Lichen's Resilience: Air Pollution's Impact Explored

Lichens are composite organisms that combine fungi and algae or cyanobacteria. They are sensitive to air pollution because they absorb nutrients directly from the atmosphere through their surface. This makes them valuable bioindicators of air quality. Lichens are affected by various air pollutants, with nitrogen and sulphur dioxide being the most impactful. Nitrogen deposition can harm and kill the algae's chlorophyll, which is essential for producing sugars that feed the lichen. Sulphur dioxide, on the other hand, interferes with the cyanobacteria's ability to fix nitrogen and also destroys the chlorophyll, inhibiting photosynthesis. The presence or absence of certain lichen species in an area can indicate the level of air pollution, with some species being more tolerant of pollutants than others.

Lichens absorb nutrients from the air, so they cannot filter pollutants

Lichens are composite organisms that combine fungi and algae or cyanobacteria. They are found in nature and in human-made environments, including rocks, trees, barren earth, metal and concrete. They are sensitive to air pollution because they absorb nutrients directly from the atmosphere. This makes them valuable as indicator species.

Lichens do not have roots or a protective surface, so they cannot filter what they absorb. If there are pollutants in the air, they are taken straight into the lichen and can quickly become toxic. Lichens are highly susceptible to changes in atmospheric chemistry and deposition and, for this reason, provide very sensitive indicators of such changes. They are the "canaries in the coal mine" of nitrogen deposition.

The two main air pollutants that affect lichen growth are nitrogen and sulphur dioxide. Lichens need nitrogen to survive as it helps them produce necessary proteins and organic acids. Certain lichen species are sensitive to ammonia, which is a more stable and easier-to-use form of nitrogen. Too much nitrogen can over-fertilise certain lichen species and cause them to die. Excess nitrogen can also kill the chlorophyll of the alga, which deprives the fungi of the necessary sugars for survival.

Lichens are also sensitive to sulphur dioxide, which easily dissolves in water and is prevalent in the air in its gaseous state. Sulphur dioxide interferes with the cyanobacteria's ability to fix nitrogen and destroys the chlorophyll of the alga, thus inhibiting photosynthesis. The compound also impedes lichen reproduction and spore germination across certain species.

Different lichen species have different sensitivities to air pollutants. The shrubby and leafy varieties are the most sensitive, while the crustose lichens that grow like a crust on a surface are the most tolerant.

Sulphur dioxide and nitrogen are the main air pollutants that affect lichens

Nitrogen is a harmless gas and makes up a large part of the Earth's atmosphere. However, when heated and combined with oxygen, as it is in a car engine, nitrogen oxides are created. Nitrogen dioxide is a powerful air pollutant and is harmful to human health in high concentrations. In UK cities, around half of the nitrogen dioxide air pollution comes from road traffic. Farms also emit nitrogen pollutants from fertilizers, farm machinery, and livestock waste. Nitrogen dioxide can inflame the lining of the lungs and cause respiratory issues such as shortness of breath and coughing. It can also decrease the body's immune response to lung infections and cause more frequent asthma attacks.

Some lichens will die in the presence of nitrogen, while others will thrive. Crustier lichens tend to be hardier than hairy lichens. The golden shield lichen, for example, can live in areas with high levels of nitrogen, especially ammonia. It is often found on trees and buildings near farmland.

Sulphur dioxide is another pollutant that affects lichens. This comes from coal burning and industry. Sulphur dioxide has killed many lichens in the UK in the past, but, as we now burn less coal, lichen populations are beginning to recover. In high concentrations, sulphur dioxide can irritate the mucus lining of the eyes, nose, throat, and lungs. It may cause coughing and tightness in the chest. People with asthma are particularly sensitive to sulphur dioxide pollution.

Usnea lichens, also called old man's beard, do not grow in areas with sulphur dioxide pollution. If you see one of these lichens, it probably means that coal has not been burnt in the area for some time.

Sulphur dioxide interferes with cyanobacteria's ability to fix nitrogen

Sulphur dioxide is a pollutant that is released into the atmosphere through coal burning and industrial activity. Sulphur dioxide is particularly harmful to cyanobacteria, which are a type of bacteria that can fix nitrogen from the atmosphere. Nitrogen fixation is the process by which nitrogen in the atmosphere is converted into ammonia, nitrates, and nitrites, which can then be used by plants and converted into proteins.

