How are the driving forces of root water uptake altered in crop plants under water deficit?

In vascular plants, water moves along decreasing pressure (Ψp) or total water potential (Ψtot) gradients, which is consistent with the second law of thermodynamics. However, several studies report water flowing along increasing water potential gradient across roots. The integration of micro-hydrology modeling with cell solute mapping data has led to the proposition that solute concentration gradients across living cells may serve as a driving force, thereby contributing to a more comprehensive understanding of the current paradigm of water flow across roots. This gradient of osmotic potential (Ψo) may act as an active water pump. To investigate this complementary mechanism experimentally, we performed experiments to investigate root water uptake in maize and tomato plants under both control and water deficit conditions. We measured soil matric potential (Ψsoil), leaf water potential (Ψleaf) and transpiration continuously. It was also measured that of soil Ψo, root hydraulic conductivity, root cell Ψo and xylem Ψo. Root segments where radial water uptake presenting were sampled, and ions were mapped in root cross-sections with Laser Ablation Inductively-coupled plasma mass spectrometry. Our results showed that root bulk Ψo decreased rather than xylem Ψo in maize and tomato plants, grown in soil and hydroponic, respectively, under water deficit treatments in comparison to the control treatments. Preliminary analysis suggests that lower xylem Ψtot was not enough to explain what allows the inflow of water from the soil Ψtot in maize plants under water deficit conditions. In conclusion, our results indicate that osmotic adjustment in root cells plays an important role for plants responding to water deficit treatment and possibly radial water uptake. An inverse-modelling will be performed to simulate transpiration, and this will allow us to compare the observed and simulated transpiration. Finally, the results will tell us if there is a missing driving force for root water uptake.

Affiliations

UCLouvainSST/ELI/ELIA - Agronomy

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Ding, L., Degand, T., D’Agostino, M., Thiébaut, N., Kolawole, M., Dagbert, T., Heymans, A., Couvreur, V., & et al. (2025). How are the driving forces of root water uptake altered in crop plants under water deficit? Rhizosphere 6: Rooting for Earth, Edimburgh. https://hdl.handle.net/2078.5/271076