Seasonal variations in compound-specific leaf-wax lipid δD values and their relationship to environmental factors and plant physiological processes
Abstract
Lipids are present in high concentrations in the leaf waxes of deciduous plants and are the final products of plant biosynthesis. Their hydrogen isotopic composition (δD) should therefore provide a time- integrated value of the leaf water used for biosynthesis and in turn the environmental and physiological factors determining leaf water enrichment. Due to the stability of lipids, their stable isotopic composition in soils and sediments could become a powerful tool to asses (paleo)hydrologic conditions. However, the relative importances of plant physiology and climatic influences as well as the timeframe over which the lipid δD value integrates these factors have not been investigated systematically. Here we explore how changes in environmental parameters and plant physiological processes over a growing season are recorded in compound-specific hydrogen isotope ratios of individual leaf-wax lipids. We sampled soil water, leaf water at dawn and midday, water vapor for hydrogen isotopic analysis, leaves for lipid analysis and recorded a number of environmental parameters (temperature, relative humidity, vapor pressure deficit among others) and plant physiological data (stomatal conductance, transpiration, photosynthetic rate) weekly over the two month growing season of wheat grass. We analyze the relative importance of plant physiological processes and environmental factors in determining leaf water enrichment and the leaf wax lipid isotopic composition. The isotopic composition of soil water and leaf water at dawn showed similar trends and increased over the growing season with short-term variations of about 40‰. Leaf wax lipid δD values varied only on the order of 20‰ over the growing season following a similar trend as soil water and leaf water at dawn. We observe a 20‰ decrease in lipid δD values only a week after a significant 40‰ decrease in the soil and leaf water isotopic composition, due to a strong rain event. These results suggest, that leaf-wax lipids are produced during the whole growing season and record the leaf water isotopic signal integrated over a timeframe on the order of a week. We observe stronger correlations of environmental conditions at dawn with the lipid δD values compared to midday conditions, suggesting more of a climatic background signal is recorded in the lipids removing the midday extremes. Systematic studies like the one presented here are essential, when interpreting variations in leaf-wax lipid δD values in soils and sediments as records of (paleo)ecosystem hydrology.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.B22A..04S
- Keywords:
-
- 0476 Plant ecology (1851);
- 1705 Biogeosciences;
- 3344 Paleoclimatology (0473;
- 4900);
- 4870 Stable isotopes (0454;
- 1041)