Compound-specific δD-δ¹³C analyses of n-alkanes extracted from terrestrial and aquatic plants

Stable hydrogen and carbon isotopic compositions of individual n-alkanes were determined for various terrestrial plants (33 samples including 27 species) and aquatic plants (six species) in natural environments from Japan and Thailand. In C3 plants, n-alkanes extracted from angiosperms have a δD value of -152 ± 26‰ (relative to Standard Mean Ocean Water [SMOW]) and δ¹³C value of -36.1 ± 2.7‰ (relative to Peedde Belemnite [PDB]), and those from gymnosperms have a δD value of -149 ± 16‰ and δ¹³C value of -31.6 ± 1.7‰. Angiosperms have n-alkanes depleted in ¹³C relative to gymnosperms. n-Alkanes from C4 plants have a δD value of -171 ± 12‰ and δ¹³C value of -20.5 ± 2.1‰, being a little depleted in D and much enriched in ¹³C compared to C3 plants. n-Alkanes of CAM plants are a little depleted in D and vary widely in δ¹³C relative to those of C3 and C4 plants. In aquatic plants, n-alkanes from freshwater plants have a δD value of -187 ± 16‰ and δ¹³C value of -25.3 ± 1.9‰, and those from seaweeds have a δD value of -155 ± 34‰ and δ¹³C value of -22.8 ± 1.0‰. All n-alkanes from various plant classes are more depleted in D and ¹³C relative to environmental water and bulk tissue, respectively. In addition, the hydrogen and carbon isotopic fractionations during n-alkane synthesis are distinctive for these various plant classes. While C3 plants have smaller isotopic fractionations in both D and ¹³C, seaweed has larger isotopic fractionations.