title: The nitrogen fixation potential of arctic cryptogram species is influenced by enhanced UV-B radiation.
abstract: Effects of enhanced UV-B (representing a 15% ozone depletion) on cyanobacterial nitrogen fixation were measured at a high arctic site (Adventdalen, 79°N, Svalbard) and a subarctic site (Abisko, 68°N, Sweden). Nitrogen fixation potential (acetylene reduction) by cyanobacteria associated with the moss Sanionia uncinata in vegetation exposed to experimentally enhanced levels of UV-B for 3 and 4 years in the high arctic in Adventdalen was reduced by 50% compared to controls after 3 years. No reduction in nitrogen fixation potential was observed in cyanobacteria associated with the moss Hylocomium splendens when previously exposed to enhanced UV-B in Abisko for a 7-year period. However, in the same experiment a 50% increase in summer precipitation stimulated nitrogen fixation potential by up to 6-fold above the natural precipitation treatments both in cyanobacteria associated with vegetation exposed to natural and enhanced UV-B radiation. In contrast to the lack of UV effect on moss-associated nitrogen fixation at the subarctic site, nitrogen fixation potential by the dominant lichen species Peltigera aphthosa was reduced by 50% when measured after 8 years exposure to elevated UV-B treatment. Evidence from these studies highlights the importance of UV-B radiation for cyanobacterial nitrogen fixation in the Arctic and future impact on nitrogen availability in such plant communities.
authors.affiliation: Department of Biology, University of Tromsø, 9037, Tromsø, Norway, Norway.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Solheim
authors.affiliation: Department of Plant Physiology, Box 117, 221 00, Lund, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Johanson
authors.affiliation: Sheffield Centre for Arctic Ecology, Department of Animal and Plant Sciences, The University of Sheffield, 26 Taptonville Road, Sheffield, S10 5BR, UK.|Abisko Naturvetenskapliga Station, Abisko, 981 07, Sweden.
authors.forename: Terry V
authors.initials: TV
authors.lastname: Callaghan
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: John A
authors.initials: JA
authors.lastname: Lee
authors.affiliation: Institute of Biological Sciences, University of Wales, Aberystwyth, Ceredigion, SY23 3DA, Wales, Australia. DYJ@aber.ac.uk.
authors.forename: Dylan
authors.initials: D
authors.lastname: Gwynn-Jones
authors.affiliation: Department of Cell and Organism Biology, Lund University, 223 62, Lund, Sweden, Sweden.
authors.forename: Lars O
authors.initials: LO
authors.lastname: Björn