Greta Jimenez
Lichens are composite organisms that are the result of a symbiotic relationship between a fungus and an alga or cyanobacteria. They are found in a variety of environments, from rocky mountainsides to human-made structures like concrete. Lichens are sensitive to air pollution because they absorb their nutrients directly from the atmosphere, making them valuable as indicator species. While lichens are typically associated with the colour green, they can also be yellow, orange, red, black, brown, silver, or grey. The presence of different colours of lichens can indicate the level of pollution in an environment, with certain species only being able to grow in areas with low levels of pollution. For example, the presence of Usnea lichens, also called old man's beard, indicates that there is no sulphur dioxide pollution in the area.
| Characteristics | Values |
|---|---|
| Colour change due to pollution | Lichens turn pink, then bleach, and finally turn green before dying |
| Type of pollution | Nitrogen, sulphur dioxide, ammonia, heavy metals, photo-oxidants, and other acidic pollutant gases |
| Tolerance | Some lichens are more tolerant of pollution than others |
| Indicator species | Lichens are used as indicators of air quality and pollution levels |
| Distribution | The variety and number of lichens in an area indicate the level of pollution |
| Sensitivity | Lichens are very sensitive to atmospheric changes, especially in moist conditions and during temperature changes |
| Human uses | Lichens are used as a source of potential antibiotics, anti-fungal and anti-cancer drugs, perfumes, incense, and clothes dye |
| Habitat | Lichens are found in nature and human-made environments, including rocks, trees, barren earth, metal, and concrete |
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What You'll Learn
Lichens are useful indicators of air quality
Lichens are composite organisms that result from a symbiotic relationship between a fungus and a photosynthetic partner, typically algae or cyanobacteria. The fungus forms a protective outer cover for the enclosed algae, absorbing water and nutrients from the air, while the photosynthetic partner generates organic compounds through photosynthesis. This enables lichens to flourish in diverse environments, from rocky mountainsides to harsh Arctic tundras.
The presence or absence of certain lichen species can indicate typical sulphur dioxide levels in an area. For instance, the absence of lichens indicates very poor air quality, while crusty lichens like Lecanora conizaeoides or Lepraria incana can tolerate poor air quality. In moderate to good air, leafy lichens like Parmelia caperata or Evernia prunastri can survive, and in areas with very clean air, rare species like Usnea articulata or Teloschistes flavicans may grow.
Lichen studies have been used to assess air pollution in certain European countries and as indicators of nitrogen pollution from tea estates in Sri Lanka and the forests of the Himalayas. Lichens were also used to detect mercury poisoning near a thermometer manufacturing factory in Kodaikanal, India.
However, it is important to note that not all lichens are sensitive to air pollution, and some crustier lichens are more tolerant than hairy lichens. Lichens are also limited in that they can only monitor nitrogen and sulphur dioxide levels, while there are numerous other pollutants that pose ecological and health threats.
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Nitrogen and sulphur dioxide are the two pollutants that most affect lichens
Lichens are composite organisms that result from a mutualistic alliance between a fungus and a photosynthetic partner, typically algae or cyanobacteria. They are highly sensitive to changes in their environment, which makes them excellent indicators of air quality.
Sulphur dioxide is another pollutant that has killed many lichens. It can irritate the mucus lining of the eyes, nose, throat, and lungs, causing coughing and tightness in the chest. Usnea lichens, also called old man's beard, do not grow in areas with sulphur dioxide pollution. Sulphur dioxide also interferes with cyanobacteria's ability to fix nitrogen, which is necessary for lichens to produce proteins and organic acids. It also destroys the chlorophyll of the alga, inhibiting photosynthesis and impeding lichen reproduction.
The presence and health of lichens can be used to monitor nitrogen and sulphur dioxide pollution levels in an area. Different lichen species have different sensitivities to these pollutants, so the variety of lichen species must be taken into account when calculating the air quality index. For example, "nitrophyte" lichen species thrive in high-nitrogen environments, while "acidophyte" species prefer low-nitrogen environments. Similarly, the presence of certain lichen species on tree bark can indicate typical sulphur dioxide levels in the area.
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Lichens are sensitive to atmospheric changes
Lichens are used as bioindicators of atmospheric pollution. Their presence or absence can indicate the level of air pollution in an area. For example, if there are no lichens present, the air quality is very poor. In areas of moderate to good air quality, leafy lichens such as Parmelia caperata or Evernia prunastri can survive. In very clean air, rare species such as Usnea articulata or Teloschistes flavicans may grow. Lichens are particularly sensitive to nitrogen and sulphur dioxide pollution. Nitrogen dioxide in the air can be a powerful pollutant and become harmful to human health in high concentrations. Sulphur dioxide pollution can irritate the mucus lining of the eyes, nose, throat, and lungs and cause coughing and tightness in the chest.
