Oxygen isotope ratios (<sup>18sup>O/<sup>16sup>O) of hemicellulose-derived sugar biomarkers in plants, soils and sediments as paleoclimate proxy I: Insight from a climate chamber experiment

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• 作者：Michael Zech ; Christoph Mayr ; Mario Tuthorn ; Katharina Leiber-Sauheitl ; Bruno Glaser
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：1 February, 2014
• 年：2014
• 卷：126
• 期：Complete
• 页码：614-623
• 全文大小：855 K

文摘

The oxygen isotopic composition of cellulose is a valuable proxy in paleoclimate research. However, its application to sedimentary archives is challenging due to extraction and purification of cellulose. Here we present compound-specific 未<sup>18sup>O results of hemicellulose-derived sugar biomarkers determined using gas chromatography-pyrolysis-isotope ratio mass spectrometry, which is a method that overcomes the above-mentioned analytical challenges. The biomarkers were extracted from stem material of different plants (Eucalyptus globulus, Vicia faba and Brassica oleracea) grown in climate chamber experiments under different climatic conditions.

The 未<sup>18sup>O values of arabinose and xylose range from 31.4鈥?to 45.9鈥?and from 28.7鈥?to 40.8鈥? respectively, and correlate highly significantly with each other (R = 0.91, p < 0.001). Furthermore, 未<sup>18sup>O<sub>hemicellulosesub> (mean of arabinose and xylose) correlate highly significantly with 未<sup>18sup>O<sub>leaf watersub> (R = 0.66, p < 0.001) and significantly with modeled 未<sup>18sup>O<sub>cellulosesub> (R = 0.42, p < 0.038), as well as with relative air humidity (R = 鈭?.79, p < 0.001) and temperature (R = 鈭?.66, p < 0.001). These findings confirm that the hemicellulose-derived sugar biomarkers, like cellulose, reflect the oxygen isotopic composition of plant source water altered by climatically controlled evapotranspirative <sup>18sup>O enrichment of leaf water. While relative air humidity controls most rigorously the evapotranspirative <sup>18sup>O enrichment, the direct temperature effect is less important. However, temperature can indirectly exert influence via plant physiological reactions, namely by influencing the transpiration rate which affects 未<sup>18sup>O<sub>leaf watersub> due to the P茅clet effect. In a companion paper (Tuthorn et al., this issue) we demonstrate the applicability of the hemicellulose-derived sugar biomarker 未<sup>18sup>O method to soils and provide evidence from a climate transect study confirming that relative air humidity exerts the dominant control on evapotranspirative <sup>18sup>O enrichment of leaf water.

Finally, we present a conceptual model for the interpretation of 未<sup>18sup>O<sub>hemicellulosesub> records and propose that a combined 未<sup>18sup>O<sub>hemicellulosesub> and 未<sup>2sup>H<sub>nsub><sub>-alkanesub> biomarker approach is promising for disentangling 未<sup>18sup>O<sub>precipitationsub> variability from evapotranspirative <sup>18sup>O enrichment variability in future paleoclimate studies.