Corrigendum: Leaf Waxes and Hemicelluloses in Topsoils Reflect the δ2H and δ18O Isotopic Composition of Precipitation in Mongolia

A Corrigendum on
Leaf Waxes and Hemicelluloses in Topsoils Reflect the δ²H and δ¹⁸O Isotopic Composition of Precipitation in Mongolia

by Struck, J., Bliedtner, M., Strobel, P., Bittner, L., Bazarradnaa, E., Andreeva, D., Zech, W., Glaser, B., Zech, M., and Zech, R. (2020). Front. Earth Sci. 8:343. doi: 10.3389/feart.2020.00343

In the original article, the presented δ¹⁸O_ara values were accidentally not corrected for the oxygen introduced during hydrolysis. The necessary correction results in slightly more positive δ¹⁸O_ara values.

The authors apologize for this mistake, and state that this does not change the scientific conclusions of the article in any way, particularly the fact that the calculated apparent fractionation (Ɛ_{18O ara/p}) is constant along the Mongolian transect. However, as the apparent fractionation is 44 ± 2‰ (not 41 ± 2‰) and this would affect future data compilations and comparisons, we have corrected all δ¹⁸O_ara and Ɛ_{18O ara/p} values in the text, the figures, and the supplementary material. We delete our hypothesis stated in the Supplementary Material that a decreasing partial CO₂ pressure might cause enhanced ¹⁸O_ara enrichment, because the correlation between Ɛ_{18O ara/p} and altitude is not significant anymore (R² = 0.09, p = 0.14). All changes are highlighted in bold.

A correction has been made to the Abstract. The corrected version is as follows:

“The apparent fractionation Ɛ_app, i.e., the isotopic difference between precipitation and the investigated compounds, shows no strong correlation with climate along the transect (Ɛ_{2H n-C29/p} = −129 ± 14‰, Ɛ_{2H n-C31/p} = −146 ± 14‰, and Ɛ_{18O ara/p} = +44 ± 2‰). Our results suggest that δ²H_n-alkane and δ¹⁸O_ara 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 δ²H_n-C29, 12.6 for δ²H_n-C31, and 2.2‰ for δ¹⁸O_ara, so our findings corroborate the great potential of compound-specific δ²H_n-alkane and δ¹⁸O_ara analyzes for paleohydrological research in Mongolia”.

A correction has been made to the Results. The corrected version is as follows:

“The δ¹⁸O_ara 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 (δ²H_n-C29: p = 0.017, δ²H_n-C31: p = 7.08e⁻⁴, δ¹⁸O_ara: p = 2.95e⁻⁵).

FIGURE 2

FIGURE 2. δ²H and δ¹⁸O signatures of leaf wax-derived n-alkanes and the hemicellulose sugar arabinose as well as their apparent isotope fractionation (Ɛ_app), compared to environmental and climatic parameters along the transect (A) Compound-specific δ²H of the leaf wax-derived n-alkane n-C₂₉ (black) and n-C₃₁ (green) (this study) (B) compound-specific δ¹⁸O_ara (this study) (C) Ɛ_{2H n-C29/p} (black) and Ɛ_{2H n-C31/p} (green) (this study) (D) Ɛ_{18O ara/p} (this study) (E, F) OIPC isotopic composition of precipitation (black line) and amount-weighted isotopic signature of precipitation (blue line): δ²H_p(E), and δ¹⁸O_p(F), respectively (Bowen et al., 2005; Bowen, 2019; Fick and Hijmans, 2017; IAEA/WMO, 2015) (G) the potential evapotranspiration (Et₀) (Trabucco and Zomer, 2019) (H) mean annual temperature (MAP) (Fick and Hijmans, 2017) (I) averaged summer temperature of June, July, and August (T_JJA) (J) black line shows the mean annual precipitation (MAP), blue shaded area the summer precipitation amount (P_JJA) (Fick and Hijmans, 2017) (K) the aridity index (AI) (Trabucco and Zomer, 2019), and (L) the altitude (Jarvis et al., 2008).

Ɛ_{18O ara/p} ranges from +39‰ to +48‰ with an average of +44 ± 2‰ (Figure 2D). Ɛ_app is not statistically different in the arid part of the transect (Ɛ_{2H n-C29/p}: p = 0.791, Ɛ_{2H n-C31/p}: p = 0.554, Ɛ_{18O ara/p}: p = 0.824)”.

