Hydrogen isotopes in plant organic compounds indicate strong shifts in the carbohydrate metabolism of plants over the past century

In contrast to the stable C, N and O isotope composition of plant materials, the hydrogen isotope composition of plant organic compounds has not yet been established as a tool in ecological or biogeochemical research. With the development of new analytical instruments that allow the hydrogen isotope analysis of selected plant compounds there is, however, growing interest to explore the power of hydrogen isotopes as tools for ecological and biogeochemical research. In my talk I will summarize recent work from my lab where we show that the hydrogen isotope composition of lipids and carbohydrates reflect the carbon and energy metabolism in plants: Our experiments revealed that autotrophic and carbon-autonomous plant tissue is ²H depleted while heterotrophic or non-carbon-autonomous tissue is ²H enriched. We were able to identify various biochemical processes during the biosynthesis of plant tissue that contribute to these patterns and can show that these patterns apply for various levels of organization: across plant species (e.g. heterotrophic parasitic plants and their autotrophic hosts), across different organs within an individual plant (e.g. autotrophic leaves vs. heterotrophic roots), and even within a plant organ (e.g. following the transition of a leaf from a carbohydrate sink to a carbohydrate source during ontogeny). As such, the hydrogen isotope composition of plant tissue seems to be a robust proxy for the carbohydrate metabolism in plants and could serve thus as an important new tool in plant ecology, plant breeding, biogeochemistry, and paleo applications. In fact, we investigated a historic collection of grass samples from the famous 150 year old Park Grass Experiment in Rothamsted and were able to show, that the hydrogen isotope composition of grasses has become ²H depleted by about 40 per mil over the past decades. This suggests that global environmental change leads to significant and previously unresolved shifts in the carbohydrate dynamics of plants and that the hydrogen isotope composition of carbohydrates and lipids is a fascinating new tool to identify these changes.

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Invited by Gerhard Gebauer, BayCEER Isotope Biogeochemistry

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