Flowering plants have provided habitats on earth since more than 135 million years ago . Since their first appearance, they have had a crucial role in supporting and affecting other life.
Plants are source of fiber, fuel, shelter, and nutrition. During photosynthesis, they absorb carbon dioxide from the air and release oxygen, which humans and other animals need to breathe. Most plants are capable of removing pollutants from the environment through bioaccumulation and incorporating them in their tissues.
While these abilities are good news for us, as plants are helpful in mitigating impacts of pollution in the environment where we live, making it safer and cleaner, even they have their limits and get affected by pollutants to a varying degree. If you want to learn what is the effect of pollution on plants, keep on reading.
How does pollution affect plants in general?
Pollution is a widespread problem affecting the world as a whole. It comes in many forms including air, land, and water pollution and from a variety of sources including industry, commercial, and transportation sectors.
Some forms of pollution are clearly visible, other forms are invisible to the naked eye. Pollution does not only affect animals and humans, it has many negative effects on plants as well. As a matter of fact, plants reveal toxins in the environment sooner than their effects would show on our health.
This is because in most cases pollutants alter plant metabolism and make plant weak and vulnerable to disease or pest infestation. Some of the recognizable signs of these processes include leaf damage (yellowing, falling leaves or injuries), poor growth, root damage, and inability to photosynthesize properly which results in stunted growth and diminishing productivity.
Why are plants sensitive to different forms of pollution?
Plants are living organisms that depend upon several environmental factors for their survival. These include: appropriate amount of light and temperature, sources of nutrition, water, air, and physical space and preferred medium to grow (different types of soil or water).
To grow and reproduce, they take substances from their surrounding environment, from the soil and air via roots and leaves. Plants then use these substances for building body tissues and supplying body cells with energy for functioning. Through these metabolic processes, plants are processing elements that make their way to their proximity – including pollutants, as plants do not have the mobility like animals to avoid them.
Plants are sensitive and vulnerable to all forms of pollution. How much each plant will be affected depends upon numerous factors (for example on soil type, concentration of a pollutant, age of a plant, temperature, season, etc.) that differ from place to place or across plant species.
The negative effects of pollution on plants
The impact of air pollution on plants
Air pollution comes from many sources such as smokestack from factories, burning of fossil fuels for energy, emissions from transport, agriculture (livestock) or even fumes from paints, varnish, VOCs, or during the solid waste management such as waste incineration or gas leakage from landfills that are not sanitary.
The effects of air pollution on plants can be either direct or indirect.
Direct effect is when toxins harm plants by depositing on them directly from the air and affecting their leaf metabolism and uptake of carbon, which they need to build their body and get energy to live. The chemicals responsible for direct pollution include ozone and nitrogen oxides.
Indirect effect happens via soil and starts at the roots. Some air pollutants, like heavy metals (lead, cadmium, mercury) from industrial activities, fall on the ground and change soil chemistry and pH. Plants then have problems with obtaining enough nutrients they need to thrive.
Let’s have a look at how the most common air pollutants affect vegetation.
Effects of particulate matter or dust on plants
Particulate matter are very fine particles that get stirred in the air from different sources (industries, agriculture). Due to their small size, they can harm living organisms if the exposure is long term or severe. These particles can be for example a thin cement dust, carbon soot or magnesium-lime dust. In some areas with heavy industries, dust particles make up to 35 percent of air pollution suspended in the air .
Particulate matter does mechanical harm to plants. Small particles fall on the leaves and reduce light penetration or even block the opening of stomata, thus preventing their proper function. Smaller particles even enter stomata and interact with the biochemistry of plant metabolism this way . Things can get as far as actually preventing the plant from properly photosynthesizing.
Plants that are affected by this pollution could lose the most affected leaves or fade due to the inability to photosynthesize. Leaves can also sustain chemical injuries, lesions, if the deposited dust reacts with water from the environment. Alkaline dust turns to toxic for plants when reacting with water. Imagine that someone applies thick coating of irritative substance on your skin and you are unable to remove it. That is probably how plants feel in this situation, since they are unable to remove the dust coating.
During the long-term exposure plants are under stress. Some fruit trees like peaches and cherries, for example, experience shorter flowering periods and drop fruits too soon. Their overall productivity is reduced .
