Branched alkanes with quaternary carbon atoms in Chinese soils: Potential environmental implications

Abstract

Lipids extracted from 26 modern soils collected from different climate zones in China and Mongolia are analyzed using gas chromatographymass spectrometry. These extracts contain pseudohomologous families of 5,5-diethylalkanes (5,5-DEAs), 6,6-diethylalkanes, 5-butyl-5-ethylalkanes and 6-butyl-6-ethylalkanes, which are first detected in modern soils. All these pseudohomologous series display exclusively odd or exclusively even carbon numbers, clearly indicating a biosynthetic origin, and their carbon number distributions generally covary. The distributions of 5,5-DEAs exhibit strong regional variations, correlated with the spatial distributions of climate and vegetation. The lower molecular weight 5,5-DEAs, maximizing at C 21 or C 23 , dominate in southeast and southwest China samples, while the higher molecular weight 5,5-DEAs with a mode at C 29 dominate in cold, arid northwest China and Mongolia. The results demonstrate that the distribution of 5,5-DEAs can serve as a new independent proxy, indicating variations in soil ecosystems and climates, just like the well-known proxy of n-C 15 -21 /n-C 22 -33 ratios.

Chemical characterization of microbial-dominated soil organic matter in the Garwood Valley, Antarctica

“…Both n-alkylcyclopentanes and n-alkylcyclohexanes ranged from C 16 to C 24 with C max at C 18 -C 20 . A similar distribution of BAQCs, alkylcyclopentanes and alkylcyclohexanes has been reported in soils, ancient sediments, sedimentary rocks, and Antarctic cyanobacterial mats (Kenig et al, 2003(Kenig et al, , 2005Bai et al, 2006;Jungblut et al, 2009). However, recent investigations reporting the presence of these compounds in the extracts of polyethylene bags suggest that they are most probably derived from contamination (Grosjean and Logan, 2007;Brocks et al, 2008).…”

Holocene vegetation signals in the Alashan Desert of northwest China revealed by lipid molecular proxies from calcareous root tubes

“…The n -alkane distributions demonstrate that all of the woody vegetation (shrubs) maximizes at C 27 and most of the herbaceous vegetation maximizes at C 31 or C 33 (Liu and Huang, 2005; Zhong et al, 2009; Liu and Liu, 2015). Moreover, n -alkanes from modern topsoil with herbaceous vegetation maximize at C 31 in the western Loess Plateau (Wang et al, 2003; Zhong et al, 2009), whereas n -alkanes from modern topsoil with woody vegetation (shrubs) maximize at C 27 or C 29 in the arid region of northwestern China (Bai et al, 2006a, 2006b). Therefore, we interpreted the n -alkane C max as a proxy of vegetation in the Alashan Desert, with the n -alkanes C 27 or C 29 indicating woody vegetation and the n -alkanes C 31 or C 33 indicating herbaceous vegetation.…”

Assessing biomarker syngeneity using branched alkanes with quaternary carbon (BAQCs) and other plastic contaminants

“…2,2-dimethyl-, 5,5-diethyl and 3,3,x3,x3-tetraethylalkanes. Based on their apparent occurrence in specific environments, BAQCs were construed as biomarkers for non-photosynthetic, sulfide oxidizing prokaryotes that predominantly inhabit benthic redox boundaries (Kenig et al, 2003) or identified as new proxies indicating variations in soil ecosystems and climates (Bai et al, 2006). However, a biogenic source of BAQCs can be excluded for several reasons.…”