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

Abstract

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 per thousand ) and 13C (up to 14.7 per thousand ) 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 per thousand ) and 13C (4.3 +/- 2.5 per thousand ) relative to ambient water and bulk tissue, respectively, while C4 plant n-alkanoic acids are more depleted in D (119 +/- 15 per thousand ) and 13C (10.2 +/- 2.0 per thousand ). On the other hand, C3 angiosperm phytol and sterols are much more depleted in D (306 +/-12 per thousand for phytol, 211+/-15 per thousand for sterol) with less depletion in 13C (4.1 +/- 1.1 per thousand for phytol, 1.3 +/- 0.9 per thousand for sterol) relative to ambient water and bulk tissue, respectively, while C4 plant phytol and sterols are less depleted in D (254 +/- 7 per thousand for phytol, 186 +/- 13 per thousand for sterols) with much more depletion in 13C (9.0 +/- 1.2 per thousand for phytol, 5.0 +/- 1.1 per thousand 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.