**2. Materials and Methods**

#### *2.1. Characteristics of Lettuce Varieties*

For our experiments, two varieties of lettuce were chosen—a semi-head green-leaved variety called 'Azart' and a red-leaved variety called 'Lollo Rossa'. These varieties belong to different groups in terms of colour and structure, in addition, they are grown well in hydroponic culture and have been tested by us in previous experiments [20]. The 'Azart' lettuce variety ("Prestige" company)—mid-season semi-head lettuce. The rosette of leaves is semi-erect, 25–27 cm high, and 31–32 cm in diameter. The texture of the leaf tissue is tender and semi-crispy. The mass of a head of cabbage reaches 230 g 'Lollo Rossa' lettuce variety is a mid-season variety of leaf lettuce. The rosette of leaves is semi-erect, 20 cm high, 30 cm in diameter, weighing 200–350 g. Productivity is 3 kg/m2.
