850 professional

The ISO 10304–1 method¹² was used to quantify the concentration of NO₃⁻ and Cl⁻, including homogeneity and stability measurements. Specifically, an ion chromatograph (IC) (850 Professional, Metrohm, Switzerland) with a conductivity detector and polyvinyl alcohol/quaternary ammonium column (Metrosep A Supp 5-150/4.0, Metrohm, Switzerland) was used. Details about operating conditions used in the IC system are shown in Supplementary Table S3. Standard reference materials—SRM 3185 and SRM 3182—provided metrological traceability to these measurements.
The ISO 10523 method¹⁰ was used to perform the pH measurements, including homogeneity and stability measurements. Calibration of pH meter and uncertainty estimation were performed using a bracketing procedure as recommended by the IUPAC^{19 (link)}. All measurements were carried out at (25 ± 1) °C. A pH meter (781 pH/Ion digital, Metrohm, Switzerland) with automatic temperature compensation (ATC), an automatic stirring system (801, Metrohm, Switzerland) and a glass electrode with a Pt-1000 temperature sensor (Unitrode, Metrohm, Switzerland) were used to measure pH. The certified buffer solutions mentioned above provided metrological traceability.

The ion content of young and old leaves, stems and roots was measured using Ion Chromatography (IC) system 850 Professional (Metrohm Switzerland). For this purpose, oven-dried tissues were ground to fine powder using a hammer mill with 1 mm sieve. Twenty-five mg per sample was ashed in a furnace at 550°C for 5 h. Ten ml of Milli-Q^® water was added to the ashes and these were shaken for 15 min at 5,000 rpm at 100°C. Prior to injection onto the IC system, samples were diluted 400 times with Milli-Q^®. Ion contents were calculated as the amount of ions per unit of dry weight (mg ion g^–1 dry mass) and the ion concentrations were estimated based on the water content of the tissue. The ratio K⁺/ Na⁺ was calculated based on mg K⁺/ mg Na⁺ content.