PhD project offered by the IMPRS-gBGC in Jan 2026

Reaching deeper – exploring optimal root water uptake strategies at the individual and ecosystem scale

Anke Hildebrandt , Manon Sabot , Christiane Werner , Bernhard Schuldt

Project description

As plants take up carbon through their stomates, they inevitably lose water, which must be taken up from the soil and transported to the leaves. Especially during water limiting conditions, maintaining the functioning of this transport path is crucial for sustaining productivity and eventually survival. Recently Carminati and Javaux (2020) proposed that the loss of soil hydraulic conductivity is the main driver of stomatal control in plants. More specifically, stomata should operate in such a way as to avoid non-linear loss of soil hydraulic conductivity as the soil around the roots dries out. So far these propositions have not yet considered how different rooting depth would affect stomatal control. Rooting depths vary between biomes depending on the climate experienced, but especially depending on typical water deficits and seasonality. At the same time, rooting depth is considered a more or less static species trait and, although the location of root uptake can shift with some flexibility along a plant's root system, species-specific uptake strategies coexist within the same climate. Brum et al. (2019) discovered that coexisting trees in the seasonal Amazonian forest belonged to different hydrological niches, in which rooting depth was coordinated with stress tolerance and light access. Although deep roots can be crucial for reaching water in deeper, potentially moister soil layers during droughts, the relationship between species-specific drought responses and root water uptake depth is not well understood. This is partly due to the high heterogeneity of soil water potentials in drying soils, the fast dynamics in root water uptake depths, and long-term memory effects that differ between deeper and shallower soil and lack of dedicated observations.

This PhD project aims to address this issue by taking a thermodynamic approach to the soil-plant-atmosphere system (Hildebrandt et al., 2016), which can be applied to observations and models alike, and allows evaluating both spatial and temporal variation of root water uptake. Furthermore, the project is embedded in a research consortium that provides access to a comprehensive observational setup, including the measurement of all essential hydraulic variables along the soil-plant-atmosphere continuum in both mesocosms and in the field and stable isotope sensing for water uptake sourcing. This provides a unique opportunity to evaluate how soil exploration for water can be optimised at the individual and ecosystem levels, and how these levels adapt (or not) in shifting environmental conditions. The project will apply thermodynamic diagnostics of potentials along the transpirational flow path both based on the observations and process models of the root system up to the root collar. The project can be adapted to incorporate the specific interests of the PhD researcher, allowing them to set an individual focus for their thesis.

Working group

The successful candidate will work with the Chair or Terrestrial Ecohydrology at the Friedrich Schiller University Jena. The project is embedded in an interdisciplinary research consortium comprising experts from both soil and plant sciences investigating together which strategies and mechanisms enable plants to remain within a favourable transpiration regime in water-limiting conditions. Together they cover a wide range of processes, ranging from the hormone signalling to species interactions, providing excellent opportunities to develop a holistic understanding of plant water relations alongside the other PhD researchers and experts within the consortium and to make unique contributions. The collaboration encompasses the following institutions

Max Planck Institute of Biogeochemistry
University of Freiburg
Technical University of Dresden
Forschungszentrum Juelich
University of Bayreuth
Technical University of Munich
Swiss Federal Institute of Technology Zurich (ETHZ)

The ideal candidate

holds a Master's degree in (geo-)ecology, plant biology, soil science, hydrology, environmental science, geosciences, physics, or other disciplines related to environmental
has experience with soil hydraulic measurements in the field and lab
has programming skills (such as IDL, Matlab, R, Python or Julia) and process modelling of plant water relations, soil or groundwater hydrology
is intrigued with gaining processes understanding at the soil-plant-atmosphere interface from a physics perspective
has excellent oral and written communication skills in English, knowledge of German is an asset

References

Brum, M., Vadeboncoeur, M. A., Ivanov, V., Asbjornsen, H., Saleska, S., Alves, L. F., Penha, D., Dias, J. D., Aragão, L. E. O. C., Barros, F., Bittencourt, P., Pereira, L., & Oliveira, R. S. (2019). Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest. Journal of Ecology, 107(June 2018), 318–333. https://doi.org/10.1111/1365-2745.13022

Carminati, A., & Javaux, M. (2020). Soil Rather Than Xylem Vulnerability Controls Stomatal Response to Drought. Trends in Plant Science, 25(9), 868–880. https://doi.org/10.1016/j.tplants.2020.04.003

Garrigues, E., Doussan, C., & Pierret, A. (2006). Water Uptake by Plant Roots: I – Formation and Propagation of a Water Extraction Front in Mature Root Systems as Evidenced by 2D Light Transmission Imaging. Plant and Soil, 283(1–2), 83–98. https://doi.org/10.1007/s11104-004-7903-0

Hildebrandt, A., Kleidon, A., & Bechmann, M. (2016). A thermodynamic formulation of root water uptake. Hydrology and Earth System Sciences, 20(8), 3441–3454. https://doi.org/10.5194/hess-20-3441-2016

Root water uptake, shown in white, shifting quickly downward along the mature root network of a lupin over a 12-hour period (left) uptake over the first two hours (right) uptake over the following time slices of four hours each. From Garrigues et al., (2006)