Chemical pretreatment of Thuja occidentalis tree rings: implications for dendroisotopic studies

Whether or not extractives, lignin, and (or) hemicelluloses, all of which have specific isotopic signatures, should be removed prior to dendroisotopic analysis is still debated. This study reports the range of modern tree-ring delta 13C values of cellulose from Thuja occidentalis L., a species that has been under-utilized in dendroisotopic research despite its broad distribution and great longevity in North America. The main objective of the study was to recommend a wood component from T. occidentalis to isolate for future delta 13C dendroisotopic analyses. Annually resolved tree-ring decadal segments common to eight T. occidentalis trees were excised from cross sections and homogenized. The tree-ring decadal segment from each tree was then chemically processed from untreated whole wood to extractive-free wood, to holocellulose, and to alpha-cellulose. Subsamples were analyzed for delta 13C, percent carbon, and percent yield after each stage of chemical treatment. We recommend that holocellulose be extracted for T. occidentalis, as the alpha-cellulose yield may be too low when tree-ring samples are very small. The delta 13C values for T. occidentalis tree rings were found to be enriched with respect to those for needle-leaved conifers but in close agreement with those reported in the literature for other scale-leaved evergreens.