Simulation of climate-change scenariosLabelling-experiment to investigate the carbon cycle in Elbe marsh soils

22 September 2025, by RTG 2530

Photo: UHH/RTG2530/Lork

Climate Change Marsh Mesocosm Facility, an experimental site at the University of Hamburg.

Researchers of the RTG 2530 have developed a labelling experiment to investigate the effects of climate change on the carbon cycle in marsh ecosystems. Specifically, they are investigating how carbon flows are affected by rising temperatures and increasing salinity, the roles that plants and microorganisms play in this process, and the extent to which greenhouse gases are emitted or carbon is stored in the soil.

The experiment started in autumn 2024, when scientists from the RTG 2530 took blocks of soil covered with plants from the Elbe marsh near Hollerwettern-Wewelsfleth. They brought them to the Institute of Plant Sciences and Microbiology (IPM) in Klein Flottbek and set them up in the Climate Change Marsh Mesocosm Facility, an experimental site at the University of Hamburg. Once the soil had settled, the experiments began in March 2025. The material was exposed to specific environmental conditions: temperature increases based on climate scenarios, as used in the reports of the Intergovernmental Panel on Climate Change (IPCC), were generated by infrared radiation and heating elements in the soil, while an increase in salinity simulated sea level rise and storm surges.

This was followed in August 2025 by isotope labelling: on four days (22, 25, 26, and 27 August 2025), the soil blocks covered with marsh plants were fumigated with ¹³C-labelled CO₂ under plastic covers for two hours. Plants absorb this gas during photosynthesis and convert it into sugar and other organic compounds, which are either used for plant growth or released into the soil via the roots as exudates.

UHH/RTG2530/Lork

The advantage of this method is that the labelled CO₂ leaves a ¹³C signature, which can be used to track where the carbon is stored in the plants, how microorganisms use the exudates, the stability of the carbon in the soil, and how much of it escapes back into the atmosphere as a greenhouse gas. When combined with climate simulations, this leads to model calculations showing how the carbon cycle might change in the future.

UHH/RTG2530/Lork

When asked about the challenges and successes the experiment has revealed so far, Dr Joscha Becker, scientific director of the experiment, responds: "One of the biggest challenges was to combine the many different scientific objectives and research questions into a single, common experimental design. The fact that we have managed to carry out this unique experiment successfully is already a significant achievement. Now we are eagerly awaiting the results of the laboratory analyses, which should provide further valuable insights into the complex interrelationships."

UHH/RTG2530/Lork

The final sampling will take place in early October 2025, when plants, soil cores, and soil microorganisms will be collected. These samples will then be analysed in the laboratories of plant ecology, soil science, microbiology, and biotechnology at the University of Hamburg.