Effects of Railway Engine Emission on the Seedling Growth behavior of Woody Plant Species Acacia nilotica (Linn.) Delile

The vegetation growing close to the railway tracks are usually exposed to various types of toxic pollutant discharged from the locomotive diesel engines. In present studies, the seedling growth performance of Acacia nilotica responded differently in soils of Cantonment Station, Drighroad Junction, Malir Station and Landhi Junction as compared to Karachi University Campus (Control) soil. The seedling growth of A. nilotica (Linn.) Delile gradually increased in soil of Drighroad Junction, Malir Station and Landhi Junction. The seedling growth of A. nilotica in Cantonment soil was significantly (p<0.05) deceased as compared to the treatment of University Campus soil. The root, shoot, seedling lengths, circumference, root, stem and seedling dry weights of A. nilotica grown in soil of Cantonment Station showed significant (p<0.05) reduction as compared to University Campus. The growth parameters such as root, shoot, seedling lengths, number of leaves, leaf area, circumference, root, stem, leaf, seedling dry weights of A. nilotica grown in soil of Malir Station and Landhi Junction were significantly (p<0.05) enhanced as compared to University Campus soil. Keywords— dry weight, kikar, locomotive railway diesel engine, root, seedling growth, tolerance.


INTRODUCTION
Pakistan is a developing country and its urban cities are suffering by a series of environmental pollution problems due to increase in automobile and industrial activities [29]. The automobile activities is a major source of different types of pollutants such as suspended particulate matter, carbon monoxide, hydrocarbons (HC), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), peroxyacetyl nitrate (PAN) and heavy metals (Pb, Cd, Cr, Ni, Zn) in the environment. The addition of pollutants in soils nearby railway track might produce toxic effects on the biodiversity, trees and crops productivity. The diesel engines showed low concentrations of carbon monoxide and unburned hydrocarbons outlet as compared to spark ignition engines. Currently, the automotive manufacturing industries are facing the serious challenges to meet the future specific requirements for the regulation of both NOx and particulate emissions [19].
Karachi is the 22 nd biggest city of the world and is the largest city of Pakistan. It is situated at 64° longitudes and 27º latitude on the shore of Arabian Sea near the Indus River delta with main seaport of the country. The city covers an area of approximately 3,530 square kilometers with more than 18 towns and 6 cantonment boards. The transport system to carry goods and public in the city is comprises on locomotive train, trucks, buses, mini buses, cars, rickshaws and motor cycle which are the primary mode of conveyance. The railway track of Pakistan covers about 11, 755, 00 kilometers including double line track. The Pakistan railway consists of 12 steam locomotives, 16 electric locomotives and 500 diesel electric locomotives for the transport of goods and public Pakistan Railway, 2010-2011, [22]. 115 passenger and most of the cargo trains have been suspended temporarily due to fuel shortage (The Nation, September 29, 2011). According to Rizvi [28], 26 mail and express, 39 intercity, 33 passenger, 24 mixed, 03 international, 03 Karachi shuttle and 02 cargo trains are in operation from Karachi to other parts of the country.
Gasoline and diesel fuels are mixtures of hydrocarbons (made of hydrogen, oxygen carbon atoms). Diesel fuel is a mixture, which may contain approximately 400 distinct hydrocarbons and 20 organic compounds of sulfur and additives [21]. The level of environmental pollution with polycyclic aromatic hydrocarbons (PAHs) can be correlate with the region of industrialization and the traffic density. These PAHs accumulate in soil along the roads. PAH, contents found at the depths up to 2 meters. It was concluded that the plants can be absorb and decompose some PAHs which were mostly deposited in the soil, and some of them in the roots [31].
Railway transportation is an important mode of transportation [18] in Pakistan and all over around the world. The railway transportation, leaked cargos, fuel combustion, the use of lubricate oils and sleeper impregnation oils during railway transportation considered the main resources of heavy metals likewise Pb and Cd [5]. The impact of toxic pollutants near the railway track and railway stations on ecological point of view investigated by different researchers [6, 8 and 9]. Polycyclic aromatic hydrocarbons (PACs) and heavy metals ass essed in soil and plant samples collected from different areas of the railway junction Ilawa Glowna, Poland. PAH, contamination of soil and plants was reported highest in the platform area and near the railway siding and lowest in loading ramp and cleaning bay areas. Whereas, the heavy metal contamination pattern was different. The soil and plants were very highly contaminated in the cleaning bay and sidetrack areas while the loading ramp and platform areas were less contaminated [17]. The botanists carried out some studies for plants growing along the railway tracks for the last many years [33]. A floristic study in 246 areas along the railway tracks of Poland was carried out [11]. Railway ballast contains little organic material [15]. The exceed concentrations of fine particulate matter (PM2.5) levels, carbon dioxide (CO2) levels and particle number concentrations (PNC) against World Health Organization (WHO) permissible limit (25 µg/m 3 ) in train carriages on seven routes of the mass transit railway in Hong Kong were recorded [34].
The aim of the present study was to investigate the seedling growth behavior of an important woody tree species, Acacia nilotica (Linn.) Delile in the soil collected from near the different railway tracks sites of Karachi, city and compared with the soil of Karachi University Campus.

