Hydrogen and carbon isotopic fractionations of lipid biosynthesis among terrestrial (C3, C4 and CAM) and aquatic plants

Compound-specific hydrogen and carbon isotopic compositions in n-alkanoic acids, phytol and sterols were determined for various plant classes (terrestrial C3-angiosperm; C3-gymnosperm; C4; crassulacean acid metabolism (CAM); and aquatic C3 plants) in order to investigate isotopic fractionations among various plant classes. In all plants, lipid biomolecules are depleted in both D (up to 324‰) and ¹³C (up to 14.7‰) relative to ambient water and bulk tissue, respectively. In addition, the magnitude of D- and ¹³C-depletion of lipid biomolecules is distinctive depending on plant classes. For example, C3 angiosperm n-alkanoic acids are less depleted in D (95±23‰) and ¹³C (4.3±2.5‰) relative to ambient water and bulk tissue, respectively, while C4 plant n-alkanoic acids are more depleted in D (119±15‰) and ¹³C (10.2±2.0‰). On the other hand, C3 angiosperm phytol and sterols are much more depleted in D (306±12‰ for phytol, 211±15‰ for sterol) with less depletion in ¹³C (4.1±1.1‰ for phytol, 1.3±0.9‰ for sterol) relative to ambient water and bulk tissue, respectively, while C4 plant phytol and sterols are less depleted in D (254±7‰ for phytol, 186±13‰ for sterols) with much more depletion in ¹³C (9.0±1.2‰ for phytol, 5.0±1.1‰ for sterols). Among various plant classes, there is a positive correlation between the D- and ¹³C-depletion for n-alkanoic acids, while a negative correlation was found for phytol and sterols from the same plants.