title: Hydrogen exchange during cellulose synthesis distinguishes climatic and biochemical isotope fractionations in tree rings.
abstract: The abundance of the hydrogen isotope deuterium (D) in tree rings is an attractive record of climate; however, use of this record has proved difficult so far, presumably because climatic and physiological influences on D abundance are difficult to distinguish. Using D labelling, we created a D gradient in trees. Leaf soluble sugars of relatively low D abundance entered cellulose synthesis in stems containing strongly D-labelled water. We used nuclear magnetic resonance (NMR) spectroscopy to quantify D in the C-H groups of leaf glucose and of tree-ring cellulose. Ratios of D abundances of individual C-H groups of leaf glucose depended only weakly on leaf D labelling, indicating that the D abundance pattern was determined by physiological influences. The D abundance pattern of tree-ring cellulose revealed C-H groups that exchanged strongly (C(2)-H) or weakly (C(6)-H2) with water during cellulose synthesis. We propose that strongly exchanging C-H groups of tree-ring cellulose adopt a climate signal stemming from the D abundance of source water. C-H groups that exchange weakly retain their D abundance established in leaf glucose, which reflects physiological influences. Combining both types of groups may allow simultaneous reconstruction of climate and physiology from tree rings.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umea University, Sweden.
authors.forename: Angela
authors.initials: A
authors.lastname: Augusti
authors.forename: Tatiana R
authors.initials: TR
authors.lastname: Betson
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schleucher
mesh_terms: D002482:Cellulose / Q000096:biosynthesis*; D002980:Climate; D003903:Deuterium / Q000378:metabolism; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism*; D028222:Picea / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry; D029963:Quercus / Q000378:metabolism*; D012987:Soil / Q000032:analysis; D014867:Water / Q000032:analysis
chemical_list: D012987:Soil; D014867:Water; D006859:Hydrogen; D002482:Cellulose; D003903:Deuterium