A correction has been made to Discussion, δ²H_n-alkaneand δ¹⁸O_araAgainst the Isotopic Composition of Precipitation. The corrected version is as follows:

“The δ²H_n-alkane and δ¹⁸O_ara values correlate significantly with the δ²H_p-WM and δ¹⁸O_p-WM values (Figure 3, R² = 0.30, p = 3.22e⁻⁴ for δ²H_n-C29; 0.11 and 0.03 for δ²H_n-C31; and 0.36 and 1.60e⁻³ for δ¹⁸O_ara).

FIGURE 3

FIGURE 3. δ²H signatures of the leaf wax-derived n-alkanes (A)n-C₂₉ and (B)n-C₃₁, as well as (C) δ¹⁸O_ara signatures from the topsoil transect through Mongolia plotted against the amount-weighted δ²H and δ¹⁸O signature of precipitation (δ²H_p-WM/δ¹⁸O_p-WM). Red trend lines illustrate linear regressions, gray shaded areas the 95% confidence interval. Bold R²/p-values indicate the level of significance (α = 0.05).

The RMSE is 13.4‰ for δ²H_n-C29, 12.6‰ for δ²H_n-C31 and 2.2‰ for δ¹⁸O_ara (Figure 3) and thus indicates that the biomarkers accurately record the isotopic composition of precipitation along our transect”.

A correction has been made to Discussion, Apparent Fractionation Against Climate. The corrected version is as follows:

“Thus, this correlation should not be over interpreted. We conclude that Ɛ_app is nearly constant with Ɛ_{2H n-C29/p} = −129 ± 14‰, Ɛ_{2H n-C31/p} = −146 ± 14‰, and Ɛ_{18O ara/p} = +44 ± 2‰.

Assuming a constant Ɛ_bio factor of +27‰ for arabinose (Lehmann et al., 2017; Hepp et al., 2020) evapotranspirative enrichment would be ∼17‰ for δ¹⁸O_ara”.

A correction has been made to Discussion, Comparison With Other Studies. The corrected version is as follows:

“The Ɛ_{18O ara/p} values for Mongolia (44 ± 2‰) are similar to values reported by Strobel et al. (2020) for relatively arid regions in South Africa. There, the more humid regions have a significantly lower Ɛ_{18O ara/p} (∼37‰), quite similar to the C₃ grass sites in Europe (Hepp et al., 2020). The deciduous tree sites in Europe, however, are again characterized by more enriched δ¹⁸O_sugar values (Ɛ_{18O sugar/p} = ∼43‰). All this indicates that δ¹⁸O is more sensitive to evapotranspirative enrichment than δ²H, so that climate can more strongly modulate δ¹⁸O_sugar, and again that grasses show the signal dampening much more pronounced than dicotyledons”.

A correction has been made to the Conclusion. The corrected version is as follows:

“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 δ²H_p-WM and δ¹⁸O_p-WM have RMSE of 13.4‰ for δ²H_n-alkane and 2.2‰ for δ¹⁸O_ara.

The apparent fractionation remains mostly constant at −129 ± 14‰, −146 ± 14‰, and at +44 ± 2‰ for Ɛ_{2H n-C29/p}, Ɛ_{2H n-C31/p} and Ɛ_{18O ara/p}, respectively. There are no significant differences along the transect, nor strong correlations with climate”.

A correction has been made to the Supplementary Material, Apparent Fractionation Against Climate. The corrected version is as follows:

“In addition to climate, we correlated the Ɛ_app values against altitude, to test for altitude-controlled evapotranspirative enrichment. In contrast to a previous study by Polissar and Freeman (2010), no impact could be observed for δ²H_n-alkaneand δ¹⁸O_ara, with Ɛ_{2H n-C29/p,} Ɛ_{2H n-C31/p}and Ɛ_18Oara/p being constant along our investigated transect (Supplementary Figure 1)”.

The corrected caption for Supplementary Figure 1 is as follows:

“The corrected δ¹⁸O_ara values affect the presented data in Figures 2–4, and the Supplementary Figure 1”.

FIGURE 4

FIGURE 4. Apparent fractionation Ɛ_{2H n-C29/p}, Ɛ_{2H n-C31/p} and Ɛ_{18O ara/p} from the topsoil transect through Mongolia plotted against T_JJA, P_JJA, Et₀, AI (Fick and Hijmans, 2017; Trabucco and Zomer, 2019). Red trend lines illustrate linear regressions, gray shaded areas the 95% confidence interval. Bold R²/p-values indicate the level of significance (α = 0.05). Black dashed lines illustrate values for the biosynthetic fractionation, and black arrows indicate the effect of evapotranspirative enrichment (biosynthetic fractionation factors of −160‰ and +27‰ are assumed for the n-alkanes and arabinose, respectively).

The authors apologize for these errors and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.

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.

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.2020.619100/full#supplementary-material.

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