Environmental Conservation

CO2 and Global Warming: How Soils and Plants Challenge Future Droughts

Grassland experiment analyzing soil hydrology under climate change conditions

Pilot plant in Styria. Aerial view of the ClimGrass plant in Styria, where a temperate grassland is exposed to individual and combined atmospheric warming (+3°C) and CO2 enrichment (+300 ppm) as well as recurrent drought. Copyright: Lisa Capponi

What will the future of our soils – and thus also the availability of water – look like under the influence of imminent climatic changes? An international study led by Jesse Radolinski and Michael Bahn from the Institute of Ecology at the University of Innsbruck shows how drought, warming and increased CO₂ concentrations in the atmosphere change the hydrological balance in the soil and challenge the resilience of ecosystems. The results were published in the journal Science.

Years of experimentation
Experiments were carried out under different conditions on the test plots.
Copyright: Andreas Schaumberger

Grasslands cover almost 40 percent of the earth’s surface and play an important role in the global water cycle. Nevertheless, there is still a lack of understanding of how climate change affects these vital ecosystems. A new study, conducted as part of an international project funded by the Austrian Academy of Sciences and led by Michael Bahn from the Functional Ecology research group at the University of Innsbruck , now provides new insights into the future of grassland ecosystems. The results of this year-long study illustrate how drought, increased temperatures and rising CO₂ concentrations affect the availability of soil water and plant water use. “We simulated the changes expected in future climate scenarios of three key factors: warming, increased atmospheric CO₂ concentrations and drought. We investigated the effects both individually and in different combinations,” explains Michael Bahn. Using rainwater labeled with stable isotopes, the team was able to analyze in detail the movement and storage of water in the pore space of the soil and during evaporation after the drought ended.

Can Increased CO2 Levels Have Short-Term Positive Effects

Under increased CO₂ concentrations, the root space of the plants remains moister because the plants use water more efficiently. Heat, on the other hand, leads to a general loss of moisture in the soil. If drought also occurs repeatedly in a future warmer climate, there will be strong changes in soil properties. “In these scenarios, the water in the soil is mixed less well, as it flows mainly through the large, fast-draining pores and penetrates less strongly into the smaller, slow-draining pores. The older water also adheres longer there,” Jesse Radolinski explains. This impairs hydrological connectivity, which is essential for the water availability of plants. The researchers emphasize that this restriction of water flows in the soil has far-reaching consequences for the function and resilience of grassland ecosystems. Plants are forced to use water more sparingly, which could limit their ability to grow and regenerate in the long term. “At the same time, however, our study also shows that increased CO₂ levels in the atmosphere can have short-term positive effects, such as a faster recovery after droughts. However, these effects are overshadowed by the negative effects of increasing warming and drought on soil properties,” says Bahn.

Unique Experiment Setting on Future Climate Implications

Aerial photograph
View from above of the test site in Styria.
Copyright: Lisa Capponi

“Our experiment is unique because we have been able to experimentally simulate the conditions of a future climate since 2014 and thus analyze the longer-term effects,” Bahn emphasizes. The researchers used a unique experimental facility that they designed at the agricultural research institute in Raumberg-Gumpenstein in Styria. It includes 54 trial plots with radiant heaters and CO₂ fumigation systems as well as automated roofs that can shield the rain. This made it possible to simulate a number of realistic climate scenarios and to study the interactions between soil water and plants in detail.

Complex Relationship between Soil and Plants Revealed

The main finding of the study is that the hydrological connectivity in the pore system of the soil is permanently disturbed by recurring drought phases, which has a particularly strong effect in a warmer climate with increased CO2. “Previously, it was assumed that soil water would be well mixed when it rains, but our results show that this mixing will be severely limited after repeated droughts in a future climate. This has significant implications for water use by plants and ecosystem dynamics,” explains Radolinski.
“The study shows that the interactions between soil and plants could be much more complex than previously thought. This has a significant impact on the ability of ecosystems to survive and recover from droughts,” Bahn summarizes. The results of the study once again underline the need to develop strategies to strengthen the resilience of ecosystems to climate change and to advance global efforts in climate protection.

Contact
Michael Bahn
Institute of Ecology
University of Innsbruck
Phone: +43 512 507 51360
E-Mail: michael.bahn@uibk.ac.at

Original Publication
Jesse Radolinski, Matevz Vremec, Herbert Wachter, Steffen Birk, Nicolas Brüggemann, Markus Herndl, Ansgar Kahmen, Daniel B. Nelson, Angelika Kübert, Andreas Schaumberger, Christine Stumpp, Maud Tissink, Christiane Werner, Michael Bahn
Journal: Science
Article Title: Drought in a warmer, CO2-rich climate restricts grassland water use and soil water mixing
Article Publication Date: 16 Jan 2025
DOI: 10.1126/science.ado0734

Media Contact
Melanie Bartos
Public Relations Office
University of Innsbruck
Phone Number: +43 512 507 32021
Mobile Number: +43 676 8725 32021
E-Mail: melanie.bartos@uibk.ac.at

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