## 2 Materials and Methods
### Plant Materials, Growth Conditions, and Experimental Setup  
Three commercial greenhouse tomato (_Solanum locyopersium_ L.) cultivars, Ghandowra-F1 ([PERSON], Enkhuizen, The Netherlands), Valouro-RZ ([PERSON], De Lier, The Netherlands), and Feisty-Red (Seminis, St. Louis, MO, USA) were used as scions. The selected scion cultivars were grafted onto a commercial rootstock, Maxifort (_S. lycopersium_\(\times\)_S. hhrochaites_, De Ruiter Seeds/Monsanto, Bergschenhoek, The Netherlands). Non-grafted plants of the three tomato cultivars were used as the control. Tomato rootstocks and scion seedlings with identical stem diameters at similar growth stages were selected for grafting. To ensure similar stem diameter and differences in growth vigor, the rootstock seeds were sown five days earlier than the seeds of the scions [34; 35; 36]. A tube grafting technique was adopted, and the grafted seedlings were kept at controlled conditions at a temperature between 22 \({}^{\circ}\)C and 24 \({}^{\circ}\)C and a relative humidity of 85-90%, with 45% shade, for seven days for their better survival [37]. Healthy seedlings of grafted and non-grafted tomatoes were transplanted into a hydroponic glass greenhouse at the four-leaf stage on 6 February 2020 (1 st season) and 25 November 2020 (2 nd season). The experiments were conducted in both seasons using a split-split-plot system and a randomized complete block design with three replicates. Three salinity levels designed as low (\(\sim\)2.5 dS m\({}^{-1}\)), moderate (\(\sim\)6.0 dS m\({}^{-1}\)), and high (\(\sim\)9.0 dS m\({}^{-1}\)) and four nutrient recipes (N1-N4) were used in both the first and second seasons (Table 1). The control nutrient solution (N1) was prepared with water-soluble fertilizers, as recommended by [PERSON] and [PERSON] [38]. The rest of the nutrient recipes (N2-N4), as presented in Table 2, were prepared by adding more concentrations of K and Ca to the control recipe (N1), where N2 was N1 + 15% additional amount of K, N3 was N1 + 15% additional amount of Ca, N4 was N1 + 15% additional amount of both K and Ca. The EC of the fertilizer solution was maintained at ~2.0 dS.m\({}^{-1}\) for each salinity level. In the case of salinity level S1, municipality-supplied water with an EC of ~1.0 dS.m\({}^{-1}\) was used and the N1 solution was prepared with an EC of ~3.0 dS.m\({}^{-1}\). In the case of the S2 and S3 treatments, an EC of 2 dS.m\({}^{-1}\) was maintained for the fertilizer recipe, and the EC of the solutions was adjusted with added NaCl dissolved in municipality-supplied water to a final value of ~6.0 and ~9.0 dS.m\({}^{-1}\), respectively. To prevent possible osmotic shock, NaCl concentration was initiated at 20 mM and then gradually increased until reaching the targeted concentration, as described in [39]. The pH and EC of the nutrient solutions were monitored frequently using hand-held pH and EC devices. A programmed irrigation schedule was prepared to supply the nutrient solutions to the plants. The schedule was set based on the incoming solar radiation, plant transpiration demands, and growth stage. The \"irrigation start mode\" was set at an accumulated radiation threshold of 400 flux, and the \"irrigation stop mode\" was set based on attaining the selected dose [40]. The nutrient concentration of each solution was tested for EC and pH on a daily basis. The pH range was set from 5.5 to 6.5, and the targeted EC and pH values were adjusted by adding acidic and sodic solutions, without affecting the target