title: Soil H₂¹⁸O labelling reveals the effect of drought on C¹⁸OO fluxes to the atmosphere.
abstract: Above- and belowground processes in plants are tightly coupled via carbon and water fluxes through the soil-plant-atmosphere system. The oxygen isotopic composition of atmospheric CO₂ and water vapour (H₂Ov) provides a valuable tool for investigating the transport and cycling of carbon and water within this system. However, detailed studies on the coupling between ecosystem components and environmental drivers are sparse. Therefore, we conducted a H2 (18)O-labelling experiment to investigate the effect of drought on the speed of the link between below- and aboveground processes and its subsequent effect on C(18)OO released by leaves and soils. A custom-made chamber system, separating shoot from soil compartments, allowed separate measurements of shoot- and soil-related processes under controlled conditions. Gas exchange of oxygen stable isotopes in CO₂ and H₂Ov served as the main tool of investigation and was monitored in real time on Fagus sylvatica saplings using laser spectroscopy. H₂(18)O-labelling showed that drought caused a slower transport of water molecules from soil to shoot, which was indicated by its direct derivation from independently measured concentrations and (18)O/(16)O ratios of CO₂ and H₂Ov, respectively. Furthermore, drought reduced the (18)O equilibrium between H₂O and CO₂ at the shoot level, resulting in less-enriched C(18)OO fluxes from leaf to atmosphere compared with control plants. Compared with the shoot, (18)O equilibrium was not instantaneous in the soil and no drought effect was apparent.
authors.affiliation: Ecosystems and Global Change, Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand Institute of Agricultural Sciences, ETH Zürich, Universitätsstrasse 2, 8092 Zurich, Switzerland mbarthel@ethz.ch.
authors.forename: Matti
authors.initials: M
authors.lastname: Barthel
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätsstrasse 2, 8092 Zurich, Switzerland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Sturm
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätsstrasse 2, 8092 Zurich, Switzerland Institute of Ecology, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria.
authors.forename: Albin
authors.initials: A
authors.lastname: Hammerle
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätsstrasse 2, 8092 Zurich, Switzerland.
authors.forename: Nina
authors.initials: N
authors.lastname: Buchmann
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätsstrasse 2, 8092 Zurich, Switzerland Chair of Bioclimatology, Georg-August University of Göttingen, Büsgenweg 2, D-37077 Göttingen, Germany.
authors.forename: Lydia
authors.initials: L
authors.lastname: Gentsch
authors.affiliation: Laboratory for Atmospheric Chemistry/Stable Isotopes & Ecosystem Fluxes, PSI - Paul Scherrer Institute, 5232 Villigen, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Siegwolf
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Universitätsstrasse 2, 8092 Zurich, Switzerland Chair of Bioclimatology, Georg-August University of Göttingen, Büsgenweg 2, D-37077 Göttingen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Knohl
mesh_terms: D001272:Atmosphere; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D055864:Droughts; D029964:Fagus / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010103:Oxygen Isotopes / Q000032:analysis; D018515:Plant Leaves / Q000502:physiology; D012987:Soil; D014867:Water / Q000378:metabolism*
chemical_list: D010103:Oxygen Isotopes; D012987:Soil; D014867:Water; D002245:Carbon Dioxide; D002244:Carbon; D010100:Oxygen
keywords: Above/belowground; C18OO; Fagus sylvatica; H2
  18O; coupling; drought; laser spectroscopy.