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Variation in Hydrogen Isotope Composition Among Salt Marsh Plant Organic Compounds Highlights Biochemical Mechanisms Controlling Biosynthetic Fractionation
Author(s) -
Eley Yvette,
White Joseph,
Dawson Lorna,
Hren Michael,
Pedentchouk Nikolai
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004403
Subject(s) - fractionation , phytol , isotope fractionation , chemistry , isotopes of nitrogen , isotope , nitrogen , botany , environmental chemistry , biology , organic chemistry , physics , quantum mechanics
Hydrogen isotopes of plant‐derived biomarkers can vary by >100‰ at a single location. Isotope fractionation associated with the movement of water in plant leaves cannot account for this variability alone. Biochemical processes therefore must play a fundamental role in controlling hydrogen isotope fractionation during secondary compound biosynthesis. Different biosynthetic pathways utilize discrete hydrogen pools and occur within distinct cell compartments. We analyzed hydrogen isotope compositions of C 16 and C 18 fatty acids and phytol from seven salt marsh plants and compared these data with (i) leaf water and n ‐alkane δ 2 H, (ii) leaf carbon and nitrogen contents, and (iii) nitrogen isotopes of bulk tissue, to evaluate the relationship between biochemical processes, cellular compartmentalization, and hydrogen isotope fractionation. Interspecies variation in chloroplastic fatty acids and phytol δ 2 H exceeds leaf water δ 2 H, indicating that different commitments of metabolites among species at branching points in chloroplast metabolic processes may be important determinants of lipid δ 2 H values. Dominant osmoregulatory strategies, in particular, show strong correlation with leaf wax n ‐alkane δ 2 H. Species that preferentially produce nitrogenous compounds (dicots/shrubs) as protective solutes have 2 H‐enriched n ‐alkanes relative to species that produce mainly carbohydrates (monocots). n ‐Alkane δ 2 H values, in combination with δ 15 N data and elemental (C, N) composition, together provide information about biochemical environmental adaptations exhibited by different higher plant species in response to environmental stresses. Thus, while spatial and temporal integration of biomarkers may produce an isotopic record of ecosystem function, biomarkers from individual plant or microbial remains may hold additional details into biologic function and adaptation to ancient environments.