FOR 5820:  Soil-plant hydraulics impacting transpiration and plant growth in response to drought [SOPHY]

• Subject Area: Agriculture, Forestry and Veterinary Medicine ; Biology
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538902328

Evapotranspiration recycles over half of all terrestrial precipitation, making it a vital process for life on earth. With rising temperatures and changes in rainfall patterns due to global climate change, plants are more frequently and intensively exposed to a dry atmosphere and soil water deficits. These conditions of drought stress pose various challenges for plant growth, both in agriculture and natural ecosystems worldwide, with consequences for food security and problems such as large-scale tree mortality. Yet, one of the evolutionary key-innovations of vascular plants to drought stress is their capacity to control gas exchange by stomata. Based on a parsimonious model that assumes that stomatal regulation during drought depends on the relation between transpiration rate and leaf water potential, it has recently been demonstrated that limits to transpiration by soil water thresholds can be predicted at a global scale from small-scale estimations of the water status in the soil-plant-atmosphere continuum. A key hypothesis is that plants are able to regulate transpiration rates under increasing levels of drought in such a way that the relation between transpiration and leaf water potential remains largely linear. How exactly plants achieve this hydraulic linearity mechanistically is unclear and requires simultaneous measurements of key environmental variables, the plant water status, and various morphological, anatomical, and eco-physiological traits. This interdisciplinary research unit aims to achieve a mechanistic understanding of how angiosperms control water transport across the entire soil-plant system, including the soil, roots, xylem tissue, leaves, and stomata. In addition, this project intents to develop a predictive model of the transpiration rate in response to soil drying across soil types, climatic conditions, and different species. We expect that the water status of the rhizosphere, atmosphere, and the hydraulic plant system are coordinated on short- and long-term time scales to maintain a constant ratio between transpiration rate and the water potential gradient from soil to leaf, while reducing the risk of irreversible drought damage. This hydraulic linearity hypothesis implies that the leaf water potentials at which stomata close depend on belowground water supply in the soil and roots, and on the aboveground atmospheric water demand. The research questions proposed require a highly interdisciplinary approach of soil physicists, plant physiologists, morphologists, and ecohydrologists, with experience in lab and field measurements and modelling. The overall gain in knowledge aimed for in this project is not only relevant to address longstanding, fundamental questions regarding plant water use regulation under drought, but has also significant societal relevance given current and future concerns about climate change.

• DFG Programme: Research Units
• International Connection: Switzerland, USA

Projects

• Coordination Funds (Applicant Ahmed, Mutez Ali )
• SP01: Soil hydraulic constraints on root water uptake and root-rhizosphere adaptations (Applicant Ahmed, Mutez Ali )
• SP02: Plasticity of cell-to-cell and apoplastic water pathways in roots and leaves of maize in response to water deficit in soils (Applicants Bienert, Gerd Patrick ;  Schreiber, Lukas )
• SP03: ABA dynamics in angiosperm leaves control long-distance water transport via stomata (Applicant Jansen, Steven )
• SP04: Relations between transpiration, soil water potential, and leaf water potential at the crop stand scale. (Applicant Vanderborght, Jan )
• SP05: Whole-tree hydraulic performance in two temperate broadleaved species differing in stomatal behaviour (Applicant Schuldt, Bernhard )
• SP06: Tracing regulation of root water uptake depth and (evapo)-transpiration in response to plant-plant interaction of European beech and small-leaved lime (Applicants Haberstroh, Simon ;  Werner, Christiane )
• ZP Central project – Central research platforms and modelling approaches (Applicants Ahmed, Mutez Ali ;  Schuldt, Bernhard ;  Vanderborght, Jan ;  Werner, Christiane )

• Spokesperson: Professor Dr. Mutez Ali Ahmed