title: Stable isotopes in tree rings: towards a mechanistic understanding of isotope fractionation and mixing processes from the leaves to the wood.
abstract: The mechanistic understanding of isotope fractionation processes is increasing but we still lack detailed knowledge of the processes that determine the isotopic composition of the tree-ring archive over the long term. Especially with regard to the path from leaf photosynthate production to wood formation, post-assimilation fractionations/processes might cause at least a partial decoupling between the leaf isotope signals that record processes such as stomatal conductance, transpiration and photosynthesis, and the wood or cellulose signals that are stored in the paleophysiological record. In this review, we start from the rather well understood processes at the leaf level such as photosynthetic carbon isotope fractionation, leaf water evaporative isotope enrichment and the issue of the isotopic composition of inorganic sources (CO2 and H2O), though we focus on the less explored 'downstream' processes related to metabolism and transport. We further summarize the roles of cellulose and lignin as important chemical constituents of wood, and the processes that determine the transfer of photosynthate (sucrose) and associated isotopic signals to wood production. We cover the broad topics of post-carboxylation carbon isotope fractionation and of the exchange of organic oxygen with water within the tree. In two case studies, we assess the transfer of carbon and oxygen isotopic signals from leaves to tree rings. Finally we address the issue of different temporal scales and link isotope fractionation at the shorter time scale for processes in the leaf to the isotopic ratio as recorded across longer time scales of the tree-ring archive.
authors.affiliation: Institute for Landscape Biogeochemistry, Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalderstr. 84, 15374 Müncheberg, Germany Long-term Forest Ecosystem Research (LWF), Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Switzerland arthur.gessler@wsl.ch.
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
authors.affiliation: Department of Crop and Forest Science-AGROTECNIO Center, University of Lleida, Avda Rovira Roure 191, 25198 Lleida, Spain.
authors.forename: Juan Pedro
authors.initials: JP
authors.lastname: Ferrio
authors.affiliation: Institute for Landscape Biogeochemistry, Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalderstr. 84, 15374 Müncheberg, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Hommel
authors.affiliation: Research Unit Landscape Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Switzerland.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Treydte
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitaetsstrasse 2, 8092 Zurich, Switzerland.
authors.forename: Roland A
authors.initials: RA
authors.lastname: Werner
authors.affiliation: School of Natural Resources and the Environment and Laboratory for Tree Ring Research, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Russell K
authors.initials: RK
authors.lastname: Monson
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism; D008031:Lignin / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism*; D018526:Plant Transpiration; D013395:Sucrose / Q000378:metabolism; D014197:Trees / Q000254:growth & development* / Q000378:metabolism; D014934:Wood / Q000254:growth & development* / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D013395:Sucrose; D002244:Carbon; D002482:Cellulose; D008031:Lignin; D010100:Oxygen
keywords: Cellulose; evaporative enrichment; oxygen atom exchange; phloem transport; post-photosynthetic; storage