Can you begin by explaining the nature of lichens? Lichens are symbiotic associations between fungi, algae and/or cyanobacteria. Lichens do not have roots and they grow attached to the surfaces of rocks, trees and infertile soils such as peat or sand. They obtain nutrients from solutes in rainwater or dust in the air and are very efficient at scavenging nutrients from trace concentrations in the environment. They are therefore vulnerable to an enrichment of nutrient levels in the atmosphere. What prompted your interest in lichen biology? I became interested in lichens when at school in Manchester. I had already decided to study Botany at university by this point. Once, while walking in the Lake District I noticed the lush growth of lichens on trees, which was largely absent from trees in the Peak District near Manchester (where I usually walked). A friend told me that lichens were symbiotic associations and were composed of both a fungus and an alga and that they were sensitive to air pollution. Both of these concepts were new and fascinating to me. On subsequent walks in the Peak District I frequently searched for lichens, which were conspicuous by their absence. You established a project investigating phosphatase activity in lichens. What was the inspiration behind it? We examined lichen response to ammonia emitted from a major penguin rookery in the Antarctic. We hypothesised that lichens nearer to the rookery would respond to ammonia in the air by increased synthesis of a class of enzymes (phosphatases) which promote capture of phosphate (since extra nitrogen would upset the balance between nitrogen and phosphorus in the lichen). These enzymes are thought to be excreted and located in the fungal cell walls. Our hypothesis was correct, since phosphatase activity increased dramatically in lichens collected near to the rookery compared to those 13 km away. Close to the rookery the ammonia levels were toxic to most lichens but several species are tolerant of high ammonia concentrations; these were found to have low phosphatase activity. This was the first evidence that lichens tolerant of eutrophication had different physiological properties to those that were eutrophication sensitive. We then wondered whether the same physiological differences might be found in the British Isles between firstly, lichens in nitrogen- polluted regions and those in clean sites and, secondly, between lichens known to be sensitive to or tolerant of nitrogen pollution. All the differences we predicted were confirmed. Your project aims to have environmental and industrial applications. What do you envision these being? Nitrogen pollution is changing our environment. It primarily derives from oxides of nitrogen (NOx) emitted from combustion processes and ammonia (NH3) produced by farm livestock. In Europe, rainfall currently delivers about four times as much nitrogen as rainfall pre- Industrial Revolution. In 2000, it was estimated that in temperate regions nitrogen pollution is the primary driver of biodiversity loss, currently greater than climate warming, invasive species or land-use change. Lichens are especially useful as air pollution biomarkers because they derive their key nutrients, including nitrogen, from the atmosphere and respond strongly to contamination of air and rainwater. Different species of lichen respond to nitrogen enrichment in different ways. The past 10 to 15 years has seen a rapid increase in populations of a small number of lichen species that appear to be benefiting from nitrogen pollution. Other species continue to be rare or absent in agricultural and industrial regions and may be sensitive to the high rates of nitrogen deposition. The EU has set standards for concentrations of ammonia in the air, but measuring ammonia concentration is quite expensive in terms of both equipment and expertise. Several environmental agencies have therefore funded the development of a low-cost but quantitative lichen indicator scale for ammonia that could be used by agency staff. This uses lichens that appear to be either sensitive or resistant to ammonia pollution. Finally, where do you hope to see your research going in the future? My work will continue to focus on adaptions in lichens for growth in nutrient-poor environments and in understanding the functioning of lichen-dominated ecosystems. This work will include the response of lichens to nitrogen and phosphorus in the environment, principally the atmospheric environment. Professor Peter Crittenden has been fascinated with lichens since he was at school. Here, he discusses his recent research programme on lichens and how they may enable us to measure air pollution cheaply and effectively There’s lots to lichen Image courtesy of Harry Taylor (Natural History Museum) and OPAL. www.internationalinnovation.com 63 ECOLOGY
Transcript
Can you begin by explaining the nature of lichens?
Lichens are symbiotic associations between fungi, algae and/or cyanobacteria. Lichens do not have roots and they grow attached to the surfaces of rocks, trees and infertile soils such as peat or sand. They obtain nutrients from solutes in rainwater or dust in the air and are very efficient at scavenging nutrients from trace concentrations in the environment. They are therefore vulnerable to an enrichment of nutrient levels in the atmosphere.
What prompted your interest in lichen biology?
I became interested in lichens when at school in Manchester. I had already decided to study Botany at university by this point. Once, while walking in the Lake District I noticed the lush growth of lichens on trees, which was largely absent from trees in the Peak District near Manchester (where I usually walked). A friend told me that lichens were symbiotic associations and were composed of both a fungus and an alga and that they were sensitive to air pollution. Both of these concepts were new and fascinating to me. On subsequent walks in the Peak District I frequently searched for lichens, which were conspicuous by their absence.
