title: CO2 enrichment alters diurnal stem radius fluctuations of 36-yr-old Larix decidua growing at the alpine tree line.
abstract: To understand how trees at high elevations might use water differently in the future, we investigated the effects of CO2 enrichment and soil warming (separately and combined) on the water relations of Larix decidua growing at the tree line in the Swiss Alps. We assessed diurnal stem radius fluctuations using point dendrometers and applied a hydraulic plant model using microclimate and soil water potential data as inputs. Trees exposed to CO2 enrichment for 9 yr showed smaller diurnal stem radius contractions (by 46 ± 16%) and expansions (42 ± 16%) compared with trees exposed to ambient CO2 . Additionally, there was a delay in the timing of daily maximum (40 ± 12 min) and minimum (63 ± 14 min) radius values for trees growing under elevated CO2 . Parameters optimized with the hydraulic model suggested that CO2 -enriched trees had an increased flow resistance between the xylem and bark, representing a more buffered water supply system. Soil warming did not alter diurnal fluctuation dynamics or the CO2 response. Elevated CO2 altered the hydraulic water flow and storage system within L. decidua trees, which might have contributed to enhanced growth during 9 yr of CO2 enrichment and could ultimately influence the future competitive ability of this key tree-line species.
authors.affiliation: Mountain Ecosystems, WSL Institute for Snow and Avalanche Research - SLF, Flüelastrasse 11, CH-7260, Davos Dorf, Switzerland.
authors.forename: Melissa A
authors.identifier: http://orcid.org/0000-0003-4919-0151
authors.initials: MA
authors.lastname: Dawes
authors.affiliation: Ecophysiology, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland.
authors.forename: Roman
authors.initials: R
authors.lastname: Zweifel
authors.affiliation: Snow Cover and Micrometeorology, WSL Institute for Snow and Avalanche Research - SLF, Flüelastrasse 11, CH-7260, Davos Dorf, Switzerland.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Dawes
authors.affiliation: Mountain Ecosystems, WSL Institute for Snow and Avalanche Research - SLF, Flüelastrasse 11, CH-7260, Davos Dorf, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Rixen
authors.affiliation: Biogeochemistry, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland.
authors.forename: Frank
authors.initials: F
authors.lastname: Hagedorn
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology*; D002940:Circadian Rhythm / Q000187:drug effects; D028221:Larix / Q000187:drug effects* / Q000502:physiology; D024301:Plant Bark / Q000187:drug effects / Q000502:physiology; D018547:Plant Stems / Q000187:drug effects / Q000502:physiology; D018526:Plant Transpiration / Q000187:drug effects; D012987:Soil; D013696:Temperature; D014197:Trees; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000187:drug effects / Q000502:physiology
chemical_list: D012987:Soil; D014867:Water; D002245:Carbon Dioxide
keywords: European larch (Larix decidua); Swiss Alps; dendrometer; free-air CO2 enrichment (FACE); global change; soil warming; tree water relations