Influence of salinity on transport of nitrates and potassium by means of the xylem sap content between roots and shoots in young tomato plants

Salinity is well known to reduce plant growth and yield by reducing water availability; it does so by interfering with both nutrient uptake and translocation. The objective was to determine the nitrate and potassium contents in xylem sap and the root-shoot transportation of both as a function of the salinity of the nutritional solution provided. We compared NO₃- and K⁺contents and flux in xylem sap collected from cut stems of tomato seedlings, based on electric conductivity (EC) tests among five nutrition solutionsfor soilless crops ranging from medium to high salinity. The EC was 2.2, 3.5, 4.5, 6 and 12 dS m^-1. The concentration of nitrates and potassium in the xylem sap remained constant, while the external concentration in the rhizosphere varied greatly. Notwithstanding, the xylematic flux was strongly affected by the salinity of the nutritional solution: at maximum salinity, EC reached 3.5 dS m^-1; at minimum, EC was 12 dS m^-1. For similar reasons, the longest NO₃^- and K⁺ transportation distance between root and shoot was achieved when the EC read 3.5 dS m^-1, but was reduced by up to 80% when EC was 12 dS m^-1.