Effect of Transpiration Rate on Na⁺ Distribution at The Root-Soil Interface

When salinity increases beyond a certain threshold, crop yield will decrease at a fixed rate. Salinization in the root zone might cause growth inhibition and yield reduction of crops, especially in arid and semi-arid areas. Thus, predicting salinization and its impact on crops is highly important. Additionally, in roots research today, there is lack in suitable methods to measure processes at the scale of a single root, as most measurements are usually taken from the general root zone. Current models do not consider the impact of transpiration rate on plant salt tolerance, as well as the “root-felt” Na⁺ concentration, although they affect plant water uptake and thus salt accumulation around the roots, consequently influencing the plant’s sensitivity to salinity. Better parameterization of models can help to improve predicting the real effects of salinity on crop growth and yield. For the first time, rhizoslides were used to study how transpiration rate, salinity in irrigation water and plant water uptake affects the Na⁺ distribution around single roots and the hydraulic conductivity of the root system. Root system architecture was retrieved from photos taken during the experiment, enabling to incorporate real root systems into a simulation. Hydraulic conductivity of roots was measured from plants growing in combined treatments of five salinity levels and two transpiration rates. These experimental data were used to parameterize a 3-D root architectural model coupled with a water flow and solute transport models. Both experimental and simulation results displayed higher Na⁺ accumulation at the root-soil interface compared with the bulk, and that this accumulation is larger at higher transpiration rate. These data are being used for model calibration, which is expected to enable the prediction of root water uptake in saline soils for different transpiration demands and different soil water availabilities.