“Climate change presents new challenges regarding water regulation for plants”
Freiburg, 29/05/2026
How exactly do plants regulate their uptake and release of water during drought stress? This is what the new research unit SOPHY, which is funded by the German Research Foundation (DFG), is investigating. Professor Christiane Werner, Professor of Ecosystem Physiology at the University of Freiburg’s Faculty of Environment and Natural Resources, and her colleague Dr Simon Haberstroh are involved. In this interview Werner talks about how through SOPHY researchers can study the interaction and adaptation of plants during drought phases.
Professor Werner, you study the reactions of plants and entire ecosystems to climate change. What exactly is your new research unit investigating?
At the SOPHY Research Unit we want to improve our understanding of how the entire system of water regulation functions across every level – starting with the soil structure, through water uptake into the roots and transportation into the plant via its water transport system, the xylem, right up to regulation in the leaves and the release of water into the atmosphere. In Freiburg we are looking at the interaction between plants in particular, that is, the question of how plant communities use water – competitively or collaboratively.
“At the SOPHY Research Unit we want to improve our understanding of how the entire system of water regulation functions across every level – starting with the soil structure, through water uptake into the roots and transportation into the plant via its water transport system, the xylem, right up to regulation in the leaves and the release of water into the atmosphere. “
Prof. Dr. Christiane Werner
Professor of Ecosystem Physiology, Faculty of Environment and Natural Resources, University of Freiburg
The fact that plants absorb and release water is of course something very fundamental. What is it about this process that particularly interests you?
Climate change brings us new conditions, and that also means new challenges for plants regarding water regulation. On the one hand, drought means there is less water in the soil. And on the other, if the air continues to get hotter and drier, there’ll be far greater uptake by the plants, and evaporation from the leaves leads to greater loss of water. The key question is how plants cope with these challenges in the system as a whole.
So how do you study this?
Among other things, our project works with stable isotopes. They are not radioactive, simply available in the environment, and they can serve us as markers with which we can make the flow of water visible. We give plants water with heavy water isotopes such as deuterium, and then using our equipment we can measure in real time how and when precisely water is absorbed by plants under which specific conditions, how quickly they transport it and release it through their leaves – and of course how neighbouring plants compete with them for water.
You’re researching these mechanisms in the copper beech and small-leaved lime. Why did you choose these two tree species? Both are important tree species for us here, and both could in fact be pushed to their limits in extremely hot summers by climate change. But mainly it’s because they are two types of plant that regulate their water balance differently. One species is more conservative in its use of water, the other consumes more water – if they both grow in competition to one another, different competitive advantages can develop. So we’re especially interested in how the two tree species interact during heat stress.
„Es gibt sogar Effekte, die man als „Drought Memory“ bezeichnet, eine Pflanze erinnert sich also an schon dagewesene Dürren und passt sich an.“
Prof. Dr. Christiane Werner
Professor of Ecosystem Physiology, Faculty of Environment and Natural Resources, University of Freiburg
What new discoveries do you hope to make?
We’re hoping to improve our understanding of the temporal dynamics of water regulation. We’ve already seen that the regulation and interaction changes from when a drought starts until it reaches its extreme. There are even effects known as ‘drought memory’: that is, a plant recalls past droughts and adapts.
So can plants learn from experience?
I’d rather speak of adaptation – the plant responds and adjusts its regulation. These mechanisms differ depending on whether a plant grows together with its own species or with species that use water in other ways. Precisely how these mechanisms function is the key question that we are tackling at the research unit in Freiburg.
Can the results be applied with regard to climate change?
Definitely! For example, we’re also measuring these processes in forests. We can’t control the conditions there quite so well, but we can still measure the reactions of the plants directly in their natural environment. For instance, we’ve already had exciting results from the interaction of spruce and beech in the competition for water, which mainly benefits the beech. In the measuring equipment that we are going to use in the new research unit, we can modify different environmental conditions better and more precisely than in the forest. In this way we can identify what is the trigger and what the effect of such regulation. If we can understand where the tipping points are for specific plants, the limits of water regulation, but also the key parameters throughout the process of transporting water through the plant, then this is in the end also relevant to forestry and to potential responses to climate change.
SOPHY Research Unit
The research unit Soil-plant hydraulics impacting transpiration and plant growth in response to drought (SOPHY) is being funded by the German Research Foundation (DFG) together with the Swiss National Fund (SNF) for an initial four years; it launches in autumn 2026. The speaker at the research unit is Professor Mutez Ali Ahmed of the TU Munich, while Professor Christiane Werner and Dr Simon Haberstroh of the Faculty of Environment and Natural Resources are involved on behalf of the University of Freiburg. The research unit also includes researchers from the Universities of Ulm and Bonn, TU Dresden, the Forschungszentrum Jülich, ETH Zürich, Purdue University in West Lafayette (USA) and Macquarie University in Sydney (Australia).
A special issue of the journal Plant Biology on the effects of drought and its consequences for plants and ecosystems
Together with her colleagues Professor Christiane Werner published a special issue of the journal Plant Biology in April 2026. The special issue titled ‘Impacts of droughts and drought legacies on plants and ecosystems’ looks at among other things what are known as ‘compound droughts’, that is, the interaction of drought and heat, and their influence on ecosystems.