Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Rapid Commun Mass Spectrom. 2011 Oct 30;25(20):3083-90. doi: 10.1002/rcm.5192.
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.
活树和近期死亡树木的树轮碳和氧同位素比值可能揭示树木死亡的重要机制。然而，死树的木材腐朽可能会改变整个木材的 δ(13)C 和 δ(18)O 值，从而掩盖与导致生理死亡的因素相关的同位素信号。我们研究了来自美国西部森林的活树和死树的边材全木和 α-纤维素，包括有真菌生长和蛀木甲虫粪便的样本，以确定是否需要提取 α-纤维素才能准确解释死树的同位素组成。我们发现，在很大的年际和区域气候差异范围内，活树和死树的 α-纤维素和全木之间的 δ(13)C 或 δ(18)O 值的偏移是相同的。α-纤维素提取方法，无论是 Leavitt-Danzer 还是适用于小样本的 Standard Brendel 方法，都会对 α-纤维素的 δ(13)C（高达 0.4‰）和 δ(18)O（高达 1.2‰）产生显著影响，这是其他研究报告的结果。蛀木甲虫粪便或蓝变真菌（Ophiostoma）对全木或 α-纤维素的 δ(13)C 和 δ(18)O 没有影响。在白皮松、矮松和刺柏中，全木和 α-纤维素 δ(13)C 之间的关系呈 ~1 的斜率，而全木和 α-纤维素 δ(18)O 之间的关系则不太明确。我们的结论是，在美国西部森林中进行树木死亡率同位素模式的回溯研究几乎没有分析或采样障碍。
