Comparison between δ13C of α-cellulose and bulk wood in the mangrove tree Rhizophora mucronata: Implications for dendrochemistry

Stable carbon isotope analysis of tree rings has become a widely used proxy in environmental and palaeoclimatological studies. In those studies, α-cellulose has often been the preferred material because of its singular composition and its immobility in wood. However, cellulose extraction is a time-consuming procedure and since the development of on-line isotope ratio mass spectrometers has become the time-limiting step in the isotopic analysis of wood samples for dendrochemical purposes. In this study we evaluate the necessity of cellulose extraction for isotopic analysis of tree rings in a tropical mangrove tree, Rhizophora mucronata Lam. Comparison between the δ13C of extracted α-cellulose and bulk wood material revealed a highly significant linear relationship (δ13Cbulk wood = 0.92 (± 0.08) * δ13Cα-cellulose − 2.91 (± 2.04); p < 0.001) for α-cellulose values between −24‰ and −27‰. However α-cellulose was on average 0.97 ± 0.03‰ enriched in 13C as compared to bulk wood. The slope of the regression was not significantly different from one (p < 0.05). Furthermore, no significant difference was found between either the δ13Cbulk wood − δ13Cα-cellulose slopes for earlywood and latewood or between the slopes for samples from trees growing in contrasting environmental conditions. These results indicate that bulk wood can be used instead of α-cellulose when measuring stable carbon isotopes in the sapwood of R. mucronata in the context of a dendrochronological investigation.