Environmental and biochemical controls on the molecular distribution and stable isotope composition of leaf wax biomarkers

Eley, Yvette (2014) Environmental and biochemical controls on the molecular distribution and stable isotope composition of leaf wax biomarkers. Doctoral thesis, University of East Anglia.

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Abstract

Leaf wax n-alkyl lipids are increasingly used as proxies in palaeoclimate studies. Palaeovegetation assemblages are reconstructed from their molecular distribution patterns, while their δ13C and δ2H signals are thought to reflect plant-environment interactions and palaeohydrological shifts, respectively. Such applications depend, however, upon these compounds faithfully recording environmental conditions. To explore the influence of environmental, physical and biochemical controls on n-alkane composition, leaf waxes from seven UK saltmarsh plants were analysed over two growing seasons. Linked analysis of sedimentary n-alkanes enabled further investigation of leaf wax biomarker integration into saltmarsh sediments. The molecular distribution and concentration of n-alkanes from the saltmarsh plants varied significantly. Bulk and n-alkane δ13C recorded different seasonal shifts, with a range of up to 13‰ in the offset between bulk and n-alkane 13C/12C values. This
indicated that post-photosynthetic 13C/12C fractionation may be an important additional control on n-alkane δ13C signals. n-Alkane δ2H also varied among the sampled species by >100‰, and could not be explained by physical processes controlling the movement of water inside/outside and within leaves. Comparison with the 2H/1H of chloroplast-synthesised compounds (fatty acids, phytol) suggested
these differences instead reflected the varied biochemical mechanisms operating in the chloroplast and cytosol. Sedimentary biomarker analysis further highlighted that small/moderate vegetation change could drive shifts of ~40‰ in sedimentary nalkane 2H/1H, while using globally averaged “typical” values to correct for fractionation between source water and n-alkane 2H/1H may not be representative of a specific geographical location. Results demonstrate: (i) the importance of biochemical mechanisms in controlling the molecular and isotopic composition of n-alkyl lipids; and (ii) the need to further constrain the influence of vegetation change on the isotope composition of sedimentary n-alkanes. Future research should address these areas in other biomes and depositional environments, to ensure accurate interpretation of modern and ancient leaf wax lipid data.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Stacey Armes
Date Deposited: 03 Feb 2015 11:21
Last Modified: 03 Feb 2015 11:21
URI: https://ueaeprints.uea.ac.uk/id/eprint/52165
DOI:

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