Abstract
Compound-specific hydrogen and oxygen isotope analyzes on leaf wax-derived n-alkanes (δ2Hn–alkane) and the hemicellulose-derived sugar arabinose (δ18Oara) are valuable, innovative tools for paleohydrological reconstructions. Previous calibration studies have revealed that δ2Hn–alkane and δ18Oara reflect the isotopic composition of precipitation, but – depending on the region – may be strongly modulated by evapotranspirative enrichment. Since no calibration studies exist for semi-arid and arid Mongolia so far, we have analyzed δ2Hn–alkane and δ18Oara in topsoils collected along a transect through Mongolia, and we compared these values with the isotopic composition of precipitation (δ2Hp–WM and δ18Op–WM, modeled data) and various climate parameters. δ2Hn–alkane and δ18Oara are more positive in the arid south-eastern part of our transect, which reflects the fact that also the precipitation is more enriched in 2H and 18O along this part of the transect. The apparent fractionation εapp, i.e., the isotopic difference between precipitation and the investigated compounds, shows no strong correlation with climate along the transect (ε2H n–C29/p = −129 ± 14‰, ε2H n–C31/p = −146 ± 14‰, and ε18O ara/p = +44 ± 2‰). Our results suggest that δ2Hn–alkane and δ18Oara in topsoils from Mongolia reflect the isotopic composition of precipitation and are not strongly modulated by climate. Correlation with the isotopic composition of precipitation has root-mean-square errors of 13.4‰ for δ2Hn–C29, 12.6 for δ2Hn–C31, and 2.2‰ for δ18Oara, so our findings corroborate the great potential of compound-specific δ2Hn–alkane and δ18Oara analyzes for paleohydrological research in Mongolia.
Introduction
Leaf wax-derived n-alkanes and hemicellulose-derived sugars are produced by higher terrestrial plants and stay well-preserved in soils and sediments, because of their resistance against biochemical degradation (). These compounds and their compound-specific stable hydrogen (δ2Hn–alkane) and oxygen (δ18Osugar) isotopic composition get incorporated into soils through above-ground and root litter, abrasion, as well as grazing (dung), and they have a mean residence time of ∼40 years (leaf wax n-alkanes), while pentoses (including the hemicellulose-derived sugar arabinose) average over ∼20 years (). Since δ2Hn–alkane and δ18Osugar are not strongly affected by degradation effects (, ), they are increasingly used for paleohydrological reconstructions (; , ; ; ; ; ). Usually, they are interpreted to record the isotopic composition of precipitation (, ; ; ; ), which in turn is long acknowledged as a valuable proxy for paleoclimate reconstructions and controlled by e.g., the temperature and amount effect, continentality, and altitude (). The isotopic signal of precipitation can be altered by isotopic fractionation at the soil-plant-atmosphere interface, including evaporative enrichment of soil water (εSW), transpirative enrichment of leaf water (εEt) and biosynthetic fractionation (εbio) (; ; ; ; ).
εSW and εEt can lead to more positive δ2Hn–alkane and δ18Osugar values relative to precipitation and/or the plants source water. εSW is probably of minor importance under semi-arid and arid conditions because most plants (especially perennial plants) exploit deeper water sources that are not isotopically affected by evaporation (; ; ), while εEt has a significant influence on δ2Hn–alkane and δ18Osugar (; ; , ; ; ; ). During biosynthesis, εbio leads to 2H depletion of ∼−160‰ in δ2Hn–alkane values and 18O enrichment of ∼+27‰ in δ18Osugar values. At the same time, it is reported that εbio can vary among plant life forms and plant physiological metabolisms, for different environmental conditions and latitudes, as well as through relative contributions of the strongly depleted NADPH pool (; ; ; ; ; ; ; ; ). The apparent fractionation (ε2H n–alkane/p, ε18O sugar/p), i.e., the difference between the isotopic signature of precipitation/source water (δ2Hp and δ18Op) and δ2Hn–alkane and δ18Osugar, respectively, basically integrates over εSW, εEt and εbio and results in 2H-depleted leaf wax-derived n-alkanes but 18O-enriched hemicellulose-derived sugars relative to δ2Hp and δ18Op (; ; ; ; ).
