Growth and photosynthesis of salt-stressed sunflower (Helianthus annuus) plants as affected by foliar-applied different potassium salts

In order to assess the effectiveness of foliar-applied potassium (K+, 1.25%) using different salts (KCl, KOH, K2CO3, KNO3, KH2PO4, and K2SO4) in ameliorating the inhibitory effect of salt stress on sunflower plants, a greenhouse experiment was conducted. Sodium chloride (150 mM) was applied through the rooting medium to 18 cl-old plants and after 1 week of salt treatment; different K+-containing salts were applied twice in 1-week interval as a foliar spray. Salt stress adversely affected the growth, yield components, gas exchange, and water relations, and also caused nutrient imbalance in sunflower plants. However, foliar-applied different sources of potassium improved shoot and root fresh and shoot dry weights, achene yield, 100-achene weight, photosynthetic rate, transpiration rate, stomatal conductance, water-use efficiency, relative water content, and leaf and root K+ concentrations of sunflower plants grown under saline conditions. Under nonsaline conditions, improvement in shoot fresh weight, achene yield, 100-achene weight, photosynthetic and transpiration rates, and root Na+ concentration was observed due to foliar-applied different K sources. Of the different salts, K2SO4, KH2PO4, KNO3, and K2CO3 were more effective than KCl and KOH in improving growth and some key physiological processes of sunflower plants.