Investigating the carbon isotope composition and leaf wax n-alkane concentration of C-3 and C-4 plants in Stiffkey saltmarsh, Norfolk, UK

摘要

The carbon isotope composition of terrestrial plants records valuable ecophysiological and palaeoecological information. However, interspecies variability in C-13/C-12, at both the bulk and compound-specific (CS) level, requires further exploration across a range of ecosystem types. Here, we present bulk and n-alkane delta C-13 values, and n-alkane concentrations, from seven plants (C-3 and C-4) growing in a temperate UK saltmarsh. Inter-and intra-species variation in n-alkane delta C-13 values among C-3 plants ranged from 8%(n-C-31) to 10% (n-C-27) across the 2011 and 2012 growing seasons, exceeding variability in bulk tissue (7%). In contrast, the C-4 monocot showed <2% seasonal shifts in bulk and CS values. As a result of the variability in our CS data, we calculate that n-alkane based C-3/C-4 reconstructions in temperate saltmarshes have a maximum uncertainty of similar to 11%. For dicots and succulents, seasonal bulk and CS delta C-13 trends diverged, while for C-3 and C-4 monocots, bulk and CS values followed similar temporal patterns. Fractionation between bulk and n-alkane carbon isotope values varied from -4 to -10% for C-3 plants, and reached -13% for the C-4 monocot. We explain discrepancies between bulk and n-alkane delta C-13 values by referring to possible interspecies variation in salinity adaptation, which may influence the partitioning of pyruvate, shifting the isotopic composition of lipid biomarkers. These findings open new avenues for empirical studies to further understand the metabolic processes fractionating carbon during the synthesis of n-alkanes, enhancing interpretation of the biomarker signal from the geological record. (C) 2016 Elsevier Ltd. All rights reserved.