Effects of Nutrient Solution Heating on the Root Development and Yield of Three Lettuce Cultivars (Lactuca sativa L.) Grown in NFT and Aeroponic Systems under Low-Temperature Conditions

This study investigated the effects of nutrient solution heating (NSH) on the root-zone temperature (RZT), root development, shoot growth, and yield of three lettuce cultivars (Lactuca sativa L.) grown in two water culture systems, the Nutrient Film Technique (NFT) system and an aeroponic system, during a low-temperature period.Three cultivars ('Caipira', 'Volare', and 'Isabel') were cultivated in a glasshouse using nutrient solutions heated to set temperatures of 20, 25, and 30°C.NSH effectively increased the RZT in both the NFT and aeroponic systems.However, the aeroponic system exhibited noticeably greater temperature stability than the NFT system owing to its Styrofoam-insulated and enclosed structure.Heated nutrient solutions significantly promoted root development by, for instance, increasing the overall root length, number of tips, and the lateral roots while decreasing the average root diameter, indicating enhanced root formation, which is beneficial for water and nutrient uptake and transport.Growth and harvest characteristics, specifically the leaf length, no. of leaves, chlorophyll contents, leaf area, shoot fresh/dry weight, and root fresh/dry weight, also improved with higher RZTs.The NFT system showed higher shoot biomass and yield outcomes, whereas the aeroponic system exhibited superior root development and greater root biomass.Among the tested temperatures, NSH30 resulted in better growth and yield levels than NSH20 and NSH25.Although the nutrient solution was heated to 30°C, the actual RZT achieved was approximately 25°C, which was found to be optimal for lettuce root and shoot growth.These findings suggest that nutrient solution heating is an effective strategy to enhance lettuce productivity in NFT and aeroponic systems during low-temperature periods.