Exploring osmotic stress and differences between soil–root interface and bulk salinities

Design of efficient water irrigation strategies with a combination of highquality water and saline water relies on accurate prediction of root water uptake. Macroscopic models are usually used to predict root water uptake at the field scale. However, they miss proper representation of stress processes at the plant scale. A fully mechanistic three-dimensional model was used to investigate the effect of root length density (RLD), transpiration rate and dynamics, potential leaching fraction (LF), and irrigation frequency and salinity on osmotic stress and gradients developed between the soil– root interface and the bulk soil. For the same LF and salinity level of the irrigation water, osmotic stress was larger at lower RLDs and higher transpiration rates. Roots were also more stressed when a sinusoidal transpiration boundary condition was considered. The variability of macroscopic parameters calculated for the simulated data show that macroscopic functions need to take into account RLD and transpiration rate to adequately predict osmotic stress. Finally, small salt concentration gradients were observed in this single-root study where root density was assumed constant with depth. However, future work requires checking salt concentration gradients at the scale of a whole plant, where this assumption does not apply.