Hydrogen isotopes in plant-derived organic compounds as new tool to identify changes in the carbon metabolism of plants and ecosystems during the anthropocene

Project Information

HYDROCARB

Grant agreement ID: 724750

DOI

10.3030/724750

Project closed

EC signature date 15 December 2016

Start date 1 November 2017

End date 31 October 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 999 941,00

EU contribution

€ 1 999 941,00

Coordinated by

UNIVERSITAT BASEL
Switzerland

Periodic Reporting for period 4 - HYDROCARB (Hydrogen isotopes in plant-derived organic compounds as new tool to identify changes in the carbon metabolism of plants and ecosystems during the anthropocene)

Reporting period: 2022-05-01 to 2023-10-31

Summary of the context and overall objectives of the project

Understanding how plants and ecosystems respond to global environmental changes is a key challenge in the biological sciences. Biological archives, such as tree rings or herbarium specimens in historical botanical collections are critical tools to address this challenge. This is, because the analysis of the stable isotopes in archived plant material allows researchers to identify how plant physiological processes have responded to environmental changes over the past decades. Until now, these analyses have mainly employed the stable isotopes ratios of carbon, oxygen, and nitrogen. In his new project HYDROCARB, will establish the analysis of hydrogen isotopes in botanical archives to obtain new information on environmentally induced changes in plants’ carbon metabolism.
The carbon metabolism of a plant has a fundamental influence on plant growth. It has therefore a key influence on yields in the agriculture and forestry but also on the global carbon cycle and the global climate. Kahmen and his team seek to use the novel hydrogen isotope analysis of archived plant materials to better understand how the carbon metabolism in plants and thus plant growth and the global carbon cycle have responded to changes in the global environment over the past 150 years.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

HYDROCARB made substantial progress in the understanding of hydrogen isotopes in plants and their application to infer effects of global environmental change on plant metabolism. In a range of experiments we confirmed the main hypothesis of HYDROCARB, namely that plant δ2H values are linked to the plant's carbon metabolism but also showed that these effects are more strongly expressed in carbohydrates than in lipids. The experimental results advanced semi-mechanistic models for the interpretation of cellulose and lipid δ2H values. However, additional experiments will be necessary for a robust interpretation of cellulose and lipid δ2H values. HYDROCARB yet applied the model in interpreting δ2H values of archived plant materials from the famous Rothamsted Park Grass Experiment in an initial test. The data show that plant δ2H values increased with time but only in fertilized plots, suggesting an important elevated CO2 vs. nutrient interaction in driving plant metabolism.

The expertise that the HYDROCARB team developed over the years opened up opportunities for additional, originally unplanned investigations and collaborations with leading research labs around the world:
1) Complementing the experiments of WP2 we actively collaborated with the world-wide unique ecosystem global change experiment ClimGrassHydro in Austria. This experiment manipulated growing season temperature, soil moisture and atmospheric CO2 in an established montage grassland in Austria. Particularly relevant for HYDROCARB was the discovery that preferential flow of water in rewetted soil was strongly influenced by environmental treatments, with implications for source water δ2H values of plants (Radolinski et al. Science in review).
2) We also collaborated with a European consortium using oxygen isotopes from tree rings for the reconstruction of past hydroclimates. The collaboration resulted in a unique dataset that revealed that VPD (i.e. water demand of the atmosphere) is higher today in Europe than at any given point in time in the past 400 years (Treydte et al. 2024, Nature Geosciences).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

HYDROCARB produced several high-impact outcomes, some of them not anticipated at the start of the project. Uncertainty in HYDROCARB data forced us to explore the global isotopes in precipitation database (GNIP) with statistical methods, including machine learning algorithms, to create such a product. The outcome of this work is the PISO.AI model that is feely available online (https://isotope.bot.unibas.ch/PisoAI/) and can simulate back to 1950 monthly precipitation δ2H and δ18O values for any given location in Europe. The development of this model advanced the field significantly, because it allows for the first time to base the interpretation of δ2H and δ18O values in plants on precise and accurate background precipitation δ2H and δ18O values. This has implications for the application of these signals in plant ecology, paleoclimatology and forensic sciences.

The combination of papers that we published from the HYDROCARB project addressing the biochemical fractionation factors that determine the hydrogen isotope composition of plants and to establish the link between environmental forcing, a plant's carbohydrate metabolism, biochemical pathways and the δ2H values of plant-derived organic compounds can also be regarded significant achievements. These studies have much advanced the mechanistic understanding of what drives the hydrogen isotope composition of plant materials and what physiological processes they reflect. We are preparing a comprehensive review paper for the journal New Phytologist as a key outcome of HYDROCARB that will summarize this information for the scientific community, We expect this review to be highly cited with a high impact on the field.

With the many experiments performed in the context of HYDROCARB, the team build extensive expertise on the δ2H and δ18O values of plant materials and how to interpret them. This led to unplanned discussions how to best interpret tree ring δ2H and δ18O values and the exploitation of an extensive European-wide tree ring oxygen isotope data base. The δ18O data in this database revealed that the atmospheric vapor pressure has been increasing in Europe over the past decades due to atmospheric temperature increases and that atmospheric drying is the strongest today since the last 400 years (Treydte et al. 2024, Nature Geosciences). A dry atmosphere has severe consequences for the water relations of ecosystems as it drives evaportanspiration. As such, the paper that HYDRICARB significantly contributed to, stresses one of the key climate change agents for European Ecosystems and puts the magnitude of this change into a historical perspective.

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