botany, Government Degree Science & Commerce College, Orangi Township, Karachi, who suddenly died on 14th June, 2012 due to severe heart attack. May Allah Almighty shower His blessings upon the departed soul. Ameen.
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(Received for publication 21 September 2011)