Abstract
Abstract. Leaf wax n-alkane patterns and their compound-specific δ13C signatures are valuable proxies for paleoenvironmental reconstructions. So far, their potential has not been investigated in semi-arid to arid Mongolia. We have therefore analysed the leaf wax n-alkanes and their compound-specific δ13C signature of five plant species (Poaceae, Cyperaceae, Artemisia spp., Caragana spp. and Larix sp.) and topsoils (0–5 cm) along two transects in central and southern Mongolia. Grasses show a distinct dominance of the n-C31 homologue, whereas the shrubs Caragana spp. and Artemisia spp. are dominated by n-C29. Larix sp. is characterised by the mid-chain n-alkanes n-C23 and n-C25. From plant to topsoil, n-alkane patterns show the potential to differentiate between grass-covered sites from those covered by Caragana spp. n-Alkane concentrations and odd-over-even predominance (OEP) of the topsoils are distinctly influenced by mean annual temperature, mean annual precipitation and aridity, likely reflecting the degree of n-alkane degradation and biomass production. In contrast, the average chain length (ACL) and the n-alkane ratio (n-C31∕n-C29+n-C31) are not affected by climatic parameters and, thus, are not biased by climate. The compound-specific δ13C signatures are strongly correlated to climate, showing a significant enrichment with increasing aridity, indicating the effect of water use efficiency. Our calibration results suggest that long-chain n-alkanes and their compound-specific δ13C signatures have great potential to reconstruct paleoenvironmental and paleoclimatic conditions when used in sediment archives from Mongolia.
Highlights
Leaf wax biomarkers such as long-chain n-alkanes (n-C25 − n-C35) are produced in the plant cuticle as a protection layer against environmental stress and are synthesised by the polyketide biosynthetic pathway, resulting in a distinct odd-over-even predominance (OEP; Eglinton and Hamilton, 1967; Shepherd and Wynne Griffiths, 2006)
N-alkane patterns show the potential to differentiate between grass-covered sites from those covered by Caragana spp. n-Alkane concentrations and odd-over-even predominance (OEP) of the topsoils are distinctly influenced by mean annual temperature, mean annual precipitation and aridity, likely reflecting the degree of n-alkane degradation and biomass production
Several studies have shown a strong correlation between the δ13C leaf wax signal of C3 plants and water use efficiency (WUE) that is influenced by precipitation, temperature and evapotranspiration and describes the stomata conductance of a plant to avoid water loss (Diefendorf and Freimuth, 2017; Farquhar et al, 1982; Rao et al, 2017)
Summary
Leaf wax biomarkers such as long-chain n-alkanes (n-C25 − n-C35) are produced in the plant cuticle as a protection layer against environmental stress and are synthesised by the polyketide biosynthetic pathway, resulting in a distinct odd-over-even predominance (OEP; Eglinton and Hamilton, 1967; Shepherd and Wynne Griffiths, 2006). When interpreting leaf wax n-alkanes and their compound-specific δ13C signature several potential pitfalls, such as species-specific and intra-leaf variations (Diefendorf et al, 2011; Gao et al, 2015), the influence of environmental and climatic factors (Carr et al, 2014; Diefendorf and Freimuth, 2017; Farquhar et al, 1982; Hoffmann et al, 2013; Rao et al, 2017; Tipple et al, 2013), the dependency on altitude (Feakins et al, 2018; Hultine and Marshall, 2000), and n-alkane degradation (Brittingham et al, 2017; Buggle et al, 2010; Li et al, 2018a), have to be considered and accounted for Such regional calibration studies on recent leaf wax n-alkane patterns, compound-specific δ13C and potential climatic biases on the leaf wax signal do not exist for Mongolia. Loess–paleosol and colluvial sediment archives have been increasingly investigated in semi-arid and arid Mongolia and could potentially be used for future paleoenvironmental reconstructions based on leaf wax n-alkanes (Klinge et al, 2017; Peck et al, 2002; Prokopenko et al, 2007; Rudaya and Li, 2013; Wang et al, 2011)
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