Dry-fog Aeroponics Affects the Root Growth of Leaf Lettuce (Lactuca sativa L. cv. Greenspan) by Changing the Flow Rate of Spray Fertigation

Abstract

The growth characteristics and physiological activities of leaves and roots of lettuce cultivated in dry-fog aeroponics with different flow rates of nutrient dry-fog (FL, 1.0 m s (cid:4) 1 ; NF, 0.1 m s (cid:4) 1 ) were investigated under a controlled environment for two weeks and compared to lettuce cultivated using deep-flow technique (DFT). The growth of leaves of FL and DFT was not different and was significantly higher than that of NF. The amount of dry-fog particles adhering to the objects was higher in FL than in NF, so that the root growth in NF was significantly higher than that of FL. The respiration rate of roots was significantly higher in dry-fog aeroponics, but the dehydrogenase activity in the roots was significantly higher in DFT. There were no differences in the contents of chlorophyll and total soluble protein in the leaves or the specific leaf area. Photosynthetic rate and stomatal conductance were higher in dry-fog aeroponics. The contents of nitrate nitrogen, phosphate and potassium ions in the leaves were significantly higher in DFT, but the content of calcium ions was significantly higher in FL. Thus, changing the flow rate of the dry-fog in the rhizosphere can affect the growth and physiological activities of leaves and roots.