title: Environmental drivers of carbon and nitrogen isotopic signatures in peatland vascular plants along an altitude gradient.
abstract: Peatlands are important sinks of atmospheric carbon (C) that, in response to climate warming, are undergoing dynamic vegetation succession. Here we examined the hypothesis that the uptake of nutrients by different plant growth forms (PGFs) is one key mechanism driving changes in species abundance in peatlands. Along an altitude gradient representing a natural climate experiment, we compared the variability of the stable C isotope composition (δ(13)C) and stable nitrogen (N) isotope composition (δ(15)N) in current-year leaves of two major PGFs, i.e. ericoids and graminoids. The climate gradient was associated with a gradient of vascular plant cover, which was parallelled by different concentrations of organic and inorganic N as well as the fungal/bacterial ratio in peat. In both PGFs the (13)C natural abundance showed a marginal spatial decrease with altitude and a temporal decrease with progression of the growing season. Our data highlight a primary physical control of foliar δ(13)C signature, which is independent from the PGFs. Natural abundance of foliar (15)N did not show any seasonal pattern and only in the ericoids showed depletion at lower elevation. This decreasing δ(15)N pattern was primarily controlled by the higher relative availability of organic versus inorganic N and, only for the ericoids, by an increased proportion of fungi to bacteria in soil. Our space-for-time approach demonstrates that a change in abundance of PGFs is associated with a different strategy of nutrient acquisition (i.e. transfer via mycorrhizal symbiosis versus direct fine-root uptake), which could likely promote observed and predicted dwarf shrub expansion under climate change.
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL Site Lausanne, Station 2, 1015, Lausanne, Switzerland.|Ecole Polytechnique Fédérale de Lausanne EPFL, School of Architecture, Civil and Environmental Engineering ENAC, Laboratory of Ecological Systems ECOS, Station 2, 1015, Lausanne, Switzerland.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Gavazov
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL Site Birmensdorf, 8903, Birmensdorf, Switzerland.
authors.forename: Frank
authors.initials: F
authors.lastname: Hagedorn
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL Site Lausanne, Station 2, 1015, Lausanne, Switzerland.|Ecole Polytechnique Fédérale de Lausanne EPFL, School of Architecture, Civil and Environmental Engineering ENAC, Laboratory of Ecological Systems ECOS, Station 2, 1015, Lausanne, Switzerland.|Laboratoire de Chrono-Environnement, UMR CNRS 6249, UFR des Sciences et Techniques, Université de Franche-Comté, Besançon, 25030, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Buttler
authors.affiliation: Paul Scherrer Institute PSI, 5232, Villigen, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Siegwolf
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL Site Lausanne, Station 2, 1015, Lausanne, Switzerland. luca.bragazza@wsl.ch.|Ecole Polytechnique Fédérale de Lausanne EPFL, School of Architecture, Civil and Environmental Engineering ENAC, Laboratory of Ecological Systems ECOS, Station 2, 1015, Lausanne, Switzerland. luca.bragazza@wsl.ch.|Department of Life Science and Biotechnologies, University of Ferrara, Corso Ercole I d'Este 32, Ferrara, 44121, Italy. luca.bragazza@wsl.ch.
authors.forename: Luca
authors.initials: L
authors.lastname: Bragazza
mesh_terms: D000531:Altitude; D001419:Bacteria / Q000254:growth & development; D002244:Carbon / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis; D002980:Climate; D057231:Climate Change; D029785:Cyperaceae; D017753:Ecosystem; D029791:Ericaceae; D005658:Fungi / Q000254:growth & development; D019684:Magnoliopsida / Q000033:anatomy & histology / Q000254:growth & development* / Q000382:microbiology; D038821:Mycorrhizae; D009584:Nitrogen / Q000378:metabolism; D009587:Nitrogen Isotopes / Q000032:analysis; D063245:Plant Development; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D006109:Poaceae; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D013559:Symbiosis
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D012987:Soil; D002244:Carbon; D009584:Nitrogen
keywords: 13C; 15N; Ericoids; Fungal/bacterial ratio; Graminoids; Leaf chemistry; Stable isotope ratio