title: The impact of an inverse climate-isotope relationship in soil water on the oxygen-isotope composition of Larix gmelinii in Siberia.
abstract: Stable oxygen isotope ratios (δ(18) O) in trees from high latitude ecosystems are valuable sources of information for recent and past environmental changes, but the interpretation is hampered by the complex hydrology of forests growing under permafrost conditions, where only a shallow layer of soil thaws in summer. We investigated larch trees (Larix gmelinii) at two sites with contrasting soil conditions in Siberia and determined δ(18) O of water from different soil depths, roots, twigs, and needles as well as δ(18) O of soluble carbohydrates regularly over two growing seasons. A comparison of results from the 2 yrs revealed an unexpected 'inverse' climate-isotope relationship, as dry and warm summer conditions resulted in lower soil and root δ(18) O values. This was due to a stronger uptake of isotopically depleted water pools originating from melted permafrost or previous winter snow. We developed a conceptual framework that considers the dependence of soil water profiles on climatic conditions for explaining δ(18) O in needle water, needle soluble carbohydrates and stem cellulose. The negative feedback of drought conditions on the source isotope value could explain decreasing tree-ring δ(18) O trends in a warming climate and is likely relevant in many ecosystems, where a soil isotope gradient with depth is observed.
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, 5232, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Saurer
authors.affiliation: V.N. Sukachev Institute of Forest, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, 660036, Russia.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Kirdyanov
authors.affiliation: V.N. Sukachev Institute of Forest, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, 660036, Russia.
authors.forename: Anatoly S
authors.initials: AS
authors.lastname: Prokushkin
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, 5232, Switzerland.
authors.forename: Katja T
authors.initials: KT
authors.lastname: Rinne
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, 5232, Switzerland.
authors.forename: Rolf T W
authors.initials: RT
authors.lastname: Siegwolf
mesh_terms: D002241:Carbohydrates / Q000032:analysis; D002980:Climate; D055864:Droughts; D017753:Ecosystem; D006813:Humidity; D028221:Larix / Q000378:metabolism*; D008834:Microclimate; D010103:Oxygen Isotopes; D018515:Plant Leaves / Q000737:chemistry; D018517:Plant Roots / Q000737:chemistry; D011336:Probability; D012800:Siberia; D012987:Soil / Q000737:chemistry*; D012995:Solubility; D014867:Water / Q000737:chemistry*
chemical_list: D002241:Carbohydrates; D010103:Oxygen Isotopes; D012987:Soil; D014867:Water
keywords: Craig-Gordon model; cellulose; leaf water enrichment; oxygen isotope; permafrost; soil water