While some studies suggest that ε2H n–alkane/p in plants and topsoils remains relatively constant over latitudinal distances (, ; ), many others show correlations of ε2H n–alkane/p with relative humidity, mean annual precipitation (MAP) and the aridity index (AI) (, ; ; ; ; ; ). This can be related to more evapotranspirative enrichment under more arid conditions, but plant physiological adaptations might also play a role, as well as changes in vegetation, as e.g., monocotyledons have more negative δ2Hn–alkane values than dicotyledons (; ; ). For relatively arid regions in the United States and South Africa, , , and found no correlations of ε2H n–alkane/p with climate, and they reported constant, but quite different values (−94 ± 21‰, -99 ± 8‰, and −133 ± 12‰, respectively).
So far, only very few calibration studies applied compound-specific δ18Osugar analyzes (; , ; ). For semi-arid and arid regions in South America and South Africa, and suggest enhanced evapotranspirative enrichment and higher ε18O sugar/p values with increasing aridity.
By now, δ2Hn–alkane and δ18Osugar topsoil calibration studies on modern reference material do not exist for semi-arid and arid Mongolia, so it is not clear whether δ2Hn–alkane and δ18Osugar reflect the isotopic composition of precipitation and/or are strongly modulated by evapotranspirative enrichment and climate conditions. Therefore, the aim of this study is to evaluate the influence of different climatic factors on the isotopic composition of leaf wax-derived n-alkanes (δ2Hn–alkane) and the hemicellulose-derived sugar arabinose (δ18Oara) in topsoils from semi-arid and arid Mongolia. More specifically, we addressed the following research questions:
- (1)
Do δ2Hn–alkane and δ18Oara reflect the isotopic composition of precipitation along the investigated transect?
- (2)
Do ε2H n–alkane/p and ε18O ara/p indicate a variable and climate-dependent fractionation on δ2Hn–alkane and δ18Oara?
Our study will provide the necessary basis for using δ2Hn–alkane and δ18Oara for paleohydrological and -climatological reconstructions in semi-arid and arid Mongolia and similar regions.
Materials and Methods
Study Area and Sampling
The semi-arid and arid regions of Mongolia are influenced by three major atmospheric circulation systems (Figure 1A). Summer climate is mainly dominated by the Westerlies and the East Asian summer monsoon (EASM) (; ). Winter climate is dominated by the Siberian high blocking the Westerlies and thus moisture supply during winter (; ). This results in short and hot summers and long, cold, and dry winters and overall harsh conditions (). Especially the vegetation period, during which biosynthesis can take place, is very short and corresponds with the summer months June, July, and August, when ∼75% of the annual precipitation occurs (Figures 1D,E, 2H; ).
FIGURE 1
FIGURE 2
The climate in Mongolia is characterized by increasing mean annual temperature (MAT) and decreasing mean annual precipitation (MAP) toward the south-east (Figure 1C). This climate gradient is mirrored in regional vegetation biomes, well-adapted to the semi-arid and arid conditions of Mongolia. Northern and central Mongolia are characterized by taiga, mountain- and forest steppe biomes, whereas steppe and desert steppe biomes are dominant in southern Mongolia (; ). The precipitation shows a distinct 2Hp–OIPC and 18Op–OIPC enrichment in southern and eastern arid Mongolia (Figure 1A; ), and the seasonal pattern is characterized by isotopically 2H- and 18O-depleted precipitation during winter and 2H- and 18O-enriched precipitation during summer (see Figures 1D,E for δ18Op–OIPC).
For this study, topsoils (0–5 cm) were sampled in LDPE plastic bags in June/July 2017 (ID: 1–33) and June 2016 (ID: 34–42). To prevent molding, samples were stored open and dark during the 2-week field campaigns. Our sampling sites were dominated by different Poaceae and Cyperaceae species (grasses) as well as herbaceous and shrubby growth forms of Artemisia spp. and the woody shrub Caragana spp. Larix sibirica occurred at a few sites (for more details, see ). The investigated transect follows a west-east and north-south gradient with increasing aridity and 2Hp and 18Op enrichment toward eastern and southern Mongolia (Figures 1A,B, 2 – all sampling sites and respective climate parameters are listed in the Supplementary Material).
Biomarker Extraction and Chromatography
Total lipids of 42 topsoils (∼10–35 g) were extracted with dichloromethane:methanol (9:1, v/v) over three cycles using accelerated solvent extraction and ultrasonic extraction. Total lipid extracts were separated over aminopropyl pipette columns (Supelco; 45 μm), n-alkanes were eluted with hexane and additionally cleaned over coupled silver-nitrate (AgNO3) coated silica gel (Supelco, 60–200 mesh) and zeolite (Geokleen Ltd.) pipette columns. n-Alkane identification and quantification were performed on an Agilent 7890B gas chromatograph equipped with an Agilent HP5MS column (30 m × 320 μm × 0.25 μm film thickness) and a flame ionization detector (GC-FID). For identification and quantification, external n-alkane standards (n-alkane mix n-C21 – n-C40, Supelco) were measured with each sequence.
