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  • 1. Bjerke, J W
    et al.
    Gwynn-Jones, D
    Callaghan, T V
    Effects of enhanced UV-B radiation in the field on the concentration of phenolics and chlorophyll fluorescence in two boreal and arctic-alpine lichens2005In: Environmental and Experimental Botany, ISSN 0098-8472, E-ISSN 1873-7307, Vol. 53, no 2, p. 139-149Article in journal (Refereed)
    Abstract [en]

    Lichens constitute a prominent part of the vegetation at high latitudes and altitudes, but the effects of UV-B radiation on these symbiotic organisms are not well known. In a northern boreal site (Abisko, northern Sweden), the usnic acid-producing lichens Flavocetraria nivalis and Nephroma arcticum were exposed to enhanced UV-B radiation, corresponding to 25% ozone depletion, for two and one growing seasons, respectively. They were compared with lichens grown under ambient UV-B and harvested fresh from the field. The treated thalli of F nivalis had been transplanted from a site 24 km from the treatment site. From this source locality, untreated thalli were also harvested. Enhanced UV-B did not affect concentrations of usnic acid and the two depsides phenarctin and nephroarctin. A gradual decline of usnic acid, probably coupled to unusually long periods of dry, sunny weather, was observed both under enhanced and ambient UV-B and in untreated thalli. Photosystem II efficiency in both species was slightly reduced by enhanced UV-B. However, differences between seasons were larger than differences between treatments, which indicate that UV-B effects are minor in comparison to other climatic variables. Concentrations of UV-B-absorbing phenolics in lichens do not show a simple relationship to UV-B dose and therefore cannot be used as bioindicators of UV-B levels. (c) 2004 Elsevier B.V. All rights reserved.

  • 2. Rinnan, Riikka
    et al.
    Rinnan, Ņsmund
    Faubert, Patrick
    Tiiva, Päivi
    Holopainen, Jarmo K.
    Michelsen, Anders
    Few long-term effects of simulated climate change on volatile organic compound emissions and leaf chemistry of three subarctic dwarf shrubs2011In: Environmental and Experimental Botany, ISSN 0098-8472, E-ISSN 1873-7307, Vol. 72, no 3, p. 377-386Article in journal (Refereed)
    Abstract [en]

    Climate change is exposing arctic ecosystems to higher temperature, increased nutrient availability and shading due to the increasing cloud cover and the expanding forests. In this work, we assessed how these factors affect the emissions of biogenic volatile organic compounds (BVOCs) from three subarctic dwarf shrub species in a field experiment after 18 treatment years. Of the studied species the willow Salix phylicifolia L. was the only isoprene-emitter with an emission potential of 16.1 ± 8.4 μg g−1 dw h−1 (at 30 °C and photosynthetic photon flux density of 1000 μmol m−2 s−1). The dwarf birch Betula nana L. had significant emissions of various reactive BVOCs, including monoterpenes and sesquiterpenes. The evergreen Cassiope tetragona (L.) D. Don emitted high amounts of mono- and sesquiterpenes. Due to chance, the temperature in the warming treatment (employing open-top plastic tents) and the unwarmed treatments was similar at the time of the measurements, and therefore long-term indirect effects of warming could be assessed without interference of temperature differences at the time of measurement. The long-term warming had not altered foliar N, P or condensed tannin concentrations, but it had led to other chemical changes detected in the near-infrared reflectance spectra of the leaves. Nevertheless, there were no significant differences in the BVOC emissions per unit leaf mass measured by the dynamic enclosure method and gas chromatography-mass spectrometry. Annual additions of NPK fertilizer, which mimicked increased nutrient availability, had accumulated P in the leaves of all species. In addition, fertilization marginally increased the leaf N concentration of B. nana. The only significant fertilization effect on BVOC emissions was a stimulation of emission of the sesquiterpene β-selinene from S. phylicifolia. The shading treatment obtained by dome-shaped hessian tents did not cause clear long-term changes in leaf chemistry or BVOC emissions. The only observed change was a marginally significant increase in sesquiterpene emissions from B. nana. When the treatment effects on long-term biomass changes in the different treatments were taken into account by proportioning the BVOC emissions to the biomass of each species in the field treatments, warming led to a significant increase and shading to a decrease in the total BVOC emissions per unit ground area from B. nana. These results highlight the importance of an integrated approach for realistic assessment of responses to climate change.

    Research highlights

    ▶ Long-term warming altered near-infrared reflectance spectra of the leaves. ▶ NPK fertilization increased foliar P and, for Betula nana, N concentration. ▶ Warming, fertilization and shading had few effects on BVOC emissions per unit leaf mass. ▶ On square meter basis, warming increased total BVOC emission from B. nana.

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