The temperature of the nutrient solution in hydroponic crops of lettuce is a determinant of biomass yield and affects several physiological mechanisms of the plant. The aim of this study is to evaluate the influence of nutrient solution temperature on the levels of nitrate and pigments in leaves, as well as green mass yield and thermal flow in lettuce crop hydroponically. The experiment was conducted in a greenhouse at the Federal Technological University of Paraná. The nutrient solution was maintained at three temperatures (15 and 25°C and environmental temperature). The accumulated nitrate in leaf and photosynthetic pigment level were evaluated five times (28, 35, 42, 49 and 56 days after sowing). The total green mass yield and thermal flow behavior in the plants were assessed through thermographic analysis. The temperature of the solution influenced the levels of nitrate, chlorophyll and carotenoids in lettuce leaves, and green mass, which were larger at 25°C treatment. The root and stem had thermal equilibrium with the nutrient solution, while the temperature at the middle and upper part of the plant is similar to that of the environment.
Key words: Lactuca sativa, pigments, nitrate, heat conduction, green mass.
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