Lichen's Superpower: Fighting Air Pollution

Lichens are composite organisms that combine fungi and algae or cyanobacteria. They are durable, growing on tree bark and bare rock, yet are sensitive to air pollution and air quality. This makes them excellent bio-indicators of air quality. Scientists can monitor lichen communities to determine the sources and levels of pollution. Lichens are sensitive to a range of pollutants, including sulphur, nitrogen, acidity, halogens, heavy metals, and ozone. They can indicate the presence of dangerous pollutants like lead and respond to changes in pollution levels in short time frames. Lichens can also help us understand the effects of air pollution on ecosystems and the communities that rely on them.

Lichens are sensitive to air pollution and can indicate air quality

Lichens are therefore excellent bio-indicators of air quality. They are like an early warning 'canary' for chemically sensitive vascular plants. Scientists can monitor the health of lichens and pair this data with atmospheric deposition data to determine the sources and levels of 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.

The presence or absence of lichens can indicate the air quality of an environment. In places with poor air quality, generally only crusty lichens can survive. In moderate to good air quality, leafy lichens can survive, and in areas with very clean air, rare species may grow. The size and variety of lichens in an area can also indicate the level of pollution—as a rule of thumb, the smaller the size and the less variety of lichens in an area, the more polluted the environment.

Lichens are also sensitive to different types of pollutants. Some lichens are more sensitive to sulphur, nitrogen, acidity, halogens (e.g. fluoride), heavy metals, or ozone. For example, the Usnea lichen does not grow in areas where there is sulphur dioxide pollution. Certain species of lichen are also more tolerant of nitrogen than others.

Overall, lichens are useful indicators of air quality and can provide valuable information on atmospheric pollution.

They absorb nutrients and pollutants from the air, through rain and dust

Lichens are composite organisms, made up of a fungus and an algae or cyanobacteria. They are durable, able to grow on tree bark and bare rock, but they are also sensitive to air pollution and air quality. This is because they have no roots or protective surface, so they absorb everything from their environment.

Lichens absorb nutrients and pollutants from the air, through rain and dust. They are like sponges, with their entire thallus exposed to their surrounding environment. The rainwater supply and the absorption of air, essential for gas exchanges for photosynthesis and respiration, are done by the entire thallus. The mucilages of the walls absorb water, and the dust is trapped. Lichens get their nutrients from the air, and because they cannot filter what they absorb, pollutants can accumulate and become toxic.

Lichens are sensitive to a range of pollutants, including sulphur, nitrogen, acidity, halogens (such as fluoride), heavy metals, and ozone. They are also affected by the pH of their environment. For example, ammonia deposition can cause the pH of tree bark to increase, which has been linked to the disappearance of certain lichen species.

The presence or absence of certain lichen species can indicate the level of air pollution in an area. For example, in areas with poor air quality, only crusty lichens may be present, while in moderate to good air quality, leafy lichens may be found. In very clean air, rare species may grow. Scientists can monitor lichen communities to determine the sources and levels of pollution.

They are used to monitor the health of ecosystems and the effects of pollution

Lichens are used as bio-indicators of air quality and can provide information on atmospheric pollution. They are sensitive to air pollution and can act as signals that the air is safer to breathe. They are also used to monitor the health of ecosystems and the effects of pollution.

Lichens are composite organisms that combine fungi and algae or cyanobacteria. They are generally subtle and unnoticed, found on the ground, tree trunks, or rocks. Lichens do not have any roots or protective physical structures, so they absorb anything in the air straight inside. If there are pollutants, they can accumulate in the lichen and become toxic. Scientists who monitor the health of lichens can pair this bio-monitoring data with atmospheric deposition data to determine the sources and levels of pollution causing detrimental effects.

Lichens are used to monitor the health of ecosystems by indicating the typical levels of pollutants such as SO2. For example, if there are no lichens present, the air quality is very poor. Only crusty lichens, such as Lecanora conizaeoides or Lepraria incana, can tolerate poor air quality in terms of SO2. In moderate to good air, leafy lichens such as Parmelia caperata or Evernia prunastri can survive. In areas where the air is very clean, rare species such as Usnea articulata or Teloschistes flavicans may grow.

In addition, lichens are used to study the effects of nitrogen air pollution. For example, researchers in Sri Lanka are setting up permanent plots in mountain cloud forests to record how the lichen community changes over time in response to different nitrogen concentrations. This research will help understand how increases in fertiliser use on tea farms will change the ecology of southern Asia.

Lichens are also used to track levels of airborne pollutants over long periods. For example, one species was used to track lead levels over a 100-year period, and another species, Stereocaulon pileatum, has been found to favour metal-enriched substrata and has spread in areas with lead pollution.

Lichens can indicate the typical sulphur dioxide levels in an area

Lichens are miniature ecosystems that are the result of a symbiotic relationship between fungus and algae and/or cyanobacteria. They are durable, able to grow on tree bark and bare rock, yet sensitive to air pollution and air quality. This makes them excellent bio-indicators of air pollution.

Lichens absorb nutrients, water, and pollutants from the air through rain and dust. Sulphur dioxide, a pollutant that comes from coal-burning and industry, has killed many lichens in the UK in the past. However, since coal burning has reduced, sulphur dioxide levels have decreased, and lichens are beginning to return.

Usnea lichens, also called old man's beard, do not grow in areas where there is sulphur dioxide pollution. The presence of these lichens indicates that coal has not been burnt in the area for some time. Conversely, the golden shield lichen (Xanthoria parietina) can live in areas with high levels of nitrogen, especially ammonia. They are common on trees and buildings near farmland and on sea cliffs where seabirds' droppings provide nitrogen.

Scientists can monitor the health of lichens and pair this data with atmospheric deposition data to determine the sources and levels of pollution. Lichens can therefore indicate typical sulphur dioxide levels in an area, and their presence or absence can give an indication of the sulphur dioxide levels in the past.

They are used as bio-indicators of nitrogen pollution

Lichens are sensitive to atmospheric pollution, including nitrogen (N), because they absorb all their nutrients and water from the air through wet and dry deposition. Nitrogen deposition can increase the load of nutrients, and too much nitrogen can harm and kill the algae's chlorophyll, which is used to produce sugars that feed the lichen.

Some lichens will die in the presence of nitrogen, while others will thrive. For example, the golden shield lichen (Xanthoria parietina) can live in areas with high levels of nitrogen, especially ammonia. It is commonly found on trees and buildings near farmland and on sea cliffs where seabird droppings provide nitrogen.

Scientists monitor lichen communities to determine the sources and levels of pollution causing detrimental effects. If they observe an increase in nitrogen-tolerant species, along with a decrease in nitrogen-sensitive species, it may indicate an increase in atmospheric nitrogen deposition. This shift in species composition and their health can signal the potential beginning of ecosystem decline due to nitrogen deposition.

In Sri Lanka, researchers are using lichens as indicators to monitor the effects of nitrogen air pollution. They have set up permanent plots in the mountain cloud forests and are recording how the lichen community in these plots changes over time. This research will help them understand how increased fertiliser use on tea farms will impact the ecology of southern Asia.

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