PhD project offered by the IMPRS-gBGC in Jan 2026

Water use strategies of global tree-grass savannas during drying and rewetting soils

Sung-Ching Lee , Bryn Morgan , Anke Hildebrandt , Markus Reichstein

Project description

Responses of vegetation to water availability greatly impact the global water budget and influence carbon and energy fluxes. But water use strategies vary a lot among different plants, with some adopting aggressive water use, risking hydraulic damage, while others conserve moisture in the soil for longer. These strategies are influenced by ecological and hydroclimatic conditions, affecting ecosystem resilience to drought. Understanding these adaptive responses is crucial for improving projections of future water and carbon budgets. It has been found that water use becomes more conservative as tree cover increases from grasslands to savannas to forests. Water-use strategies in savannas reflect their mixed tree-grass composition, behaving in between grassland and forest ecosystems (Morgan et al., 2025). However, climate change will have significant effects on structure (tree–grass ratio) of these savanna ecosystems, and consequently their functions. Furthermore, these ecosystems mostly exist in arid and semi-arid regions where their functions are largely pulse-driven, making them the most important contributor to the interannual variability of global land carbon sinks. Therefore, these ecosystems are facing rapid swings in productivity and shifts in fire regimes.
The overarching goal of this PhD project is to improve our understanding sensitivity of vegetation of tree-grass savannas to water stress and underlying mechanisms. Specifically, the PhD will leverage our long-term sites and use the global flux network and its latest data system to 1) assess what are the patterns of water-use strategies across years, 2) identify what are the drivers of observed dynamics and how do extremes alter it, and 3) model responses of tree-grass savannas to increasing ecological and hydroclimatic demand. The prospective PhD student will also be encouraged to explore their own innovative approaches within this proposed framework.

Working group

The successful candidate will work in the Biogeochemical Integration department at the Max Planck Institute for Biogeochemistry and will also be affiliated with the Friedrich Schiller University, Jena. The working group, Eco-Meteorology, offers long-standing expertise and experience in the various fields relevant to this project. This project will have close interactions with the Department of Civil and Environmental Engineering at Massachusetts Institute of Technology. For further information, please contact Sung-Ching Lee

Requirements

Applications to the IMPRS-gBGC are open to well-motivated and highly-qualified students from all countries. Prerequisites for this PhD project are:

Master's degree in ecohydrology, environmental science, earth system science, biogeosciences, climate science or related fields.
Strong background in eddy-covariance, soil-plant-atmosphere processes, or water-carbon dynamics.
Proficiency in a modern programming language (e.g., Python, R, Julia) and experience in handling large dataset and data integration.
Broad interest in process-based or physics-guided machine learning models.
Fluency in spoken and written English.
Willingness to work in an interdisciplinary environment with geoscientists and computational scientists

The Max Planck Society (MPS) strives for gender equality and diversity. The MPS aims to increase the proportion of women in areas where they are underrepresented. Women are therefore explicitly encouraged to apply. We welcome applications from all fields. The MPS has set itself the goal of employing more severely disabled people. Applications from severely disabled persons are expressly encouraged.

References

Morgan, B. E., et al. (2025). Ecological and hydroclimatic determinants of vegetation water- use strategies. Nature Ecology & Evolution, 1-9.

Nadolski, L., et al. (2025). Altered seasonal sensitivity of net ecosystem exchange to controls driven by nutrient balances in a semi-arid savanna. Biogeosciences, 22(12), 2935-2958.

Hutley, L. B., et al. (2022). Gross primary productivity and water use efficiency are increasing in a high rainfall tropical savanna. Global Change Biology, 28(7), 2360-2380.