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
18O 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18O 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18Ohemicellulose (mean of arabinose and xylose) correlate highly significantly with 未18Oleaf water (R = 0.66, p < 0.001) and significantly with modeled 未18Ocellulose (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 18O enrichment of leaf water. While relative air humidity controls most rigorously the evapotranspirative 18O 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18Oleaf water 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18O method to soils and provide evidence from a climate transect study confirming that relative air humidity exerts the dominant control on evapotranspirative 18O enrichment of leaf water.
Finally, we present a conceptual model for the interpretation of 未18Ohemicellulose records and propose that a combined 未18Ohemicellulose and 未2Hn-alkane biomarker approach is promising for disentangling 未18Oprecipitation variability from evapotranspirative 18O enrichment variability in future paleoclimate studies.