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dc.contributor.authorCrittenden, Peter D.
dc.contributor.authorThornton, Barry
dc.contributor.authorWanek, Wolfgang
dc.coverage.spatialScotland, England and Wales, Sweden, Finland & Russiaen_UK
dc.description.abstract1. The circumboreal/circumpolar N2-fixing lichen Stereocaulon vesuvianum is amongst the most widespread and abundant fruticose species in montane Britain but has lost the capacity to fix N2 over large areas of the country. 2. To investigate whether loss of N2-fixation in S. vesuvianum is linked to increased N deposition, we examined thallus morphology, physiology and chemistry at twelve locations representing an N deposition gradient of 3-40 kg ha-1 yr-1. Measurements were made in parallel on a non-N2-fixing reference species (Parmelia saxatilis). Presence or absence of cephalodia (N2-fixing nodules containing the cyanobacterium Stigonema sp) was recorded in over 500 herbarium specimens of S. vesuvianum dating back to 1820. 3. Cephalodium abundance in S. vesuvianum, and 15N concentration in S. vesuvianum and P. saxatilis, were strongly negatively correlated with N deposition and particularly with dry deposited N; cephalodia do not form at total N deposition rates ≥ 8-9 kg ha-1 yr-1. Other morphological oddities in S. vesuvianum at N-polluted sites include increased apothecium (fungal reproductive structure) production and green algal biofilm development. Biofilm covered thalli without cephalodia lacked nitrogenase activity and cephalodia at sites where they rarely develop had nitrogenase activities typical for this species. The presence or absence of cephalodia in herbarium specimens of S. vesuvianum suggest that the present-day N-deposition linked gradient in N2-fixing capacity did not exist in the 19th century and largely developed between 1900-1940. 4. Synthesis. We provide clear evidence that N2-fixing capacity in S. vesuvianum has been lost in regions subjected to many decades of enhanced atmospheric N deposition. This loss is consistent with established models of diazotrophy which identify supply of combined N as an inhibitor of N2-fixation. Progressive depletion of thallus 15N with increasing N deposition is in line with available data suggesting that much atmospheric N pollution is 15N-depleted. Rates of nitrogenase activity in S. vesuvianum are low compared to other symbiotic systems and perhaps more likely supplanted by elevated N deposition. We suggest that other ecosystem compartments with low rates of fixation (e.g. soils) might also be susceptible to N pollution and merit investigation.en_UK
dc.publisherThe University of Nottinghamen_UK
dc.subject.lcshNitrogen -- Fixationen_UK
dc.subject.lcshNitrogen compounds -- Environmental aspectsen_UK
dc.titleData from: Loss of nitrogen fixing capacity in a montane lichen is linked to increased nitrogen depositionen_UK
dc.subject.freecephalodia, herbarium specimens, lichens, 15N natural abundance, nitrogen deposition, nitrogen fixation, Stereocaulon vesuvianumen_UK
dc.subject.jacsBiological Sciencesen_UK
dc.subject.lcQ Science::QK Botanyen_UK
uon.divisionUniversity of Nottingham, UK Campus::Faculty of Medicine and Health Sciences::School of Life Sciencesen_UK
uon.datatypeRaw data underlying values in graphsen_UK
uon.funder.freeLeverhulme Trusten_UK
uon.collectionmethodLaboratory observations and chemical analysesen_UK
uon.rightscontactP.D. Crittendenen_UK

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