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 delta C-13 and delta O-18 values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and a-cellulose from live and dead specimens of ponderosa pine (Pinus ponderosa), one-seed juniper (Juniperous monosperma), pi on pine (Pinus edulis) and white fir (Abies concolor), including those with fungal growth and beetle frass in the wood, to determine if a-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the delta C-13 or delta O-18 values of a-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 a-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the delta C-13 (up to 0.4 parts per thousand) and delta O-18 (up to 1.2 parts per thousand) of a-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus (Ophiostoma) on the delta C-13 and delta O-18 of whole wood or a-cellulose. The relationships between whole wood and a-cellulose delta C-13 for ponderosa, pi on and juniper yielded slopes of similar to 1, while the relationship between delta O-18 of whole wood and alpha-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. Published in 2011 by John Wiley & Sons, Ltd.