While the n-alkanes had been extracted and quantified in a previous study () and were available and ready for compound-specific δ2H analyzes, we have selected 28 sampling sites for additional sugar analyzes. Hemicellulose-derived sugars were hydrolytically extracted from 0.1 to 1.4 g topsoil material using 10 ml of 4M trifluoroacetic acid at 105°C for 4 h according to . Thereafter, samples were vacuum-filtrated over glass fiber filters and the extracted sugars were cleaned over XAD-7 and Dowex 50WX8 columns to remove humic-like substances and cations (). The purified sugar samples were rotary-evaporated and derivatized with methylboronic acid (4 mg in 400 μl pyridine) at 60°C for 1 h. α-Androstane and 3-O-Methyl-Glucose were used as internal standards ().
Stable Isotope Analyzes
The compound-specific hydrogen isotopic composition of the most abundant n-alkanes (n-C29, n-C31) were measured on an Isoprime Vision isotope ratio mass spectrometer (IRMS) (Elementar, Langenselbold, Germany) coupled to an Agilent 7890B GC (Agilent, Santa Clara, United States) via a GC5 pyrolysis/combustion interface (Elementar, Langenselbold, Germany). The GC5 was operating in pyrolysis mode with a Cr (ChromeHD) reactor at 1050°C. The GC was equipped with a split/splitless injector and an Agilent HP5GC fused silica column (30 m × 320 μm × 0.25 μm film thickness). Samples were injected in splitless mode and measured as triplicates. For normalization, n-alkane standards (n-C27, n-C29, and n-C33) with known isotopic composition (Schimmelmann standard, Indiana) were measured as duplicates after every third sample triplicate. All measurements were drift-corrected relative to the standards in each sequence. The H-correction factor was checked regularly throughout the sequence and yielded stable values of 3.9 ± 0.02 (n = 4). The standard deviation of the sample triplicates was on average 1.2 and 1.0 for n-C29 and for n-C31, respectively, and not worse than 3.6 and 4.7‰. The standard deviation for all standards was better than 2‰ (n = 36). The hydrogen isotopic composition is given in delta notation (δ2H) vs. Vienna Standard Mean Ocean Water (VSMOW).
The compound-specific oxygen isotope measurements were performed on a Trace GC 2000 coupled to a Delta V Advantage IRMS using an 18O-pyrolysis reactor (GC IsoLink) and a ConFlo IV interface (all devices from Thermo Fisher Scientific, Bremen, Germany). Samples were injected in splitless mode and measured in triplicates. For normalization, derivatized sugar standards with known isotopic composition were measured repeatedly at different concentrations within every sequence. Measured δ18O values were drift- and amount-corrected and corrected for the oxygen from the carbonyl group within the sugar molecules that became introduced during the hydrolysis according to . The standard deviation of the sample triplicates was on average 0.4‰, and not worse than 1.2‰. The standard deviation of the arabinose standard was 1.8‰ (n = 24, average over four concentrations). Fucose and xylose concentrations were too low for robust isotope measurements; we therefore refrained from further evaluation of those data. The oxygen isotopic composition is given in delta notation (δ18O) vs. VSMOW.
Data Analysis
Apparent fractionation (εapp) of hydrogen- and oxygen isotopes were calculated after to test for climatic/environmental controls on δ2Hn–alkane (Eq. 1) and δ18Oara (Eq. 2).
δ2Hp–OIPC and δ18Op–OIPC were extracted from The Online Isotopes in Precipitation Calculator (OIPC, Version 3.1)1, the uncertainty estimates (95% confidence interval) range from 1 to 8‰ for δ2Hp–OIPC, and from 0.2 to 0.8‰ for δ18Op–OIPC, respectively (; ; ). Since ∼75% of the annual precipitation occurs during the vegetation period in June, July, and August, an amount-weighted mean (δ2Hp–WM and δ18Op–WM) was used to calculate ε2H n–alkane/p and ε18O ara/p (Eqs. 1, 2). MAT and MAP, as well as the temperature and precipitation of June, July and August (TJJA, PJJA) were extracted from the WorldClim 2.0 dataset (1970–2000, 30 s resolution: )2. The AI and the potential evapotranspiration (Et0) were derived from the Global Aridity Index and Potential Evapotranspiration Climate Database v2 (1970–2000, 30 s resolution: )3. The altitude was extracted from the Shuttle Radar Topography Mission (SRTM) data ().