You established a project investigating phosphatase activity in lichens. What was the inspiration behind it?
We examined lichen response to ammonia emitted from a major penguin rookery in the Antarctic. We hypothesised that lichens nearer
to the rookery would respond to ammonia in the air by increased synthesis of a class of enzymes (phosphatases) which promote capture of phosphate (since extra nitrogen would upset the balance between nitrogen and phosphorus in the lichen). These enzymes are thought to be excreted and located in the fungal cell walls.
Our hypothesis was correct, since phosphatase activity increased dramatically in lichens collected near to the rookery compared to those 13 km away. Close to the rookery the ammonia levels were toxic to most lichens but several species are tolerant of high ammonia concentrations; these were found to have low phosphatase activity. This was the first evidence that lichens tolerant of eutrophication had different physiological properties to those that were eutrophication sensitive.
We then wondered whether the same physiological differences might be found in the British Isles between firstly, lichens in nitrogen-polluted regions and those in clean sites and, secondly, between lichens known to be sensitive to or tolerant of nitrogen pollution. All the differences we predicted were confirmed.
Your project aims to have environmental and industrial applications. What do you envision these being?
Nitrogen pollution is changing our environment. It primarily derives from oxides of nitrogen (NOx) emitted from combustion processes and ammonia (NH3) produced by farm livestock. In Europe, rainfall currently delivers about four times as much nitrogen as rainfall pre-Industrial Revolution. In 2000, it was estimated that in temperate regions nitrogen pollution is
the primary driver of biodiversity loss, currently greater than climate warming, invasive species or land-use change.
Lichens are especially useful as air pollution biomarkers because they derive their key nutrients, including nitrogen, from the atmosphere and respond strongly to contamination of air and rainwater. Different species of lichen respond to nitrogen enrichment in different ways. The past 10 to 15 years has seen a rapid increase in populations of a small number of lichen species that appear to be benefiting from nitrogen pollution. Other species continue to be rare or absent in agricultural and industrial regions and may be sensitive to the high rates of nitrogen deposition.
The EU has set standards for concentrations of ammonia in the air, but measuring ammonia concentration is quite expensive in terms of both equipment and expertise. Several environmental agencies have therefore funded the development of a low-cost but quantitative lichen indicator scale for ammonia that could be used by agency staff. This uses lichens that appear to be either sensitive or resistant to ammonia pollution.
Finally, where do you hope to see your research going in the future?
My work will continue to focus on adaptions in lichens for growth in nutrient-poor environments and in understanding the functioning of lichen-dominated ecosystems. This work will include the response of lichens to nitrogen and phosphorus in the environment, principally the atmospheric environment.
Professor Peter Crittenden has been fascinated with lichens since he was at school. Here, he discusses his recent research programme on lichens and how they may enable us to measure air pollution cheaply and effectively
There’s lots to lichen
Image courtesy of Harry Taylor (Natural History Museum) and OPAL.
www.internationalinnovation.com 63
ECOLOGY
LICHENS ARE SOME of the most remarkable organisms on Earth. There are approximately 20,000 species worldwide and every one of them is composed of two or more living things, where fungi, algae and/or cyanobacteria come together to form a symbiotic relationship of benefit to all parties. What is perhaps more fascinating is that the interaction results in the formation of structures that none of their components possess when grown separately; they are literally more than the sum of their parts.
Lichens are extremely hardy, growing on surfaces containing few nutrients and experience frequent desiccation such as rocks, tree bark and poorly developed soils. These occur in most terrestrial environments, from tropical rainforests and deserts to high mountain tops and arctic tundra. Lichens have no roots and obtain water and nutrients from rainwater and dust in the atmosphere. They are capable of living on both natural and manmade surfaces and have been found growing on glass, bones and even on the back of beetles. Some lichen species do not grow attached to anything at all and lichen tumbleweed spend their existence on the wind’s hand, while others have been taken into
space by scientists and brought back to Earth with no discernible effect.
ECOLOGICAL IMPORTANCENitrogen is the most abundant element in the Earth’s atmosphere and is essential for life. However, unless nitrogen gas is converted to nitrogen salts, the majority of organisms cannot make use of it. Fortunately, lichens (specifically those containing cyanobacteria) are able to ‘fix’ the nitrogen gas and release it into the soil. Lichens are among the principal agents of nitrogen fixation in the Arctic where they also provide an important foodstuff for caribou and reindeer. Their extensive ground coverage in cold regions additionally promotes water conservation, and in arid lands lichens are components of soil crust communities that help to maintain soil stability.
