title: The diel imprint of leaf metabolism on the δ13 C signal of soil respiration under control and drought conditions.
abstract: Recent (13) CO(2) canopy pulse chase labeling studies revealed that photosynthesis influences the carbon isotopic composition of soil respired CO(2) (δ(13) C(SR)) even on a diel timescale. However, the driving mechanisms underlying these short-term responses remain unclear, in particular under drought conditions. The gas exchange of CO(2) isotopes of canopy and soil was monitored in drought/nondrought-stressed beech (Fagus sylvatica) saplings after (13) CO(2) canopy pulse labeling. A combined canopy/soil chamber system with gas-tight separated soil and canopy compartments was coupled to a laser spectrometer measuring mixing ratios and isotopic composition of CO(2) in air at high temporal resolution. The measured δ(13) C(SR) signal was then explained and substantiated by a mechanistic carbon allocation model. Leaf metabolism had a strong imprint on diel cycles in control plants, as a result of an alternating substrate supply switching between sugar and transient starch. By contrast, diel cycles in drought-stressed plants were determined by the relative contributions of autotrophic and heterotrophic respiration throughout the day. Drought reduced the speed of the link between photosynthesis and soil respiration by a factor of c. 2.5, depending on the photosynthetic rate. Drought slows the coupling between photosynthesis and soil respiration and alters the underlying mechanism causing diel variations of δ(13) C(SR).
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Barthel
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Albin
authors.initials: A
authors.lastname: Hammerle
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Sturm
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Baur
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Lydia
authors.initials: L
authors.lastname: Gentsch
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, 8092 Zürich, Switzerland.|Büsgen-Insitute, Chair of Bioclimatology, Georg-August-University Göttingen, Büsgenweg 2, 37077 Göttingen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Knohl
mesh_terms: D018533:Biomass; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism; D002247:Carbon Isotopes; D019069:Cell Respiration; D055864:Droughts; D029964:Fagus / Q000378:metabolism*; D016013:Likelihood Functions; D008954:Models, Biological; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism*; D012987:Soil; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D012987:Soil; D002244:Carbon