Correlations of δ2Hn–alkane and δ18Oara with δ2Hp–WM and δ18Op–WM, respectively were tested using weighted linear regressions. Correlations of ε2H n–alkane/p and ε18O ara/p with climate were tested using unweighted linear regressions. Goodness of fit can be assessed using R2, and the accuracy using root-mean-square errors (RMSE). Differences between the arid part of the transect (ID: 34–42) compared to the rest were analyzed using a t-test. For data sets with unequal variance, the Welsh-corrected t-test was used. Statistical analyzes were done using the statistical software Origin 2019b.
Results
Along our investigated transect, δ2Hn–C29 ranges from −215 to −143‰, with an average of −189 ± 16‰. In comparison to δ2Hn–C29, the δ2Hn–C31 values tend to be more 2H-depleted and range from −228 to −154‰ with an average of −205 ± 15‰ (Figure 2A). The δ18Oara values range from +31‰ to +41‰ with an average of +35 ± 3‰ (Figure 2B). All compounds show the same trend as the isotopic composition of precipitation (Figures 2E,F), and are significantly more positive in the arid part of the transect (ID: 34 – 42) compared to the rest (δ2Hn–C29: p = 0.02, δ2Hn–C31: p = 7.08e–4, δ18Oara: p = 2.95e–5). This reflects the 2H and 18O enrichment of the isotopic composition of precipitation, with values ranging from −101 to −53‰ for δ2Hp–OIPC and from −14 to −7‰ for δ18Op–OIPC, respectively. The amount-weighted mean values are more positive and range from −78 to −46‰ for δ2Hp–WM and −11 to −6‰ for δ18Op–WM, respectively. Like the biomarkers, the precipitation is significantly more positive in the arid part of the transect (δ2Hp–WM: p = 1.39e–15, δ18Op–WM: p = 1.32e–17, Figures 2E,F).
ε2H n–C29/p ranges from −165 to −95‰ with an average of −129 ± 14‰ (Figure 2C). In comparison, ε2H n–C31/p is more negative, ranging from −171 to −100‰ with an average of −146 ± 14‰ (Figure 2C). ε18O ara/p ranges from + 39‰ to + 48‰ with an average of + 44 ± 2‰ (Figure 2D). εapp is not statistically different in the arid part of the transect (ε2H n–C29/p: p = 0.79, ε2H n–C31/p: p = 0.554, ε18O ara/p: p = 0.824).
Discussion
Differences in Compound-Specific δ2H
Along the investigated transect δ2Hn–C29 is on average ∼15‰ more positive than δ2Hn–C31. As described previously by , n-C29 is the most abundant homolog in the woody shrubs Caragana spp. and Artemisia spp., whereas n-C31 is the most abundant homolog in grasses. Since shrubs and dicotyledonous plants in general are more sensitive to evapotranspirative enrichment than grasses (; ; ), the observed offset might indicate (i) plant-physiological differences affecting the evapotranspirative enrichment of different plants, and (ii) plant-physiological differences affecting εbio.
Grasses grow via the intercalary meristem, where the leaf water is isotopically not as 2H-enriched due to transpiration compared to the exposed part of grasses (, ; ; ). The leaf wax n-alkanes, which are produced in the intercalary meristem, do therefore not incorporate the full leaf water enrichment signal (; ; ; ; ; ). This can be referred to as “dampening effect”.
δ2Hn–alkane and δ18Oara Against the Isotopic Composition of Precipitation
The δ2Hn–alkane and δ18Oara values correlate significantly with the δ2Hp–WM and δ18Op–WM values (Figure 3, R2 = 0.30, p = 3.22e–4 for δ2Hn–C29; 0.11 and 0.03 for δ2Hn–C31; and 0.36 and 1.60e−3 for δ18Oara). Significant correlations between compound-specific biomarker isotopes and the isotopic composition of precipitation have been observed previously for different regions (a.o.: ; ; ; ; ). In comparison to transects covering larger climate gradients (a.o. ), our determination coefficients are small and explain only up to ∼30% of the variability. However, this is due to the fact that our transect covers only a small climate gradient. The RMSE is 13.4‰ for δ2Hn–C29, 12.6‰ for δ2Hn–C31 and 2.2‰ for δ18Oara (Figure 3) and thus indicates that the biomarkers accurately record the isotopic composition of precipitation along our transect. There are several possible explanations for the observed scatter, including: (i) uncertainties related to the modeled OIPC-based isotopic composition of precipitation and the WorldClim 2.0 reanalysis dataset, (ii) the analytical errors of the δ2Hn–alkane and δ18Oara measurements, (iii) micro-climatic effects along the investigated transect, and (iv) metabolic differences affecting εbio (; ; ; ; ; ; ).
