Ameliorative effects of foliar potassium nitrate on the growth, physiological, and stomatal properties of lettuce plants under salinity stress

The restorative effects of foliar potassium nitrate spraying on morphological, physiological, and stomata properties of salt-affected lettuce (Lactuca sativa L.) cv. Yedikule plants were investigated. Lettuce seedlings grown under saline irrigation water constituted by NaCl levels with 50, 100, 150, and 200 mM were sprayed with foliar KNO3 at 500 mg L-1 after 30-day-old plants. Salinity stress adversely influenced plant growth and physiological parameters. Fresh plant biomass, leaf area per plant, and leaf number were limited at 100 mM NaCl and above. Leaf temperature, chlorophyll content, dry matter, turgor loss, and electrolyte leakage were enhanced under saline conditions; however, salinity diminished leaf relative water content. Foliar KNO3 spraying improved the physiologic and stomata traits of salt-affected lettuce plants rather than plant growth. The electrolyte leakage was increased by increasing salinity and KNO3 spraying, whereas the relative injury was lower in the plants treated with foliar KNO3. An increase in stomata density was detected up to 100 mM NaCl, while stomata length and width were gradually decreased. Salinity and foliar KNO3 resulted in more frequent stomata number up to 100 mM NaCl, but it was surprisingly reduced at higher NaCl levels. Lettuce plants could grow up with irrigation water salinity of 100 mM and foliar KNO3 with 500 mg L-1 could regulate the adverse effects of salinity on the physiological characteristics up to 100 mM NaCl.