EGU25-12200, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-12200
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Declining Soil Hydraulic Conductivity Shifts Root Water Uptake from Bulk Soil to the Rhizosphere and Triggers Stomatal Closure
Sara Di Bert1, Pascal Benard2,1, Rong Jia5,1, Fabian Joscha Pascal Wankmüller1, Seren Azad3, Anders Kaestner3, Andrea Nardini4, and Andrea Carminati1
Sara Di Bert et al.
  • 1ETHZ, Institute of Terrestrial Ecosystems, Environmental Systems Science, Zürich, Switzerland (sara.dibert@usys.ethz.ch)
  • 2SLU, Department of Soil and Environment, Uppsala, Sweden
  • 3PSI Center for Neutron and Muon Sciences, Villigen PSI, Switzerland
  • 4Dipartimento di Scienze della Vita, University of Trieste, Trieste, Italy
  • 5State Key Laboratory of Maize Bio–breeding, College of Agronomy and Biotechnology, China Agricultural University, Beijing, China

Soil water availability is a critical factor in determining how plants regulate their water relations, with drying soils imposing hydraulic constraints that affect root water uptake and stomatal behavior. As soils dry, their hydraulic conductivity is reduced, limiting water movement to the roots and ultimately impacting the flow of water within the soil-plant continuum. When root water uptake exceeds the flow rate allowed by the bulk soil, transpiration cannot be sustained for long. In theory, the critical point when root water uptake is no longer matched by soil water flow should be concomitant with a local depletion of water in the rhizosphere. However, such local depletion has never been observed.

In this study, we used a time-series neutron radiography performed at the ICON beamline of the Paul Scherrer Institute (Villigen PSI, Switzerland) to visualize and quantify root water uptake and soil water distribution in maize samples. Seedlings were grown under controlled conditions in rhizoboxes filled with sandy and loamy soils for two weeks, followed by a period of progressive drying. High-resolution imaging revealed a clear shift in water uptake patterns as the soil dried: initially, water was extracted predominantly from the bulk soil, but under drier conditions, uptake increasingly shifted to the rhizosphere. As soil drying progressed, the rate of water uptake from the rhizosphere became insufficient to meet the transpiration demand. The critical point when water uptake shifted from the bulk to the rhizosphere soil occurred at less negative water potentials in sandy soils (-4 to -5 kPa) than in loamy soils (-100 to -300 kPa), reflecting the differences in hydraulic properties between the two soil types.

These results show that under drought conditions, the rhizosphere serves as a primary water source for plants but cannot fully sustain transpiration over time, ultimately leading to stomatal closure and reduced water loss. By providing direct experimental evidence of how soil hydraulic limitations and rhizosphere water dynamics shape plant responses, this study provides new experimental evidence on the key role of rhizosphere water dynamics in regulating plant water use.

How to cite: Di Bert, S., Benard, P., Jia, R., Wankmüller, F. J. P., Azad, S., Kaestner, A., Nardini, A., and Carminati, A.: Declining Soil Hydraulic Conductivity Shifts Root Water Uptake from Bulk Soil to the Rhizosphere and Triggers Stomatal Closure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12200, https://doi.org/10.5194/egusphere-egu25-12200, 2025.