COMPOUND-SPECIFIC DELTA-C-13 ANALYSES OF LEAF LIPIDS FROM PLANTS WITHDIFFERING CARBON-DIOXIDE METABOLISMS

The stable carbon isotope (deltaC-13) values of (1) total leaf tissue (2), total surface lipid extracts and (3) individual n-alkanes isolate d from leaves were determined for plants utilizing the C3, C4, and Cra ssulacean Acid (CAM) pathways of carbon fixation. The C4 and CAM speci es had leaf tissue deltaC-13 values of -10 to -16 parts per thousand; the total surface lipid extract deltaC-13 values were on average 8 par ts per thousand more depleted. The C3 plants had leaf tissue values of -25 to -30 parts per thousand; total surface lipid extracts were on a verage 4 parts per thousand. more depleted in C-13. The average n-alka ne values for all plants were around 4 parts per thousand more deplete d in C-13 than the total surface lipid extracts and were between 1.6 a nd 13.8 parts per thousand depleted in C-13 relative to total tissue. This depletion relative to the total tissue was on average greater for CAM (I 1.0 parts per thousand) and C4 plants (9.9 parts per thousand) than for C3 plants (5.9 parts per thousand). Variations ranging from 0.1 to 6 parts per thousand were observed between n-alkane homologues for the plants studied, emphasizing the need for caution when interpre ting small variations in the isotopic compositions of individual compo unds isolated from sedimentary environments. n-Aldehydes from C3 plant s had carbon-isotopic compositions similar to the n-alkanes from the s ame plants, suggesting that other biosynthetically related n-alkyl com pounds (e.g. n-acids and n-alcohols) will have deltaC-13 values simila r to the n-alkanes. Phytol isolated from C3 plants was, on average, 1. 5 parts per thousand enriched in C-13 relative to the average n-alkane deltaC-13 values.