It is sad to know that plants suffer harm when exposed to dust because they are often planted in cities to filter the particulate matter pollution from the air. Their capacity to capture dust particles is astonishing and helps us greatly in making city air cleaner for us. For example, scientists have calculated that 300 Poplar trees spread over 2.5 acres filter out as much as 0.375 tons of dust during the summer .
Particulate matter also deposits on soils and some types change soil pH to the point where plants cannot thrive on them. For example, alkaline dust increases soil pH and changes its chemistry, which affects ability of plants to utilize nutrients. Such profound changes of the environment affect growth of whole crops, since they are usually one type of a plant (monoculture) on a large surface area.
Effects of photochemical smog on plants
Photochemical smog occurs during chemical reactions among nitrous oxides from industrial activities and VOCs originating either from vegetation or human activities. The chemical reactions are driven by sunlight, that’s why the name – photochemical smog. Everyone of us is probably even familiar with this type of pollution. Photochemical smog creates that orange haze over cities in the summer, which also correlates with the time when most plants are flowering.
One of the resulting products of these chemical reactions is ground level ozone, which has dangerous impact on vegetation. The profound effects are discussed in the following section.
Other harmful product is peroxyacetyl nitrate, which can be detected by bronzing or silvering of young leaves . Young plants that are just developing are weaker and have lower chances of survival when exposed to this contaminant.
Ozone pollution – the harmful effect of ozone on plant growth
The ground level ozone is formed when volatile organic compounds react with nitrogen oxides in the presence of sunlight. You can easily recognize the orange-tinged smog one sees in urban areas when nitrogen oxides and volatile organic compounds, emissions from industrial facilities, chemical solvents, motor vehicle exhaust or gasoline vapors cook together in the sunlight.
Ground level ozone is major pollutant that greatly affects terrestrial plants and does lot of harm to agricultural crops. So much that there have been numerous studies, which measure its effect on crops, carried out throughout the years. It is, for example, known that crops like soybean and peanut are more sensitive to ozone than corn or wheat.
Ozone damages plants by preventing photosynthesis and obstructing stomata, restricting respiration and stunting plant growth. When plants are exposed to this ozone throughout the season, they first exhibit signs of damage on their leaves in the form of tiny light and dark spots, later followed by bronzing and reddening. Later on, leaves turn pale due to the lack of photosynthetic activity (chlorosis) and may die out .
How acid rain affects plants?
One harmful pollutant that damages plants is acid rain. Acid rain is formed when one or both of sulphur dioxide and nitrogen oxides react with water, oxygen, and other chemicals in the atmosphere, process which often happens in the presence of fossil fuel combustion. This leads to the formation of sulphuric acid and nitric acid.
Acid rain comes in two main forms: wet and dry. Wet rain is any form of precipitation involving water, and could include snow, fog, hail, rain, or dew. Dry deposition occurs when acid particles are formed in the atmosphere in the absence of water. These can then attach themselves to particles in the air and are deposited on the ground during events such as dust-storms.
When acid rain reaches earth’s surface, it causes damage to the soil, water, and plants. Not only does direct exposure to acid rain directly damage plants, it damages leaves and makes it harder for the plant or tree to photosynthesize and regulate the exchange of gasses.
Acid rain also affects the quality of soils, as it pollutes them and indirectly damages plants by dissolving and washing away nutrients they need and minerals from the soil (for example, magnesium, sodium, potassium, and calcium) on which the plants rely.
When acid rain deposits in water, it’s pH drops, and water becomes acidic. Plants that are not tolerant to acidity would suffer immediately by not being able to utilize such water. Acid rain may also impair the efficiency of nutrient and water uptake by plants when changing chemistry of soils by mobilizing metals like toxic aluminum, which affects plant metabolism .
In the past, many forests suffered great losses due to severe acid rain exposure. Many trees died after becoming vulnerable to disease and pest infestation or even unable to withstand freezing weather when weakened by the effects of acid rain.
Water pollution toxicity to plants
Water pollution is degraded water, toxic for the flora and fauna. It occurs when harmful chemicals or microorganisms or waste or too much sediment contaminates sources of freshwater and groundwater. Water pollution happens in various ways, such as sewage leakage, industrial spills, direct discharge into water bodies, biological contamination, or farm runoff (including pesticides, fertilizers).