II MATERIAL AND METHODS Description of study site
Karachi faces many challenges from the last few decades due to rapid urbanization and industrialization. It is an important hub in economy of Pakistan due to its presence on the coast along the Arabian Sea situated at latitude of 24° 48' N and longitude of 66° 55' E. The study area covers about 20 kilometers from Cantonment Station to Landhi Junction (Fig. 1). The area was disturbed and affected from the activities of rail and road transport. The detail work regarding seedling growth behavior of Acacia nilotica in the past years is scanty.

B. Cantonment Station: Karachi Cantonment Railway
Station is situated at a latitude of 24° 50' N and longitude of 67° 02' E. Roads with high traffic congestion surround the area around the Cantonment railway station. The main express and local train arrives and depart from here for "up" and "down" side of the country. Most of the passengers use this railway station due to departure and arrival points of many trains. The mechanical diesel workshop at this station is also situated. The service facility is available at this station for cleaning and washing of coaches. Most of the cargo trains and extra coaches are parked at this station ( Fig. 2).  5).

Species description
Acacia nilotica (Linn.) Delile is a small to medium size tree with more or less rounded umbrella shaped crown and locally known as Kikar (Fig. 1). It belongs to family Fabaceae and sub-family Mimosideae. It is widely distributed in subtropical and tropical Africa from Egypt to Mauritania southwards to South Africa, and in Asia eastwards to Pakistan and India [3]. It is widely planted in arid and semi-arid regions of India and Pakistan [24]. A. nilotica is also a salt tolerant species and successfully adapted in arid environment [20]. The adult and juvenile plants easily regenerated from the base after removal of top growth and viability of seed remain more than five years [4]. The tap roots of A. nilotica rapidly penetrated deeply in soil and access soil moisture for successful growth that ensured the competition to other plants [16] and the seeds remain dormant for long periods due to the presence of hard impermeable seed coats [23]. A. nilotica rapidly grow up to 2-3 m in diameter and 15-18 m in height. The pods with 8-12 seeds, increased 7-15 cm in length with a necklace appearance [13]. A. nilotica is multipurpose leguminous nitrogen fixing tree which increased the soil fertility [2]. The seedlings of Acacia nilotica showed better growth regarding root, shoot and seedling lengths, number of leaves and circumference in soil of Drighroad Junction, Malir Station and Landhi Junction as compared to University Campus while, the seedlings grown in Cantonment Station soil showed inhibitory effects on root, shoot and seedling lengths, number of leaves and circumference ( Table 1) The dry weights of root, stem, leaves and cumulative seedlings of A. nilotica were recorded high for the seedlings which were grown in soil of Malir Station and Landhi Junction as compared to University Campus (Table 1). Table (2) showed a significant (p<0.05) increase in root dry weight of A. nilotica grown in soil of Drighroad Junction (0.064 g), Malir Station (0.113 g) and Landhi Junction (0.152 g) in comparison with University Campus (0.072 g). The seedlings of A. nilotica developed from the soil of Cantonment Station showed a significant (p<0.05) reduction (0.064 g) in dry weight. The stem and leaf dry weights of A. nilotica also showed a significant difference for the seedlings grown in soil of Cantonment Station, Drighroad Junction, Malir Station and Landhi Junction as compared to University Campus ( Table 2). The cumulative seedling dry weight of A. nilotica was recorded significantly (p<0.05) high for the seedlings grown in Drighroad Junction (0.833 g), Malir Station (0.931 g) and Landhi Junction (1.186 g), whereas the seedlings grown in the soil of Cantonment Station demonstrated a significant (p<0.05) reduction (0.494 g) as compared to University Campus soil (0.782 g). The root/shoot ratio of A. nilotica was significantly (p<0.05) different for the seedlings grown in Cantonment Station, Malir Station and Landhi Junction as compared to University Campus soil. Leaf weight ratio of A. nilotica showed a significant (p<0.05) difference only for the seedlings developed from the soil of Malir Station and Drighroad Junction as compared to the University Campus soil. The specific leaf area showed significant (p<0.05) difference in seedlings grown in soil of Cantonment Station as compared with University Campus. The leaf area ratio showed significant (p<0.05) increase (2.64 cm 2 g -1 ) in seedlings grown in Cantonment Station and Malir Station soil as compared to the University Campus.

