PP11B-2233
Do Interspecific Differences in the Stable Hydrogen Isotopic Composition of n-Alkanes Reflect Variation in Plant Water Sources or in Biosynthetic Fractionation?

Monday, 14 December 2015
Poster Hall (Moscone South)
Jennifer E Johnson1, Brett James Tipple2, James R Ehleringer3, Julio L Betancourt4 and Russell K Monson1, (1)University of Arizona, Tucson, AZ, United States, (2)University of Utah, Department of Biology, Salt Lake City, UT, United States, (3)University of Utah, Salt Lake City, UT, United States, (4)U.S. Geological Survey, Reston, VA, United States
Abstract:
Normal alkanes (n-alkanes) are long-chain fatty acids that are a component of the leaf cuticle of all terrestrial plants. Since the hydrogen in the n-alkanes is derived from the hydrogen in plants’ water sources and is non-exchangeable, the stable hydrogen isotopic composition (δD) of the n-alkanes provides information about the δD of environmental water. At present, it is unclear whether a single biosynthetic fractionation factor can be used to reconstruct the δD of environmental water from the δD of n-alkanes derived from different plant species. To address this question, we studied the translation of the δD signal from environmental water into n-alkanes in a diverse plant community at Tumamoc Hill, Arizona, USA. Over the course of one annual cycle, we monitored δD of atmospheric water vapor, precipitation, soil water, xylem water, leaf water, and n-alkanes. We found that n-alkane δD varied substantially between species that were sampled concurrently, but that the observed range of variation was quantitatively consistent with the predictions of a Craig-Gordon-type model parameterized with a single biosynthetic fractionation factor. These findings indicate that the variability of n-alkane δD between co-occurring species could be primarily attributable to interspecific differences in water sources, rather than interspecific differences in the biosynthetic fractionation factor. Controlled experiments are needed to evaluate whether n-alkane biosynthesis is in fact adequately described by a single biosynthetic fractionation factor across species.