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Image of Peter Crittenden
Associate Professor & Reader in Plant & Microbial Ecology, Faculty of Medicine & Health Sciences
BSc University of London (Westfield College) 1971; PhD University of Sheffield 1975; NERC/NATO Overseas Research Fellow, McMaster (Canada) 1975-77; Junior Research Fellow Research, Sheffield 1977-81; Lecturer, 1981 & Senior Lecturer, 2000, Nottingham; Visiting Scientist, Australian Antarctic Division 1995 and Antarctica new Zealand 2004/5; President, British Lichen Society 1998-99; President, International Association for Lichenology 2008-12; Senior Editor of 'The Lichenologist' 2000-current.
Lichens typically grow on surfaces that are deficient in available nitrogen and phosphorus such as rocks, tree bark and poorly developed soils. These habitats are universally distributed throughout… read more
Lichens typically grow on surfaces that are deficient in available nitrogen and phosphorus such as rocks, tree bark and poorly developed soils. These habitats are universally distributed throughout all terrestrial biomes but are particularly abundant at high latitudes. Atmospheric deposits, including rainfall, particulates and gases, are the principal sources of nitrogen and phosphorus for most lichens. Our work focuses on several key questions: what are the rates of nutrient supply to lichen surfaces; how efficiently do lichens capture nutrients from atmospheric supplies and are quantities captured by thalli sufficient for growth? We are also interested in how lichens might modify organic nutrients on their surfaces by means of surface bound enzymes and how nutrients move through the thallus to the photobiont cells; for example are all nutrients required by the photobionts supplied by the fungus?
15N-label being applied to Cladonia in heathland using a rainfall simulator.
Spruce-lichen woodland in northern Quebec.
Mat-forming lichens are one morphological group of lichens in which we are particularly interested. These are the reindeer lichens (e.g. Cladonia spp) and are of great ecological importance in Subarctic and Arctic regions, but they are also widespread and locally abundant in British heathlands.
Specific projects
Surface bound enzyme activities
Many lichens have a large capacity for phosphomonoesterase (PME) activity which is thought to promote the scavenging of phosphorus from atmospheric deposits. This enzyme is thought to be extracellular and its activity can be strongly up-regulated by N enrichment that might be caused by industrial N pollution or by ammonia released from animal colonies. We are now looking at different classes of phosphatases, including phytase, relationships between nitrogen fixation in cyanobacterial lichens, and at N-transforming enzymes such as urease. Our hypothesis is that suites of surface bound enzymes on lichen surfaces probably reflect the availability and forms of N and P in lichen habitats.
Nitrogen relationships in Cladonia portentosa in British heathlands(NERC).
Using 15N enrichment and 15N natural abundance methods we have tested the hypothesis that nitrogen is internally recycled in lichen thalli to support high growth rates. We believe that this mechanism might partly explain how Cladonia spp and other mat-forming lichens are able to dominate vegetation in heathlands.
Collecting Thyrea girardii from limestone cliffs near Barcelona.
Nitrogen fixation in lichenized unicellular cyanobacteria (European Science Foundation).
Many free-living unicellular cyanobacteria fix nitrogen during the night to avoid exposure of the functional nitrogenase to the damaging effects of oxygen produced in photosynthesis.
We have shown that symbiotic unicellular cyanobacteria in the lichen Thyrea girardii fix nitrogen during the day. We are currently investigating how this is achieved.
Impact of ammonia emissions from animal colonies (Leverhulme Trust, Royal Society, Antarctica New Zealand ).
Large animal colonies emit significant quantities of ammonia into the atmosphere derived from decomposition of excreta. We are investigating possible links between animal-derived ammonia emissions and the development of lichen communities at two locations: Cape Cross (seal colony, coastal Namib Desert ) and Cape Hallett (Adelie penguin rookery, Ross Sea , Antarctica ). Ammonia emitted at these sites is naturally enriched in 15N and this is being used to track the chemical and physiological impacts of ammonia deposition on lichen communities up to distances of 20-30km from the ammonia source. We are investigating the hypothesis that lichen communities might have developed in response to nutrient enrichment is being investigated.
The orange fruticose lichen Teloschstes capensis forms spectacular lichen 'fields' at Cape Cross , coastal Namib Desert.
Cape Hallett, Ross Sea area, Antarctica . Impacts on lichens of ammonia emissions from a major penguin rookery are being investigated.
Lichens as indicators of acid and nitrogen pollution.
Exposure to air pollution can modify the chemical composition of lichens. Mat-forming lichens (e.g. of the genus Cladonia) are particularly sensitive to deposition chemistry because they typically develop in open situations (e.g. heathlands) where incoming rainfall is little modified by plant (e.g. tree) canopies. We have found very strong relationships between the chemical composition of Cladonia portentosa and nitrogen and acid deposition across the British Isles . We have used Cladonia spp. as indicators of nitrogen deposition in the Russian Arctic in conjunction with other indicators, including the chemical composition of soil and winter snow pack (Eurpean Union, Framework V).
Assessing effects of industrial pollution on lichen diversity and chemical composition in the Russian tundra.
Sampling winter snow pack for chemical analysis in the Polar Ural Mountains, 60 km west of the industrial town of Vorkuta.
The ecology of lichen-dominated ecosystems
Many of the above studies are undertaken in habitats in which lichens are amongst the principal vegetation components. Our research results have implications for ecosystem function in these lichen-dominated communities.
Buellia frigida (an Antarctic endemic lichen) and Calplaca saxicola (a bipolar lichen species) are two species studied in a population genetics project.
Genetic variation in lichen-forming fungi (in collaboration with Dr Paul Dyer)
We have combined advances in the isolation and axenic culture of lichen-forming fungi and molecular biology techniques (e.g. DNA fingerprinting) to develop novel ways to explore sexual reproduction and population genetics of the fungal symbionts. This has led to studies of how sexual reproduction and physiology in lichens might be adapted to extreme environments in polar regions. We have sponsored the sequencing of the first lichen-forming fungal genome (Xanthoria parietina) currently being undertaken by the Joint Genome Institute in California.
Peter Crittenden is Senior Editor of the international journal The Lichenlogist (http://journals.cambridge.org/action/displayJournal?jid=LIC) and is President of the International Association for Lichenology (http://www.lichenology.org/).
University of Nottingham University Park Nottingham, NG7 2RD
telephone: +44 (0)115 9513300 (Undergraduate Enquiries) +44 (0)115 8230311 (Postgraduate Enquiries) fax: +44 (0)115 8230338 email: biology@nottingham.ac.uk
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