Compound Specific D/H Isotopes of Lipids and Carbohydrates from C3 and C4 Extant Plants

There are limited studies on the fractionations of hydrogen associated with photosynthesis in higher plants. The stable hydrogen isotope composition of individual lipids, as well as bulk stable hydrogen isotopes of total biomass, total lipids and total residue (after lipid extraction) from different terrestrial C3 and C4 plants grown under chamber conditions are under investigation. D/H and D/H ¹⁸ O of (1) leaf water and soil water isolated cryogenically from each plant type (2) watervapour in the greenhouse and (3) irrigation water were measured. D/H versus ¹⁸ O/ ¹⁶ O of the leaf water show a strong enrichment in D and ¹⁸ O compared to irrigation H₂O due to evapotranspiration effects due to the loss of H₂.¹⁶O C4 plants show greater leaf water enrichment compared to C3 plants related to differences in stomatal conductance. All plants show a greater variation in both D/H and ¹⁸O/¹⁶O that appears to be related perhaps to leaf morphology or other factors such as humidity, temperature or light. The leaf water enrichment is also expressed in D/H of individual leaf wax lipids. A further set of experiments using leaves of similar morphology but grown under varying humidity, CO₂, temperature and light conditions are in progress. Preliminary results show that plants grown under low humidity conditions show greater variability in leaf water enrichment than plants grown under high humidity conditions.

Personnel

K. Grice, S. Schouten, S. Wong, H. Williams, G. Farquhar, Y. Zhou, S. Wang

Funding

ARC (QEII)

Collaborators

RSBS Australian National University, Royal Netherlands Institute for Sea Research