By the same authors

Different response of bulk and n-alkane δ13C signatures to seasonal shifts in environmental conditions in a temperate coastal ecosystem

Research output: Contribution to conferenceAbstractpeer-review

Author(s)

Department/unit(s)

Conference

ConferenceEuropean Geophysical Union
CountryAustria
CityVienna
Conference date(s)27/04/142/05/14

Publication details

DatePublished - 2014
Original languageEnglish

Abstract

The carbon isotope signal recorded in land plants represents an important reservoir of information for reconstructing climatically driven shifts in plant ecophysiology and biochemistry. Analytical advances have led to widespread usage of compound-specific (CS) carbon isotope analysis of leaf wax biomarkers, such as n−alkanes, in addition to traditional bulk isotope methods, to identify shifts in the relative percentage of C3 and C4 vegetation contributing to the sedimentary record. Recent studies, however, have extended the application of leaf wax biomarkers, using bulk and n−alkane δ13C values interchangeably to derive information about plant-environment relations, both in modern ecosystems and throughout the geological past. Even though previous work on C3 plants has shown a clearlink between climatically influenced plant physiology and bulk δ13C values, further research is needed to establish whether the same link can be seen in leaf wax biomarkers.

To address this question, we collected bulk and n−alkane δ13C data from plants growing at Stiffkey marsh on thenorth Norfolk coast, UK over a period of 15 months. Maximum interspecies variation in weighted average (WA) n−alkane δ13C among C3 species was typically 2-3‰ greater than in bulk. We observed a close correlation in the bulk and WA n−alkane δ13C seasonal trends from C3 grasses and reeds (R2=0.9, P <0.05). However, for other species (including C3 and C4 plants), no statistically significant relationship was observed between their respective bulk and WA n−alkane carbon isotope values. This variation in δ13C trends resulted in considerable intra- and inter-species variability (ranging from -4 to -13 per mil) in the offset between bulk and WA n−alkane δ13C values. In addition, we identified a positive correlation (R2=0.7, P <0.05), for all species (with the exception of the evergreen succulent Suaeda vera) between the relative abundance of the n−C25 and n−C27 n−alkane homologues and n−C29 alkane δ13C values. 

We explain the discrepancy between bulk and n−alkane δ13C signatures by referring to possible interspecies variation in post-photosynthetic carbon isotope fractionation. Our data imply that for some species, seasonal changesin the abundance of n−alkane homologues might be an important biochemical process influencing n−alkane δ13C signatures. We further theorise that interspecies variation in n−alkane δ13C values may arise from biochemical  differences in salinity adaptation - in plants adapted to salt stress, production of osmoregulatory solutes (amino acids and/or carbohydrates) may influence the partitioning of pyruvate to fates other than acetyl-CoA, shifting the isotopic composition of lipid biomarkers. Mechanisms controlling metabolic fluxes through these biochemical processes may potentially exert an additional important control over the δ13C signal of lipid biomarkers.We therefore conclude that it may not be valid to use bulk and n−alkane δ13C data interchangeably to examine plant-environment interactions. These findings open new avenues for empirical studies to further understand the metabolic processes fractionating carbon during the synthesis of leaf wax lipids, enhancing interpretation of the biomarker signal from the geological record. 

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