Hydrogen exchange during cellulose synthesis distinguishes climatic and biochemical isotope fractionations in tree rings

Abstract

Summary• 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)-H 2 ) 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.

Hydrogen dynamics in soil organic matter as determined by <sup>13</sup>C and <sup>2</sup>H labeling experiments

“…It can be weak or strong, depending on the enzyme activated for the degradation of the molecule and the position of the bond (Augusti et al, 2006). When C-H breakdown is favored, the surrounding water imprints its hydrogen isotopic signature on the former bounded H (Augusti et al, 2006). In the present experiment, we show that more than 70 % of the H-C bonds of the initial molecule are broken in the first biodegradation steps (7 days , Fig.…”

“…Moreover, the incorporation of water hydrogen is favored by the strength of the C-H bond breakage. It can be weak or strong, depending on the enzyme activated for the degradation of the molecule and the position of the bond (Augusti et al, 2006). When C-H breakdown is favored, the surrounding water imprints its hydrogen isotopic signature on the former bounded H (Augusti et al, 2006).…”

Detecting long-term metabolic shifts using isotopomers: CO2-driven suppression of photorespiration in C3plants over the 20th century

“…For deuterium NMR measurements, pure samples of a glucose derivative were prepared from all samples, as follows. Soluble sugars were extracted from leaf material according to previously used methods (35,56), starting with 10 g of fresh material. Starch from chloroplasts was extracted from the pellet resulting from extraction of soluble sugars, according to ref.…”

Summer maximum temperature in northern France over the past century: instrumental data versus multiple proxies (tree-ring isotopes, grape harvest dates and forest fires)

“…These processes are similar to those involved in determining the oxygen isotope composition of organic matter. Two specific processes differ: enzymes have kinetic D isotope effects, which discriminate against D in particular C-H groups of metabolites (Augusti et al 2006); during cellulose synthesis, other enzymes act as catalysts for the exchange of ∼40% of hydrogen atoms between xylem water and sugars (Yakir and DeNiro 1990;Terwilliger and DeNiro 1995;Roden et al 2000;Waterhouse et al 2002). The tree effects linked with leaf enrichment, Péclet effect (Barbour et al 2004), and xylem exchanges appear to be quantitatively comparable for oxygen and deuterium (Roden et al 2000).…”