OPTIMIZING LETTUCE PRODUCTION THROUGH GEOTHERMALHEATING: IMPACTS ON MORPHOLOGY AND BIOACTIVE COMPOUNDACCUMULATION
Lettuce (Lactuca sativa L.) is a highly valued and nutritionally important crop. The goal of new production technologies is to shorten the vegetation period, allowing for a higher number of harvests, while preserving the environment and improving the nutritional quality of lettuce. This study investigated the effect of geothermal heating on growth dynamics and the accumulation of bioactive compounds in lettuce. Two production systems were compared: a greenhouse with geothermal heating and one without heating. The geothermal system provided a more stable soil temperature, which significantly shortened the vegetation period by 31 days. In contrast, lower soil temperatures in the unheated greenhouse enhanced secondary metabolism, leading to higher concentrations of phenolic compounds (80.5 mg GAE/100 g), flavonoids (2.37 mg/100 g), and increased antioxidant capacity (112.7 μmol Fe²⁺/100 g). These results indicate that temperature regimes strongly influence both primary growth processes and the synthesis of bioactive compounds in lettuce. Geothermal heating ensures faster crop development but may reduce the accumulation of certain antioxidants. Future research should aim to optimize temperature management to balance yield, energy efficiency, and nutritional quality in greenhouses lettuce production.