Distributions and hydrogen isotopic compositions of plant leaf wax from Orinus kokonorica along a general aridity gradient around Lake Qinghai, China

Abstract

To quantitatively analyze the response of distributions and hydrogen isotopic compositions (δD) of plant leaf wax to moisture, and to better understand their implications for paleoclimatic reconstruction, we measured average chain length (ACL) and δD values of n-alkanes and n-fatty acids (n-FAs) from Orinus kokonorica, a typical and representative plant in Lake Qinghai area, along a distance transect extending from lakeshore to wetland to dryland in the arid ecosystem. The results showed that the ACL values of n-alkanes and n-FAs were negatively correlated with soil water content (SWC) with R 2=0.593 and R 2=0.924, respectively. This is as a result of plant’s response to water loss with more abundance in long-chain n-alkyl lipids under increasing aridity by analyzing relationships between the molecular ratios of long-chain n-alkyl lipids (n-alkanes and n-FAs) from O. kokonorica and SWC. The δD values of C29 n-alkane and C28 n-FA were also negatively correlated with SWC with R 2=0.778 and R 2=0.760, respectively, which may due to enhanced D-enrichment in leaf water by evapotranspiration (soil water evaporation and leaf water transpiration) with increasing aridity. Our results demonstrated that moisture exerts a significant control on the ACL and δD values from O. kokonorica in an arid ecosystem. This preliminary study on a modern single plant (O. kokonorica) sets a foundation for comprehending these values as quantitative proxies for paleo-humidity reconstruction.