The sensitivity of lichens to atmospheric nitrogen has been studied in the UK, where nitrogenous pollutants have impacted the lichen flora of oak and birch trees. In the Netherlands, high levels of ammonia have led to the disappearance of acid-preferring lichen species. Lichens are also being used to study the effects of nitrogen pollution from tea estates in Sri Lanka and the forests of the Himalayas.
Not all lichens are sensitive to air pollution. Crustier lichens tend to be hardier than hairy lichens, and some species are more tolerant of nitrogen. For example, the golden shield lichen (Xanthoria parietina) can live in areas with high levels of nitrogen, especially ammonia. Some species of lichen have become more widely distributed than they were a century ago, as they are more tolerant of acid conditions associated with SO2 deposition.
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Lichens can indicate typical sulphur dioxide levels
Lichens are excellent bioindicators of sulphur dioxide levels in the lower troposphere. They are sensitive to atmospheric pollution, including sulphur dioxide, which comes from coal burning and industrial processes. Sulphur dioxide dissolves in water to produce acidic ions, which are readily absorbed through the lichen thalli, further disrupting their ability to photosynthesize. The presence of sulphur dioxide in the atmosphere can be determined by studying lichens.
Lichens are composite organisms resulting from a mutualistic alliance between a fungus and a photosynthetic partner, typically algae or cyanobacteria. The fungus forms a protective outer cover for the enclosed algae. While the fungus absorbs water and nutrients from the air, the photosynthetic partner generates organic compounds through photosynthesis. This harmonious partnership enables lichens to flourish in diverse environments, ranging from rocky mountain sides to harsh Arctic tundras.
Lichens get their nutrients from the air. Because they have no roots or protective surface, they cannot filter what they absorb, so anything in the air is taken straight inside. If there are pollutants, it can accumulate in the lichen and can become toxic very quickly. Lichens make great air pollution indicators because they are very sensitive and respond to pollution in short time frames.
The presence or absence of lichens can indicate air quality. The diversity and health of lichen species in an area can provide information about the levels of pollution. Some lichen species are more tolerant of pollution, while others are more sensitive. Scientists monitor lichen communities to detect changes in species composition and health, which can signal potential ecosystem decline due to pollution.
The two main air pollutants that affect lichen growth are nitrogen and sulphur dioxide. Nitrogen dioxide is formed when nitrogen is heated and combined with oxygen, such as in car engines. It is a powerful pollutant that can harm human health by irritating the lungs and causing respiratory issues. Sulphur dioxide is produced by coal burning and industrial processes. While sulphur dioxide levels have decreased in some regions due to reduced coal usage, it still affects lichens and can irritate the mucous membranes of humans, causing coughing and chest tightness.
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Lichens are used to study air pollution in some European countries
Lichens are composite organisms that are the result of a symbiotic relationship between a fungus and an algae or cyanobacteria. The fungus forms a protective outer cover for the algae or cyanobacteria, which generates organic compounds through photosynthesis. This partnership allows lichens to grow in a variety of environments, from rocky mountainsides to Arctic tundras.
Lichens are sensitive to air pollution and can act as bioindicators of air quality and climate change. They are particularly susceptible to pollutants due to their lack of roots and protective cuticles, which means they cannot filter what they absorb from the air. As the pollution load in the air rises, the lichen cell breaks, leading to the bleaching and eventual death of the organism. Lichens have been used as indicators of sulphur dioxide (SO2) concentration since the 1970s. More recently, studies have shown a correlation between lichens and nitrogen oxides (NOx) and reduced nitrogenous pollutants such as ammonia (NH3). Lichens that grow on trees (epiphytic lichens) have been widely studied in relation to these pollutants.
In certain European countries, lichen studies are included in policy documents to study air pollution. For example, in the UK, the lichen flora of oak trees in agricultural areas has changed from communities dominated by species preferring acidic bark to species that tolerate and benefit from nitrogen. In the Netherlands, high levels of ammonia have led to the disappearance of acid-preferring species and the dominance of nitrophytic species. Studies in Germany have examined the occurrence of lichens in relation to various environmental factors and assessed the changes in lichen flora in response to altered air pollution and climate change.
Overall, the presence and abundance of lichens can provide valuable information about local air quality and the effects of air pollution on ecosystems.
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Frequently asked questions
Lichens do not change color when exposed to pollution. Instead, they either stop growing or die.
Lichens do not change color when exposed to nitrogen. However, they can bleach and eventually die.
Nitrogen-tolerant lichens, also known as "nitrophyte" lichens, do not change color. They are characterized by their ability to thrive in high-nitrogen environments.
Lichens do not change color when exposed to sulfur dioxide. However, they may stop growing in areas with high levels of this pollutant.
