title: Stable Water Use Efficiency under Climate Change of Three Sympatric Conifer Species at the Alpine Treeline.
abstract: The ability of treeline associated conifers in the Central Alps to cope with recent climate warming and increasing CO2 concentration is still poorly understood. We determined tree ring stable carbon and oxygen isotope ratios of Pinus cembra, Picea abies, and Larix decidua trees from 1975 to 2010. Stable isotope ratios were compared with leaf level gas exchange measurements carried out in situ between 1979 and 2007. Results indicate that tree ring derived intrinsic water-use efficiency (iWUE) of P. cembra, P. abies and L. decidua remained constant during the last 36 years despite climate warming and rising atmospheric CO2. Temporal patterns in Δ(13)C and Δ(18)O mirrored leaf level gas exchange assessments, suggesting parallel increases of CO2-fixation and stomatal conductance of treeline conifer species. As at the study site soil water availability was not a limiting factor iWUE remained largely stable throughout the study period. The stability in iWUE was accompanied by an increase in basal area increment (BAI) suggesting that treeline trees benefit from both recent climate warming and CO2 fertilization. Finally, our results suggest that iWUE may not change species composition at treeline in the Austrian Alps due to similar ecophysiological responses to climatic changes of the three sympatric study species.
authors.affiliation: Department of Alpine Timberline Ecophysiology, Federal Research and Training Centre for Forests, Natural Hazards and Landscape Innsbruck, Austria.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wieser
authors.affiliation: Institute of Botany, Leopold-Franzens-Universität Innsbruck Innsbruck, Austria.
authors.forename: Walter
authors.initials: W
authors.lastname: Oberhuber
authors.affiliation: Institute of Botany, Leopold-Franzens-Universität Innsbruck Innsbruck, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Gruber
authors.affiliation: Department of Alpine Timberline Ecophysiology, Federal Research and Training Centre for Forests, Natural Hazards and Landscape Innsbruck, Austria.
authors.forename: Marco
authors.initials: M
authors.lastname: Leo
authors.affiliation: Ecophysiology of Plants, Department of Ecology and Ecosystem Management, Technische Universität München Freising, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Matyssek
authors.affiliation: Ecophysiology of Plants, Department of Ecology and Ecosystem Management, Technische Universität München Freising, Germany.
authors.forename: Thorsten Erhard Edgar
authors.initials: TE
authors.lastname: Grams
keywords: Central Alps; climate change; intrinsic water use efficiency; stable isotopes; tree growth; treeline