S06 - Session P4 - The effects of root zone cooling on lettuce physiology under heat stress

Authors: Hyungmin Rho *, Jing-Yuan Hung

Root zone cooling is a widely-used technology in greenhouse production as a relatively more accessible and cheaper way to increase the yield of crops. Lettuce ( Lactuca sativa L.) is one of the most important vegetables in the world. There is a large amount of lettuce grown in greenhouses. Lettuce was grown at 35/30°C (H-T air ) and 30/25°C (L-T air ) day/night air temperature with and without cooling solutions in deep flow technology hydroponic system. The shoot fresh weight significantly increased in cooling groups compared to control groups in both air temperatures, while the root fresh weight significantly decreased in cooling groups. The shoot water content of cooling groups decreased by 4% at H-T air but it showed no difference at L-T air . The root water content increased by 6% and 10% at L-T air and H-T air , respectively. Root zone cooling decreased the plants' water-use efficiency (WUE) by 50% at L-T air . However, it increased the WUE by 80% at H-T air . Leaf temperature (T leaf ) significantly decreased with no difference found on stomatal conductance (g sw ) and transpiration rate (E) at L-T air . On the other hand, T leaf differentiation showed no consistent patterns during the one month of growing. The plant morphology effects of root zone cooling showed different trends at H-T air and L-T air . T leaf cooling under L-T air was not the result of the increased g sw or E. The reason for T leaf cooling needs to be further investigated.