Plants need water to live, like us or other living organisms. 95 percent of the plant body is made up of water. Throughout plant’s life, water carries nutrients to different body cells (in fact, it is also responsible for maintaining the cell structure) and supports the process of photosynthesis .
When plants do not have enough water, their leaves curl up and the plant eventually die. If plants have too much water, they may die as well because their roots suffer of lack of oxygen and begin to rot. As you can see, a plant’s relationship with water is based on balance – they need just the right amount and the right pH (5.5 to 7.5) otherwise they suffer .
Contamination of water has many negative effects on plants that reflect this delicate relationship.
Sometimes there is an excess of nutrients in water, like in case of agricultural runoff with high concentration of nitrogen and phosphorus, which causes an excess in plant growth. Plants grow leaves and thin branches too fast, while their root system remains too undeveloped and cannot provide enough nutrients for plant to successfully mature and reproduce . After the initial green boom, plants become weak and vulnerable to disease or weather.
Other times this excess in nutrients in the water causes a fluctuation in biochemistry and damages or kills the plant by changes in availability of nutrients and chemical properties of soils where they grow. Soil pH becomes either too acidic or alkaline. Both of these changes in soil chemistry decrease availability of nutrients to plants. In this case, plant leaves turn yellow and brown on the edges. Eventually, damaged leaves will fall off.
For example, pH higher than 7.5 could lead to insufficient intake of iron. Plants deprived of iron experience iron chlorosis. Iron deprived plants have yellow leaves with dark green veins. Over time, leaves could turn to white .
Soil pollution effects on vegetation
Sources of soil pollution can be direct, for example, from dumping toxic chemicals directly on to a site, or indirect like deposition of toxic chemicals from particulate matter that come from air pollution.
Air pollutants can travel long distances and do not respect any boundaries or regions of a special ecological significance. It can be surprising how far particles can actually travel when blown with the wind. They can contaminate soils even hundreds of miles away from the origin of pollution. Acid rain also belongs to soil pollutants that affect plant life.
Direct sources of land pollution come from improper waste disposal, from sources like oil spills, landfills, pesticides, or illegal dumping. Some of the most common pollutants are microplastics, petrochemicals, solvents, lead, asbestos, common pesticides and herbicides (glyphosate).
Plants get affected when toxic chemicals seep into the soil and strip the land of nutritional content. These harmful substances often accumulate in the soil, changing its chemical properties and availability of other elements, which damages plant cells and prevents them from obtaining nutrients and thriving.
One major contaminant that accumulates in soils is a heavy metal, lead. High concentration of lead in the soil leads to decreased availability of other metals, which are needed in the right amounts for plants’ health. In severely affected plants, lead inhibits photosynthesis. Plants do not prosper and eventually die.
In other cases, plants get poisoned by toxic substances stored in contaminated soils. For example, pesticides, that leak to vegetation surrounding agricultural fields, can severely burn plant leaves when in contact with them or worse intoxicate the plants and kill them.
Oil spills present a similar danger. Oil is poisonous for most plant life, but it also blocks pores in soil and thus prevent aeration. Plant roots then lack access to oxygen.
Effects of noise pollution on plants
Modern life is noisy. There hasn’t ever been this much noise produced in the history of our planet than it has been in the past couple decades. With the population growth and resource extraction, world is only getting noisier even in remote locations. It makes sense to ask whether and how does this persistent increase in noise affect even plants.
Yes, it does. It may surprise some of us, while others would argue that it makes sense since plants are living organisms and are sensitive to changes in their environment. And noise creates vibrations after all.
Scientists from the California Polytechnic State University investigated how noise exposure affects plants in the long term, even when the noise has ceased already. They observed 75 percent less pine seedlings in noise affected area. Upon closer investigation of relationships in the ecosystem, scientists contribute this fact to absence of birds and pollinators in noisy environment . The presence of these little critters is important for trees, as they disperse their seeds over great stretches of land.
Everything in nature is interconnected. Pollution of all kinds can damage plant life and cause harm to the environment.
Once a plant has been weakened, it makes them more susceptible to disease and insect infestation.
This is also true for crops or other plants we rely on for food. Animals who eat polluted plants ingest these pollutants and have health problems. It is important to know that pollution causes a variety of damage to the planet as a whole.