© 2006 Heron Publishing—Victoria, Canada
A multi-species comparison of δ13C from whole wood, extractive-free wood and holocellulose
B. A. Harlow (1, 2, 4), J. D. Marshall (1) and A. P. Robinson (3)
1. Department of Forest Resources, University of Idaho, Moscow, ID 83844-1133, USA / 2. School of Biological Sciences, Washington State University, P.O. Box 644236, Pullman, WA 99164, USA / 3. Department of Mathematics and Statistics, University of Melbourne, Parkville, Victoria 3010, Australia / 4. Corresponding author (bharlow@wsu.edu) / Received March 9, 2005; accepted September 28, 2005; published online March 1, 2006
Summary
The stable carbon (C) isotope composition (δ13C) of tree rings is a powerful metric for reconstructing past physiological responses to climate variation. However, accurate
measurement and interpretation are complicated by diagenesis and the translocation of compounds with distinct isotopic signatures.
Isolation and analysis of cellulose minimizes these complications by eliminating variation due to biosynthetic pathways; however,
isolation of cellulose is time-consuming and has no clear endpoint. A faster and better-defined analytical method is desirable.
Our objectives were to determine if there is a direct relationship between the isotopic compositions of whole wood (WW), whole
wood treated with solvents to remove mobile extractives (extractive-free wood; EF) and holocellulose (HC) isolated by extractive
removal and subsequent bleaching. We also determined if total C concentration could explain the isotopic composition and variation
among these three wood components of each sample. A set of wood samples of diverse phylogeny, anatomy and chemical composition,
was examined. The mean offset or difference between HC and EF δ13C was 1.07 ± 0.09‰ and the offset between HC and WW was 1.32 ± 0.10‰. Equivalence tests (with α = 0.05) indicated that the
relationship between EF δ13C and HC δ13C had a slope significantly similar to 1 ± 5.5%, whereas for the WW δ13C: HC δ13C relationship, the slope was significantly similar to 1 ± 10.08%. A regression model using EF δ13C to predict HC δ13C had a slope of 0.97, which was not significantly different from unity (P = 0.264), whereas the regression for WW had a slope of 0.92 which was significantly different from unity (P = 0.0098). Carbon concentration was correlated with HC:WW offset and cellulose:EF offset (P = 0.0501 and 0.007, respectively), but neither relationship explained much of the variation (r2 = 0.12 and 0.14, respectively). We suggest that HC extraction is unnecessary for most analyses of tree-ring δ13C; a simple solvent extraction is a suitable alternative for many applications.
Keywords:
stable carbon isotope ratio, climate change, diagenesis, translocation.
