Roden J S, Ehleringer J R
Stable Isotope Ratio Facility for Environmental Research, Department of Biology, University of Utah, Salt Lake City 84112-0840, USA.
Isotopes Environ Health Stud. 2000;36(3):303-17. doi: 10.1080/10256010008036389.
The isotopic composition of tree-ring cellulose was obtained over a two-year period from small diameter, riparian zone trees along an elevational transect in Big Cottonwood Canyon, Utah, USA to test for a possible temperature dependence of net biological fractionation during cellulose synthesis. The isotope ratios of stream water varied by only 3.6% and 0.2% in deltaD and delta18O, respectively, over an elevation change of 810m. The similarity in stream water and macroenvironment over the short (13km) transect produced nearly constant stem and leaf water deltaD and delta18O values. In addition, what few seasonal variations observed in the isotopic composition of source water and atmospheric water vapor or in leaf water evaporative enrichment were experienced equally by all sites along the elevational transect. The temperature at each site along the transect spanned a range of > or = 5 degrees C as calculated using the adiabatic lapse rate. Since the deltaD and delta18O values of stem and leaf water varied little for these trees over this elevation/temperature transect, any differences in tree-ring cellulose deltaD and delta18O values should have been associated with temperature effects on net biological fractionation. However, the slopes of the regressions of elevation versus the deltaD and delta18O values of tree-ring cellulose were not significantly different from zero indicating little or no temperature dependence of net biological fractionation. Therefore, cross-site climatic reconstruction studies using the isotope ratios of cellulose need not be concerned that temperatures during the growing season have influenced results.
在美国犹他州大棉白杨峡谷，沿着海拔梯度从河岸带小直径树木获取了为期两年的树木年轮纤维素的同位素组成，以测试纤维素合成过程中净生物分馏可能存在的温度依赖性。在810米的海拔变化范围内，溪水的同位素比率在δD和δ18O中分别仅变化了3.6%和0.2%。在短（13千米）梯度上溪水和宏观环境的相似性使得树干和树叶水的δD和δ18O值几乎保持恒定。此外，在源水和大气水汽的同位素组成或树叶水蒸发富集方面观察到的少量季节变化，海拔梯度上的所有站点都同样经历了。根据绝热递减率计算，该梯度上每个站点的温度跨度≥5摄氏度。由于在这个海拔/温度梯度上这些树木的树干和树叶水的δD和δ18O值变化很小，树木年轮纤维素δD和δ18O值的任何差异都应该与温度对净生物分馏的影响有关。然而，海拔与树木年轮纤维素δD和δ18O值的回归斜率与零没有显著差异，这表明净生物分馏几乎没有或不存在温度依赖性。因此，利用纤维素同位素比率进行跨站点气候重建研究无需担心生长季节的温度会影响结果。
