The effects of α-cellulose extraction and blue-stain fungus on retrospective studies of carbon and oxygen isotope variation in live and dead trees†
Tree-ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ 13 C and δ 18 O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α-cellulose from live and dead specimens of ponderosa pine ( Pinus ponderosa ), one-seed juniper ( Juniperous monosperma ), piñon pine ( Pinus edulis ) and white fir ( Abies concolor ), including those with fungal growth and beetle frass in the wood, to determine if α-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ 13 C or δ 18 O values of α-cellulose and whole wood was the same for both live and dead trees across a large range of inter-annual and regional climate differences. The method of α-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ 13 C (up to 0.4‰) and δ 18 O (up to 1.2‰) of α-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus ( Ophiostoma ) on the δ 13 C and δ 18 O of whole wood or α-cellulose. The relationships between whole wood and α-cellulose δ 13 C for ponderosa, piñon and juniper yielded slopes of ~1, while the relationship between δ 18 O of whole wood and α-cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States.