<![CDATA[This study investigates the effects of root-zone cooling (RZC) on the growth performance of Grand Rapids lettuce (Lactuca sativa L.) cultivated in a deep water culture hydroponic (DWC) system. The experiment evaluated three cooling treatments 15 °C, 20 °C, and 25 °C applied for 8 hours daily, with an untreated control group for comparison. Morphological parameters including plant height, leaf area, SPAD value, root length, and fresh weight were measured over a 30-day growth period. Results demonstrated that RZC significantly improved all growth metrics compared to the control. The 25 °C treatment consistently outperformed other groups, yielding the tallest plants (32 cm), largest leaf area (200 cm²), and highest fresh weight (97.5 g), indicating enhanced nutrient uptake and photosynthetic activity. Root length was also maximized at 20 °C and 25 °C, reflecting improved root system development under moderate cooling. While chlorophyll content (SPAD value) showed less variation among treatments, temperatures below 20 °C appeared to limit metabolic efficiency. These findings confirm that RZC, particularly at 25 °C, enhances morphological development and biomass accumulation in hydroponic lettuce, offering a promising strategy for optimizing growth under warm environmental conditions. The study underscores the importance of precise root-zone temperature control as a sustainable intervention to mitigate heat stress, improve resource use efficiency, and boost productivity in soilless cultivation systems.]]>
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