Lichens have long been known to be useful as air pollution indicators. As far back as 1866, William Nylander observed that lichens were extremely sensitive to pollution in the air and the
number of lichens of different species in any given area was an effective means of testing the quality of the air (where the greater the abundance of lichens and species diversity, the better or ‘cleaner’ the air was). This sensitivity to pollution continues to interest scientists today, including a team of researchers at The University of Nottingham who are investigating the ways in which lichens are adapted to
Researchers at The University of Nottingham are investigating how lichens are adapted to their extreme habitats in the hope that it will lead to industrial applications and provide an effective means of monitoring nitrogen pollution in the environment
Looking at lichens
The common orange lichen, Xantheria parietina, grows in nutrient enriched sites. X. parietina was the first lichen fungus for which the entire genome sequence was determined, a project sponsored by the team at The University of Nottingham.
Hypogymnia physodes, a nitrogen-sensitive lichen species. Image courtesy of Harry Taylor (Natural History Museum) and OPAL.
64 INTERNATIONAL INNOVATION
ECOLOGICAL SIGNIFICANCE OF SURFACE BOUND ENZYME ACTIVITIES IN LICHENS
OBJECTIVES• To study the response of lichens to changes in
environment, particularly air quality
• To understand how lichens are adapted to survive in extreme environments and ecosystems
KEY COLLABORATORSDr Niall F Higgins, The University of Nottingham, UK
Gabrielle Brown, The University of Nottingham, UK
Centre for Ecology & Hydrology, Edinburgh, UK
Natural History Museum, London, UK
FUNDINGNatural Environment Research Council (NERC)
CONTACTProfessor Peter Crittenden
Room B79 Biology Building University Park Nottingham NG7 2RD UK
PETER CRITTENDEN received his BSc from the University of London before completing his PhD at the University of Sheffield, UK, in 1975.
He has since held multiple positions, including at McMaster University, Canada, and the University of Sheffield. He is currently a Professor in the School of Life Sciences at The University of Nottingham as well as a Senior Editor of The Lichenologist. He has previously served as President of the British Lichen Society 1998-99 and the International Association for Lichenology 2008-12.
different levels of nitrogen in the environment to ensure their survival. It is hoped that increasing understanding of lichens and their adaptive processes could have both a commercial and environmental impact.
PHYTE OR PHOBE?The team, led by Professor Peter Crittenden, has demonstrated that lichens are able to produce enzymes on their surfaces that enable them to maximise their intake of nutrients in rain water. However, different lichen species respond differently to increased availabilities of nitrogen and phosphorus in the air but the reasons for this are not yet fully understood. By focusing on the surface enzyme activities, the team has discovered differences between nitrophytes (nitrogen tolerant or loving) and nitrophobes (nitrogen intolerant or hating): “Nitrophobes have high activities of enzymes that promote scavenging of phosphorus but low activities of enzymes that promote scavenging of nitrogen, while the reverse situation pertains for nitrophytes,” explains Crittenden. These enzymes, known as phosphatases and peptidases, respectively, enable lichens to make use of nutrients that would otherwise be unavailable. Interestingly, lichens have been shown to increase phosphatase activity when moved from unpolluted areas to ones where the level of nitrogen is higher, while the opposite is true of those moved from nitrogen-enriched areas to ‘cleaner’ environments.
LOCATING PHOSPHATASESThe researchers employed imaging technologies to determine where the
phosphatase activity in lichens was located and to better understand the function of the enzymes. By using a fluorescent stain they found the enzyme activity was located mainly in cells at the surface of the thallus (the vegetative part of the lichen). This would be an advantageous position for these surface-bound enzymes in order for them to break down nutrients deposited on the lichen.
One of these classes of enzymes, known as phytases, is produced industrially around the world as an additive to animal feed. In learning more about the specifics regarding phytase production, the team and collaborators might be able to stimulate the production of novel phytases, which will be of significant benefit to manufacturers and farmers. That phytases have the additional effect of reducing the amount of phosphate in animal waste is beneficial to the environment, as it is phosphate loads that can cause eutrophication of water bodies.
LICHEN SCALESEnvironmental agencies currently employ lichen scales to measure nitrogen pollution in the air. In the OPAL project, citizen scientists are encouraged to conduct an Air Survey utilising lichens found on trees to indicate levels of nitrogen pollution and report their findings online. With Crittenden and his team’s research, it is hoped that biomarkers with a faster response time to nitrogen changes can be developed. That nitrogen pollution is the leading cause of biodiversity loss in north temperate regions only heightens the importance of the team’s investigations.
PARTICIPATE IN THE OPAL AIR SURVEY The Open Air Laboratories (OPAL) network is a UK-wide community science initiative that encourages the public to get involved with nature. Their OPAL Air Survey aims to find out more about air quality in the UK by studying lichens – it urges the public to get involved.
Visit http://bit.ly/OEN_airsurvey to find out more.
LICHENS AND NITROGEN AIR QUALITY Download an app and field guide for monitoring local air quality at http://bit.ly/lichenguide
