Variability of leaf wax n-alkanes across gradients of environment and plant functional type in China

Abstract

The abundance and distribution of long-chain n-alkanes in sedimentary archives have been proposed as plant-derived paleoenvironmental proxies. The reliable application of these proxies hinges on comprehensive understandings drawn from investigations of living plants. However, previous studies have predominantly relied on narrow environmental gradients and limited datasets sourced from local and regional sampling. As a result, our comprehension of how n-alkanes in living plants respond to climate factors on larger spatial scales remains unclear, especially across different plant functional types (PFTs). In this study, we analyzed the abundance and distribution of n-alkanes in the leaves of 552 plant samples from diverse regions in China and explored the variability of leaf wax n-alkanes across gradients of climate and PFTs. Average chain length (ACL) and carbon preference index (CPI) exhibit statistically significant differences between various PFTs, and the ratio of C33/(C31 + C33) holds the potential to distinguish between C3 and C4 vegetation types. The n-alkane concentration (Σalk) is primarily controlled by precipitation, with a notable negative correlation between Σalk and mean annual precipitation (MAP) that is independent of PFTs. Overall, ACL is negatively related to MAP and positively to mean annual temperature (MAT), but the relationship varies across PFTs. MAT is a stronger driver of ACL for C4 herbs and woody plants, while MAP exerts a more pronounced influence on C3 herbs. CPI in most PFTs shows no correlation with environmental variables. These findings indicate Σalk is a good indicator of precipitation, and ACL is indicative of precipitation or temperature depending on the specific PFT; CPI appears unsuitable as a climate indicator and great caution should be exercised in using CPI records in paleoclimate research.