Sulphur dioxide interferes with the ability of cyanobacteria to fix nitrogen by inhibiting the activity of the nitrogenase enzyme, which is responsible for converting nitrogen into ammonia. This interference occurs because sulphur dioxide affects the electron transport chain that provides the reductants necessary for nitrogen fixation and assimilation. Sulphur dioxide also disrupts the synthesis of the nitrogenase enzyme, as it requires specific trace elements, such as iron and molybdenum, which can be limited by the presence of sulphur dioxide.

The inhibition of nitrogenase activity and synthesis by sulphur dioxide leads to a decrease in the amount of fixed nitrogen available to plants, which can have negative impacts on ecosystems and agricultural systems that rely on nitrogen fixation for nutrient cycling and plant growth.

To mitigate the effects of sulphur dioxide pollution on nitrogen fixation by cyanobacteria, it is important to reduce emissions of sulphur dioxide into the atmosphere through the implementation of pollution control measures and the use of cleaner technologies in industrial processes. Additionally, the development of sulphur dioxide-tolerant strains of cyanobacteria through genetic engineering or the selection of naturally occurring tolerant strains can help improve nitrogen fixation in areas with high levels of sulphur dioxide pollution.

Nitrogen dioxide can be a powerful pollutant and is harmful to human health

Lichens are highly sensitive to changes in atmospheric chemistry and deposition, and as such, they are excellent indicators of air quality. They are miniature ecosystems made of fungus and algae and/or cyanobacteria. The algae or cyanobacteria provide the fungus with sugars made from sunlight, and the fungus provides a home. Lichens absorb nutrients from the air, and due to the lack of a protective surface, they cannot filter what they absorb, making them susceptible to pollutants.

Nitrogen dioxide (NO2) is a powerful air pollutant and a member of the nitrogen oxides (NOx) group of highly reactive gases. It is primarily produced by burning fossil fuels such as coal, oil, methane gas, and diesel at high temperatures. NO2 emissions also come from vehicles, power plants, industrial processes, and agricultural activities.

Nitrogen dioxide can have detrimental effects on human health, especially when exposed to high concentrations. It can irritate and inflame the lining of the lungs, causing respiratory issues such as coughing, wheezing, and shortness of breath. Prolonged exposure may contribute to the development of asthma and increased susceptibility to lung infections. Vulnerable groups, including children, the elderly, pregnant individuals, and those with pre-existing respiratory conditions, are at an even higher risk of adverse health effects.

The impact of NO2 on human health is significant, and it is crucial to monitor and reduce emissions to protect vulnerable populations and improve overall air quality. Lichens play a crucial role in indicating the presence of NO2 and other air pollutants, helping to identify areas of concern and guide efforts to mitigate air pollution.

Lichens are sensitive to air pollution and act as bioindicators

Lichens are often described as the "canaries in the coal mine" of nitrogen deposition. They are used as bioindicators because they are sensitive to a number of air pollutants, including sulphur dioxide, nitrogen, acidity, halogens, heavy metals, and photo-oxidants. Sulphur dioxide, for example, interferes with the cyanobacteria's ability to fix nitrogen and destroys the chlorophyll of the algae, inhibiting photosynthesis.

The presence or absence of lichens, as well as the variety of lichen species in a given area, can indicate the level of air pollution. If there are no lichens present, the air quality is very poor. Crustose lichens, which grow closely adhered to substrates like tree bark or stone, can tolerate poor air quality. Leafy lichens indicate moderate to good air quality, while rare species like Usnea articulata or Teloschistes flavicans may grow in areas with very clean air.

The health of lichen species is monitored and paired with atmospheric deposition data to identify sources and levels of pollution. This process has been used in the United States and Germany to protect sensitive ecological systems. Lichens are also being used to monitor nitrogen levels at tea farms in Sri Lanka and the Himalayan forests.

Lichens are valuable bioindicators because they are found in a variety of environments, including natural settings like rocks, trees, and barren earth, as well as human-made environments like metal and concrete. They are also easy to study and quick to respond to environmental changes.

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