FIGURE 3
Apparent Fractionation Against Climate
To check for potential climatic influences on δ2Hn–alkane and δ18Oara, we correlated apparent fractionation against TJJA, PJJA, Et0 and AI (Figure 4), as well as MAT, MAP, and altitude (Supplementary Figure 1). None of the correlations with climate is significant, except ε2H n–C29/p and precipitation, which is only weak (R2 = 0.20, p = 4.90e−3 for PJJA, and R2 = 0.12, p = 0.03 for MAP). However, if climatically-controlled one might expect that temperature, potential evapotranspiration and the degree of aridity also affect evapotranspirative enrichment and εapp (). Thus, this correlation should not be overinterpreted. We conclude that εapp is nearly constant with ε2H n–C29/p = −129 ± 14‰, ε2H n–C31/p = −146 ± 14‰, and ε18O ara/p = + 44 ± 2‰.
FIGURE 4
Assuming constant εbio values of −160‰ for leaf wax n-alkanes (; ), evapotranspirative enrichment would be ∼31‰ for δ2Hn–C29 and ∼15‰ for δ2Hn–C31 (Figure 4). While n-C29 is the most abundant homolog in shrubs, and n-C31 is the most abundant homolog in grasses (; ) the observed offset in evapotranspirative enrichment most likely results from plant physiological differences described above, particularly the dampening effect. Assuming a constant εbio factor of +27‰ for arabinose (; ) evapotranspirative enrichment would be ∼17‰ for δ18Oara. While we expect arabinose to be mainly synthesized by grasses (), we cannot quantify the contribution from other plants or roots (). Anyhow, for arabinose synthesized by grasses, we can expect a similar dampening effect as described above for leaf waxes, because leaf water in the leaf growth-and-differentiation zone is usually not as enriched as the exposed part of grasses (; ; ).
Comparison With Other Studies
While other calibration studies in relatively arid regions have also not found a strong climatic modulation of ε2H n–alkane/p, our values (−129 ± 14‰ for ε2H n–C29/p and −146 ± 14‰ for ε2H n–C31/p) are only comparable to those from , i.e., −133 ± 12‰ for n-C31 and n-C33, which are much more negative than those reported by and , i.e., −99 ± 8‰ and −92 ± 21‰, respectively. Most likely, plant physiological and metabolic adaptations play an important role, as leaf waxes from C4 plants are more enriched in 2H than leaf waxes from C3 plants, and dicotyledons produce more enriched leaf waxes than monocotyledons (; ; ). reported very similar ε2H n–C29/p values as for Mongolia from the semi-arid and arid regions in China (−127 ± 10‰ compared to −129 ± 14‰), yet ε2H n–C31/p is much less negative than in Mongolia (−133 ± 13‰ compared to −146 ± 14‰). We suggest that this reflects the fact that C4 grasses are more dominant in China than along our transect that is dominated by C3 grasses (). Our ε2H n–C31/p values are also very much comparable to those reported for C3 grass sites along a transect in Europe (), and our ε2H n–C29/p values are in very good agreement with their ε2H n–alkane/p values for sites dominated by deciduous trees, which ones more highlights the dampening effect of C3 grasses compared to dicotyledons.
The ε18O ara/p values for Mongolia (44 ± 2‰) are very similar to values reported by for relatively arid regions in South Africa. There, the more humid regions have a significantly lower ε18O ara/p (∼37‰), quite similar to the C3 grass sites in Europe (). The deciduous tree sites in Europe, however, are again characterized by more enriched δ18Osugar values (ε18O sugar/p = ∼43‰). All this indicates that δ18O is more sensitive to evapotranspirative enrichment than δ2H, so that climate can more strongly modulate δ18Osugar, and again that grasses show the signal dampening much more pronounced than dicotyledons.