IV.
DISCUSSION The influence of railway exhaust emission on the seedling growth of Accacia nilotica was investigated. Railway emission affected seedling growth of A. nilotica. A significant (p<0.05) reduction in seedling growth of A. nilotica raised in soil of Cant railway station observed. The routine works on railway tracks of Karachi is badly affected the soil properties near the railway tracks. The workshops for maintenance of vehicles, train engines and coaches also contaminated the soil of the area. The plants growth directly depends on the soil of the area in which they are growing, because the soil is the medium for plant growth, water and nutrient supplier and give support to plants [10]. In our previous studies the changes in physical and chemical properties of soil near the railway track of Karachi, city were recorded (Table 3a, 3b). The roots of plants penetrate in soil, which act as a water-holding tank and fulfill the needs of water for plants growth. The physical properties of soil such as compactness, structure, and texture and bulk density directly influenced the root penetration, growth performance and production of yield to different crops [12]. The nutrient availability, their absorbance and uptake from water to plants depend on physical attributes of soil [30]. The soil texture, bulk density, porosity and water holding capacity, organic matter, dissolved salts and available sulfates are affecting the plants growth [26].
The physical and chemical characteristics of University Campus, Cantonment Station, Drighroad Junction, Malir Station and Landhi Junction soils were different. The activities of automobiles at the above mentioned study areas are different and the rate of pollutants introduction in environment vary from area to area. The most polluted and disturbed area was Cantonment Railway Station and the less polluted area was Landhi Junction as compared to Karachi University Campus. The growth performance of Acacia nilotica, showed a significant (p<0.05) variation raised in different soils of the study area due to changes in physical and chemical nature. The height of A. nilotica was highly increased in soil of Landhi Junction whereas; in the soil of Cantonment Station height of A. nilotica was lowest. The lowest number of leaves and circumference were recorded in soil of Cantonment Station. Rehman [25] carried out similar studies in the polluted soils of Landhi and Korangi industrial areas of Karachi city. The height and number of leaves of Leucaena leucocephala showed discontinuous variation after every two weeks in polluted soils of Landhi and Korangi industrial areas [27].
The seedlings of A. nilotica grown in soil of Karachi Cantonment Station exhibited significant reduction in root, shoot and seedling lengths, number of leaves and circumference due to most contamination of repairing and servicing activities of train engine and coaches as well as some other activities in that area. The reduction in these parameters of different plants might be due to disposal of waste products and spent engine oil in the vicinity of Cantonment railway station. These findings were supported by Akoto et al. [1], who described that vegetation in the vicinity of railway servicing workshops in Kumasi city of Ghana was severely affected. The root, stem, leaf and seedling dry weights of A. nilotica seedlings grown in soil of Karachi Cantonment Station were significantly reduced as compared to University Campus, Drighroad Junction, Malir Station and Landhi Junction. The same results were coated by Iqbal and Shafiq [14], who described that the reduction in leaf number, plant height, circumference, root, shoot and total plant dry weights of Prosopis juliflora and Blepharis sindica were suppressed due to low contents of calcium carbonate, high electrical conductivity and high contents of sodium and potassium salts.

V CONCLUSION
The present study showed that the seedling growth of A. nilotica raised in the soil of different areas of railway tracks of Karachi responded differently due to anthropogenic activities, grazing, and construction of railway tracks and release of emission from railway engines. The soil of Cantonment Station was highly polluted due to repairing activities, release of exhaust from train engines, chemical used for rolling stock, exploitation (machine grease, fuel oils, and sleeper impregnation oil) and toxic substances processed by railway transport. If the exposure of pollutant on soil near railway tracks goes on then there would likely to be more damage to the vegetation changes in future.