Air Pollution and Plants By Abhishek Swami

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By Abhishek Swami

Rise in population, urbanization and expansion of the Greater Noida City has resulted in the considerable increase of Vehicular traffic, vegetation in the urban area, which functions as breathing lungs for the city environment, show symptoms of air pollution stress.

In India, vehicles fleets are old and poorly maintained, roads are narrow and thus increase in number of vehicles with two stroke engine is high, thus increasing the significant of motor vehicles as pollutant source. In fact, vehicle pollution is much greater that that caused by the emission of dust and poison gases by factories. Motor vehicles account for 60 – 70 % of the pollution found in an urban environment.

Although most people are aware that air pollution can affect their health, it is also true that these same pollutants can adversely affect the growth and reproduction of the plants and trees which make our environment so beautiful. Unlike people, plants are unable to escape from areas of high pollution and must try to grow and adapt to these polluted environments. Air pollutants impact a wide variety of vegetation, including crop plants, landscape plants, forest and native vegetation.

SOURCES OF POLLUTION

Air pollution is not only a regional problem but it regional problem too, and can affect the physical environment, human health and vegetation. There are many types and sources of pollutants. They can be broken down into broad categories such as mobile and fixed sources and natural sources. Mobile sources include motor vehicles such as cars, trucks, buses, trains and aircraft. A fixed source includes large industrial operations, refineries, numerous small industries which produce pollutant precursors, agricultural burning, dairy and cattle industries, and fertilizer production processes. Pollutants contributed by these source are known as primary air pollutants such as Sulphur dioxide (SO2), Oxides of nitrogen (NOx), Hydrocarbons and particulate matter etc.

Natural sources can also play a significant role in pollutant production. Volcanic activity can emit significant amounts of harmful pollutants into the atmosphere which can be distributed globally, fugitive dusts from non-vegetated areas or from agricultural operations are also important environmental concerns. Emission of organic compounds from trees and plants themselves are termed “biogenic emissions” and can contribute to formation of pollution in certain areas.

Pollutants are formed in the atmosphere when chemical components are interacting by sunlight; these are also known as secondary pollutants. These ‘photochemical’ reactions result in the production of various compounds including oxides of nitrogen (NOx), peroxyacylnitrates (PAN), sulfur oxides and aerosols, polyaromatic.

 

HOW PLANTS TAKE UP POLLUTANTS

Plants exchange atmospheric gases much like humans and animals breathe. However, plants take up carbon dioxide and give off oxygen which is opposite to ourselves. This production of oxygen is partially responsible for maintaining the oxygen atmosphere on the planet. Plants take up and release gases through small pores on the leaf surface called stomata. The uptake of carbon dioxide and conversion to carbohydrates and energy is called photosynthesis. During this process of uptake of carbon dioxide plants can also take up pollutants.

Once the pollutants enter the leaf, the pollutants may injure leaf tissue and upset the normal metabolic process of the plant. Depending on the pollutant, the upper or lower leaf surface of the plant will exhibit symptoms. Because the most common pollutants are gaseous (NOx, sulfur dioxide, PAN) and are broken down quickly within the plant.

Points

Injury to plant due to exposure of air pollution

 

1- VISIBLE INJURY:

Necrosis: Death and collapse of the plant cell.

Chlorosis: Loss or reduction of chlorophyll resulting in bleaching or fading of the leaf’s green color that makes the leaf to appear yellowish.

Abscission: Dropping of leafs

Epinasty: Downward curvature of the leaf due to higher rate of growth on the upper surface

2- INVISIBLE INJURY

Result of impairment of physiological and biochemical reactions. The most sever effects can occur on photosynthesis, respiration, photorespiration, nitrogen metabolism, pigment synthesis, enzyme structures and stomata response.

Vegetation injure due to a variety of other pollutants, including sulfur dioxide, nitrogen dioxide, Pan, ethylene, fluoride, chloride and ammonia. Sulfur dioxide is released as a by product of combustion processes from automobiles and through a variety of industrial activity. Sulfur compounds may impact plants directly, or may combine with water to form sulfuric acid particles. Symptoms produced by sulfur dioxide include a bleached appearance, typically white to tan in color, with symptoms appearing on the leaf edges and primarily between the leaf veins. Nitrogen oxides (NOx) are generated both by natural and man-made processes.

Mostly in urban areas, motor vehicles responsible for a large percent of NOx production and similar to sulfur compounds, NOx compounds can affect vegetation directly but also combine with atmospheric moisture to form nitric acid. A primary symptom would be chlorosis (yellowing) of leaves, or occasional bleaching.

Photochemical oxidants produce very distinct symptoms in plants; this injury in plants is usually seen on the lower leaf surface. The leaf underside typically appears silvery or bronze in color. No other pollutant causes injury symptoms similar to this. However, occurrences of Pan are infrequent and are usually restricted to areas near urban centers.

Many other problems can mimic pollution injury, including nutrient deficiencies, insect feeding, physiological stress (moisture, heat, and cold), and loss of photosynthetic pigments in plants such as chlorophyll and carotenoids, reduction of plant productivity, viral diseases and premature leaf fall.

 

Measures to reduction of plant injury and pollution:

There are very few measures that are available to protect vegetation. Specific chemicals have been developed to reduce the affect of certain pollutants, particularly ozone; these chemicals are extremely expensive and not effective enough widespread use. Most common approach to protect vegetation is genetic breeding of new varieties which are tolerant to pollutant levels. Although the best approach for limiting pollutant injury to plants is to simply reduce the amount of pollutants released into the atmosphere.

Education to common mass possibly one of the best approaches for reducing air pollution. As we introduce concepts of environmental protection in our school curriculum, students will become more educated and aware about pollution problems. As they mature into adulthood, these learned concepts may provide impetus for a more proactive stance on protecting our environmental resources, particularly the air. The most relevant to the subject is a Chinese perceptions abut education which says:

“If you plant for one year, plant rice, if you plan for ten years, plant trees

But

If you plant for one hundred years, educate the people”

Fig: Showing necrosis in mango leaf       

        (Damage leaf tissue)

 

Fig: Road side tree Leaf Covered with high concentration of dust

 

Fig: Yellow patch showing chlorosis (loss of plant pigments) in leaf

 

 

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