Interactive Effects of Different Foliar Potassium Sources on Growth, Physiology, and Phytochemical Quality of Eruca sativa L. Plants Grown Under Saline Conditions

Abstract

Due to the lack of irrigation water in hot, arid regions, saline water has been suggested to largely meet the water needs of crops, especially leafy vegetables. Rocket (Eruca sativa L.) plants were grown in hydroponics under two salinity treatments (0 and 75 mM NaCl) supplemented with the nutrient solution. The alleviation of salinity-induced stress with different potassium (K) sources (KNO3, K2SO4, KH2PO4, and KOH) via foliar application was examined through plant physiological and biochemical characteristics. Control plants were water-sprayed (WS). The findings showed that salt stress had a negative impact on stomatal limitation, whereas it increased the number of leaves and leaf transpiration rates, sodium accumulation in leaves, total phenols, and oxidative stress through lipid peroxidation (malondialdehyde—MDA—content). However, the foliar application of K increased fresh and dry biomass (except for KOH) and maintained marketability of leaves (only when plants were treated with KNO3), regardless of the salinity treatment. Potassium sources had little or no effects on photosynthetic rates, plant physiological parameters, total phenols and oxidative stress, whereas they stimulated K uptake and enhanced the K:Na ratio in leaves. Moreover, the application of K2SO4 under saline conditions decreased plant height, leaf number, chlorophyll fluorescence, and leaf stomatal conductance, whereas it stimulated water use efficiency and K content in leaves. According to the current findings, rocket can be regarded as a moderately salt-tolerant species that can thrive at the salinity levels tested in this study (e.g., 75 mM NaCl). Therefore, the supplementation of various K sources via foliar sprays, primarily in the form of KNO3 and K2SO4, has been shown to be an effective means to mitigate the stress impacts associated with elevated salinity.