Conclusion
This study investigated compound-specific δ2Hn–alkane and δ18Oara values in topsoils collected along a transect through semi-arid and arid Mongolia in order to evaluate to which degree they reflect variations in the isotopic signature of precipitation and/or they are affected by climate and evapotranspirative enrichment. We therefore tested for correlations of δ2Hn–alkane and δ18Oara with δ2Hp–WM and δ18Op–WM, respectively, as well as εapp with climate. We can conclude the following:
- •
Leaf wax-derived n-alkanes and the hemicellulose-derived sugar arabinose are significantly more enriched in 2H and 18O in the more arid southern and eastern parts of the transect. This reflects the changes in the isotopic composition of precipitation along the transect, and the correlations with δ2Hp–WM and δ18Op–WM have RMSE of 13.4‰ for δ2Hn–alkane and 2.2‰ for δ18Oara.
- •
The apparent fractionation remains mostly constant at −129 ± 14‰, −146 ± 14‰, and at + 44 ± 2‰ for ε2H n–C29/p, ε2H n–C31/p and ε18O ara/p, respectively. There are no significant differences along the transect, nor strong correlations with climate.
Compound-specific δ2Hn–alkane and δ18Oara analyzes on terrestrial biomarkers, preserved e.g., in lake sediments, have great potential for reconstructing past changes in the isotopic composition of precipitation and thus for paleoclimate and -hydrological reconstructions in Mongolia.
Statements
Data availability statement
The datasets presented in this study can be found in the article/Supplementary Material.
Author contributions
JS, MB, PS, MZ, and RZ designed the study. MB and RZ collected the samples along transect I in 2016. JS and RZ collected the samples along transect II in 2017. JS carried out the major part of the laboratory analyzes in the laboratory of RZ and BG, assisted by LB, PS, and MB. EB, DA, and WZ organized the sample logistics in 2016 and 2017. JS wrote the manuscript with contributions of all coauthors. All authors contributed to the article and approved the submitted version.
Funding
This research was supported by the SNF (Grant No. PP00P2 – 150590).
Acknowledgments
We thank the Swiss National Science Foundation (SNF) for funding. PS acknowledges the support by a fellowship from the state of Thuringia (Landesgraduiertenstipendium). DA gratefully acknowledges the support of the framework of Goszadanie no. AAAA-A17-117011810038-7. Furthermore, we greatly acknowledge M. Benesch (Martin Luther University Halle-Wittenberg) for compound-specific δ18O measurements and N. Ueberschaar (MS platform, Friedrich-Schiller-University Jena) for providing laboratory facilities. I. K. Schäfer (Agilent) and J. Wintel (Elementar) are acknowledged for support during δ2H measurements. We want to acknowledge H. Maennicke, C. Heinrich, T. Bromm, S. Polifka, M. Lerch (all Martin Luther University Halle-Wittenberg), M. Wagner, F. Freitag, I. Paetz, and N. Blaubach (all Friedrich-Schiller-University Jena) for laboratory support. We thank our logistic partners in Mongolia, especially G. Gereltsogt from Remote Mongolian Adventures and all field trip participants 2016 and 2017. We thank ML and M-AC for their valuable and helpful comments on this manuscript.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Supplementary material
The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/feart.2020.00343/full#supplementary-material
Footnotes
1.^http://www.waterisotopes.org
2.^http://worldclim.org/version2
3.^https://cgiarcsi.community/data/global-aridity-and-pet-database/
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Summary
Keywords
biomarkers, n-alkanes, sugars, compound-specific isotopes, apparent fractionation
Citation
Struck J, Bliedtner M, Strobel P, Bittner L, Bazarradnaa E, Andreeva D, Zech W, Glaser B, Zech M and Zech R (2020) Leaf Waxes and Hemicelluloses in Topsoils Reflect the δ2H and δ18O Isotopic Composition of Precipitation in Mongolia. Front. Earth Sci. 8:343. doi: 10.3389/feart.2020.00343
Received
27 February 2020
Accepted
22 July 2020
Published
10 September 2020
Volume
8 - 2020
Edited by
Moritz Felix Lehmann, University of Basel, Switzerland
Reviewed by
Marco Lehmann, Paul Scherrer Institut (PSI), Switzerland; Marc-Andre Cormier, University of Oxford, United Kingdom
Updates
Copyright
© 2020 Struck, Bliedtner, Strobel, Bittner, Bazarradnaa, Andreeva, Zech, Glaser, Zech and Zech.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Julian Struck, julian.struck@uni-jena.de
This article was submitted to Biogeoscience, a section of the journal Frontiers in Earth Science
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