Soil hydraulic constraints on root water uptake and root-rhizosphere adaptations

• Applicant: Professor Dr. Mutez Ali Ahmed
• Subject Area: Soil Sciences
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538902328

Plants are subject to varying water demand from the atmosphere and varying water supply from the soil. To adapt to such a dynamic environment, plants need to build an efficient and safe hydraulic system that enable them to maintain growth and at the same time ensure a sustainable water cost, which is reasonable to be expressed in terms of water potential. We hypothesize that an optimal water use regulation is achieved when plants approach the onset of non-linearity in the relation between transpiration rate and leaf water potential. Beyond this point, when a slight increase in gas-exchange with the atmosphere implies a disproportional drop in leaf water potential, transpiring (and growing) becomes increasingly inefficient. This hypothesis that plants remain in a linear relationship between water flow and water potential requires a coordination between stomatal closure (regulating the water flow together with the atmospheric demand) and hydraulic conductances (determining the gradient in water potential required to drive the water flow). We postulate that the hydraulic conductance of the soil and its interface with the roots (the so-called rhizosphere) play a central role in regulating the whole soil-plant hydraulic conductance, particularly in coarse textured-soils (such as sandy soils). Therefore, in this interdisciplinary proposal we investigate the hydraulic properties of the soil and its interface with the roots, together with their impact on the whole plant conductance and on stomatal downregulation of gas exchange. We planned a number of complementary experiments from the single root to the whole soil-plant scale to image: 1) the root-soil contact (at what soil water potential do roots shrink), 2) the water dynamics in the rhizosphere relative to the bulk soil (at what water potential does the soil start to limit the flow to the root), and 3) where along the root system water is taken up from the soil. To this end we will employ synchrotron based x-ray tomography and neutron radiography. In addition, we will conduct experiments in which soil and leaf water potentials and transpiration rate will be monitored during a dry-down. The information from these complementary experiments will shed light on the coordination between leaf, root and soil hydraulics and the hydraulic mechanisms how plants cope with and adjust to water limitations.

• DFG Programme: Research Units
• Subproject of: FOR 5820: Soil-plant hydraulics impacting transpiration and plant growth in response to drought [SOPHY]
• International Connection: Switzerland
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Co-Investigator: Dr. Tina Köhler
• Cooperation Partner: Professor Dr. Andrea Carminati