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An alpine treeline in a carbon dioxide-rich world: synthesis of a nine-year free-air carbon dioxide enrichment study

Dawes, Melissa ; Hagedorn, Frank ; Handa, Ira ; Streit, Kathrin ; Ekblad, Alf ; Rixen, Christian ; Körner, Christian ; Hättenschwiler, Stephan

In: Oecologia, 2013, vol. 171, no. 3, p. 623-637

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    Titre
    • An alpine treeline in a carbon dioxide-rich world: synthesis of a nine-year free-air carbon dioxide enrichment study
    Auteur
    • Dawes, Melissa. Mountain Ecosystems, WSL Institute for Snow and Avalanche Research-SLF, Flüelastrasse 11, 7260, Davos Dorf, Switzerland
    • Hagedorn, Frank. Forest Soils and Biogeochemistry, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903, Birmensdorf, Switzerland
    • Handa, Ira. Département des sciences biologiques, Université du Québec à Montréal (UQÀM), C.P. 8888, succ. Centre-ville, H3C 3P8, Montreal, QC, Canada
    • Streit, Kathrin. Paul Scherrer Institute (PSI), 5232, Villigen, Switzerland
    • Ekblad, Alf. School of Science and Technology, Örebro University, 701 82, Örebro, Sweden
    • Rixen, Christian. Mountain Ecosystems, WSL Institute for Snow and Avalanche Research-SLF, Flüelastrasse 11, 7260, Davos Dorf, Switzerland
    • Körner, Christian. Institute of Botany, University of Basel, Schönbeinstrasse 6, 4056, Basel, Switzerland
    • Hättenschwiler, Stephan. Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), CNRS, 1919 route de Mende, 34293, Montpellier Cedex 5, France
    Type de document
    • Postprint
    Identifiant OAI-PMH
    • oai:doc.rero.ch:319484
    Summary
    We evaluated the impacts of elevated CO2 in a treeline ecosystem in the Swiss Alps in a 9-year free-air CO2 enrichment (FACE) study. We present new data and synthesize plant and soil results from the entire experimental period. Light-saturated photosynthesis (A max) of ca. 35-year-old Larix decidua and Pinus uncinata was stimulated by elevated CO2 throughout the experiment. Slight down-regulation of photosynthesis in Pinus was consistent with starch accumulation in needle tissue. Above-ground growth responses differed between tree species, with a 33% mean annual stimulation in Larix but no response in Pinus. Species-specific CO2 responses also occurred for abundant dwarf shrub species in the understorey, where Vaccinium myrtillus showed a sustained shoot growth enhancement (+11%) that was not apparent for Vaccinium gaultherioides or Empetrum hermaphroditum. Below ground, CO2 enrichment did not stimulate fine root or mycorrhizal mycelium growth, but increased CO2 effluxes from the soil (+24%) indicated that enhanced C assimilation was partially offset by greater respiratory losses. The dissolved organic C (DOC) concentration in soil solutions was consistently higher under elevated CO2 (+14%), suggesting accelerated soil organic matter turnover. CO2 enrichment hardly affected the C-N balance in plants and soil, with unaltered soil total or mineral N concentrations and little impact on plant leaf N concentration or the stable N isotope ratio. Sustained differences in plant species growth responses suggest future shifts in species composition with atmospheric change. Consistently increased C fixation, soil respiration and DOC production over 9years of CO2 enrichment provide clear evidence for accelerated C cycling with no apparent consequences on the N cycle in this treeline ecosystem