## 2 Materials and Methods  
### Experimental Design, Plant Material and Growth Conditions  
The trial was carried out in 2019 at the greenhouse facilities of the Department of Agriculture, Food, Environment and Forestry--University of Florence (Italy). A hydroponic system was set up, with 20 plastic containers (4 L volume) constantly aerated, under the same growing conditions as reported in [11]. The first trial took place from 26 March to 7 May testing _Tetragonia tetragonioides_ (Pallas) [PERSON]. at different salinity levels and conditions. _Tetragonia_ seeds were obtained by the Tuttosemi company (www.tuttosemi.com (accessed on 23 June 2021)) and germinated in a dark chamber at 18.5 \({}^{\circ}\)C starting from 8 January. About two months later, young plantlets were transplanted into 5 cm mesh pots filled with expanded clay and transferred in polystyrene layer (one plant per container) used as support in the hydroponic floating system. Half-strength Hoagland solution [27] was used as a growing medium for an additional 10 days, and plants were then gradually acclimated to the salinity conditions tested in the experiment. Salt acclimation occurred through the gradual (i.e., twice a week for a two-week period) addition of seawater or NaCl in the respective treatments, until the achievement of the final concentrations. Five treatments were set up: C (control, half-strength Hoagland solution, EC = 1.5 dS m\({}^{-1}\)); M-SW (moderate seawater, 25% seawater and 75% half-strength Hoagland solution, EC = 14.5 dS m\({}^{-1}\)); M-SA (moderate salt, 150 mM NaCl half-strength Hoagland solution, EC = 13.5 dS m\({}^{-1}\)); H-SW (high seawater, 50% seawater and 50% half-strength Hoagland solution, EC = 24.5 dS m\({}^{-1}\)); H-SA (high salt, 280 mM NaCl half-strength Hoagland solution, EC = 23.5 dS m\({}^{-1}\)), for a total of four plants per treatment, randomly distributed. The second trial was carried out from 20 May to 20 June with _Lactuca sativa_ L. Plantlets obtained from a nursery were transplanted into 5 cm mesh pots filled with expanded clay. They were adapted to hydroponic conditions and then gradually acclimated to salinity conditions, up to the beginning of the trial. As for _Tetragonia_, salt acclimation occurred through the gradual addition of seawater or NaCl reaching in 10 days the final concentrations. Afterwards, plants were grown under the following salinity conditions: C (control, half-strength Hoagland solution, EC = 1.5 dS m\({}^{-1}\)); M-SW (moderate seawater, 5% seawater and 95% half-strength Hoagland solution, EC = 4.5 dS m\({}^{-1}\)); M-SA (moderate salt, 50 mM NaCl half-strength Hoagland solution, EC = 5.5 dS m\({}^{-1}\)); H-SW (high seawater, 15% seawater and 85% half-strength Hoagland solution, EC = 12.5 dS m\({}^{-1}\)); H-SA (high salt, 100 mM NaCl half-strength Hoagland solution, EC = 12.5 dS m\({}^{-1}\)), again for a total of four plants per treatment, randomly distributed. For both experiments, samples from the nutrient solution were collected twice a week to measure pH and EC by a laboratory pH meter (pHmeter PHM 210 Meter Lab, Radiometer Analytical, Lyon, France) and the nutrient solutions (treatments) were replaced every two weeks. Seawater used in the experiment was collected at Marina di Pisa (Italy) one week before the beginning of each experiment and stored in 20 L sterile tanks at 4 \({}^{\circ}\)C. The chemical and physical characteristics of seawater are reported in Table 1.  
Throughout both trials, plants were maintained at relative humidity ranging from 40% to 55%, natural light, (light intensity reaching 700 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\) during sunny days) and 28 \({}^{\circ}\)C/18 \({}^{\circ}\)C day/night air temperature.