Tracing root-felt sodium concentrations under different transpiration rates and salinity levels

Abstract

(1) Monitoring ‘root-felt’ salinity by using rhizoslides as a non-invasive method, (2) Studying how transpiration rate, salinity in irrigation water, and root water uptake affect sodium distribution around single roots, (3) Interpreting experimental results by using simulations with a 3-D root system architecture model coupled with water flow and solute transport models. Tomato plants were grown on rhizoslides under various salinity levels and two transpiration rates: high and low. Daily root images were processed with GIMP and incorporated into a 3-D numerical model. The experiments were simulated with R-SWMS, a 3-dimensional numerical model that simulates water flow and solute transport in soil, into the root and inside root systems. Both experimental and simulation results displayed higher root-felt sodium concentrations compared with the bulk concentrations, and larger accumulation at higher transpiration rate. The simulations illustrated that the root-felt to bulk concentration ratio changed during the experiment depending both on the irrigation water salinity and transpiration rate. Changes in sodium concentrations with transpiration rates are most likely caused by root water uptake and ion exclusion. Simulation results indicate that root-scale process models are required to link root system architecture, environmental, and soil conditions with root-felt salinities.