title: Pinus sylvestris switches respiration substrates under shading but not during drought.
abstract: Reduced carbon (C) assimilation during prolonged drought forces trees to rely on stored C to maintain vital processes like respiration. It has been shown, however, that the use of carbohydrates, a major C storage pool and apparently the main respiratory substrate in plants, strongly declines with decreasing plant hydration. Yet no empirical evidence has been produced to what degree other C storage compounds like lipids and proteins may fuel respiration during drought. We exposed young scots pine trees to C limitation using either drought or shading and assessed respiratory substrate use by monitoring the respiratory quotient, δ(13) C of respired CO2 and concentrations of the major storage compounds, that is, carbohydrates, lipids and amino acids. Only shaded trees shifted from carbohydrate-dominated to lipid-dominated respiration and showed progressive carbohydrate depletion. In drought trees, the fraction of carbohydrates used in respiration did not decline but respiration rates were strongly reduced. The lower consumption and potentially allocation from other organs may have caused initial carbohydrate content to remain constant during the experiment. Our results suggest that respiratory substrates other than carbohydrates are used under carbohydrate limitation but not during drought. Thus, respiratory substrate shift cannot provide an efficient means to counterbalance C limitation under natural drought.
authors.affiliation: Max-Planck Institute for Biogeochemistry, Hans Knoll Str. 10, 07745, Jena, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fischer
authors.affiliation: Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745, Jena, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hanf
authors.affiliation: Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745, Jena, Germany.|Institute for Physical Chemistry, Friedrich Schiller University, Helmholtzweg 4, 07743, Jena, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Frosch
authors.affiliation: Max-Planck Institute for Biogeochemistry, Hans Knoll Str. 10, 07745, Jena, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Gleixner
authors.affiliation: Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745, Jena, Germany.|Institute for Physical Chemistry, Friedrich Schiller University, Helmholtzweg 4, 07743, Jena, Germany.|Abbe Center of Photonics, Friedrich Schiller University, Helmholtzweg 4, 07743, Jena, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Popp
authors.affiliation: Max-Planck Institute for Biogeochemistry, Hans Knoll Str. 10, 07745, Jena, Germany.
authors.forename: Susan
authors.initials: S
authors.lastname: Trumbore
authors.affiliation: Max-Planck Institute for Biogeochemistry, Hans Knoll Str. 10, 07745, Jena, Germany.
authors.forename: Henrik
authors.initials: H
authors.lastname: Hartmann
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes; D019069:Cell Respiration; D055864:Droughts; D006813:Humidity; D010788:Photosynthesis; D041605:Pinus sylvestris / Q000166:cytology* / Q000502:physiology*; D012987:Soil / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D012987:Soil; D014867:Water; D002245:Carbon Dioxide
keywords: carbon starvation; hydration; respiratory quotient; respiratory substrates; stress physiology; tree ecophysiology; tree mortality