Seasonality of the altitude effect on leaf wax n-alkane distributions, hydrogen and carbon isotopes along an arid transect in the Qinling Mountains.

Abstract

Reconstructing paleoelevation allows the temporal evolution of biogeochemical processes and hydroclimate regimes to be understood and quantified. A dual-isotope biomarker of clumped hydrogen and carbon isotopes of leaf wax n-alkanes was recently proposed in humid tropical forests, and it was proven to be superior to a single-isotope proxy that was previously reported. However, it remains unknown whether the dual-isotope biomarker is suitable in arid conditions. The present study investigated leaf wax n-alkane distribution, hydrogen (δ2Hwax) and carbon (δ13Cwax) isotopes in terrestrial plants along an arid mountainous transect. We found that the effects of seasonality on n-alkane distribution, δ2Hwax and δ13Cwax were minimal for all species (p>0.05), and that species-specific δ2Hwax values remained almost unchanged for most species, in contrast to δ13Cwax values. Significant correlations between altitude and δ2Hwax values (R2=0.54, 0.58, and 0.75 for spring, summer, and autumn, respectively), instead of δ13Cwax values (R2=0.08, 0.43, and 0.12 with p=0.24, 0.01, and 0.19 for spring, summer, and autumn, respectively), were observed, suggesting that δ2Hwax values, but not δ13Cwax values, can be reliably used as a proxy for reconstructing paleoelevation in arid conditions. Therefore, it will be necessary to identify other proxies to supplement δ2Hwax values under a dual-isotope approach in future research.