The impact of foliar fertilizers on growth, and biochemical responses of Thymus vulgaris to salinity stress

Authors: ZRIG, AHLEM - Faculty Of Sciences Of Gabes; Ferreira, Jorge; HAMOUDA, FOUED - University Of Gabes; TOUNEKTI, TAIEB - Jazan University; SELIM, SAMY - Jouf University; JAOUNI, SOAD - King Abdulaziz University; KHEMIRA, HABIB - Faculty Of Sciences Of Gabes; ABDELGAWAD, HAMADA - University Of Antwerp

Submitted to: Arid Land Research and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2018
Publication Date: 1/12/2019
Citation: Zrig, A., Ferreira, J.F., Hamouda, F., Tounekti, T., Selim, S., Jaouni, S.A., Khemira, H., Abdelgawad, H. 2019. The impact of foliar fertilizers on growth, and biochemical responses of Thymus vulgaris to salinity stress. Arid Land Research and Management. 33(3):297-320. https://doi.org/10.1080/15324982.2018.1551817.
DOI: https://doi.org/10.1080/15324982.2018.1551817

Interpretive Summary: Salinity stress reduces plant growth, biomass, yield, and may lead to death when severe. Different species have diverse responses to salinity stress. These responses may be biochemical, physiological, or expressed through a mineral imbalance in the plant. In this work, we hypothesized that, spraying salt-stressed thyme leaves with solutions containing potassium or calcium could mitigate the negative effects of salinity on plant growth and metabolism. To test this hypothesis, thyme plants were cultivated under salt stress, with irrigation water containing 100 mM NaCl (approximately 1/5 of seawater salinity) for two and four weeks before applying foliar sprays of potassium or calcium. Also, to test the effect of stress relief, treated plants were allowed two weeks of recovery after four weeks of salt stress. In general, after salinity stress, thyme plants had their leaf fresh weight reduced by 31% (after two weeks) and 43% (after four weeks). Salinity decreased the relative water content, water and osmotic potentials and led to ion imbalances and nutrient deficiencies. Salinity also altered some essential oil components, but leaf antioxidants remained fairly stable, except for a significant increase for plants under salt stress, and sprayed with potassium two weeks after treatment. Results indicated that stressed plants accumulated significantly more soluble sugars and amino acids. Foliar sprays with potassium and calcium reversed some of the negative effects of salinity on plant biomass and induced the accumulations of some compatible solutes, such as glucose, sucrose, fructose, and starch four weeks after salinity stress. Moreover, some essential oil components and gallic acid increased in sprayed plants, but these effects were dependent on the type and duration of the treatment. Overall, the effects of salinity stress and/or potassium and calcium treatments were also observed after the two-week recovery period. Overall, spraying leaves with potassium and calcium appeared to mitigate some of the stresses caused by salinity in Thymus vulgaris.

Technical Abstract: Salinity reduces plant biomass and may lead to death when severe. To cope with the negative effects of this stress, plant species present specific physiological or biochemical responses. In this work, we hypothesized that spraying salt-stressed thyme leaves with K+ and Ca2+ could mitigate the negative effects of salinity on plant growth and metabolism. To test this hypothesis, we grew thyme plants under salinity stress for two and four weeks before applying foliar sprays. Also, to test the effect of stress relief, treated plants were allowed two weeks of recovery after four weeks of salt stress. In general, after two and four weeks of salinity stress, the leaf fresh weight of thyme plants was reduced by 31 and 43%, respectively. Salinity also decreased the relative water content, water, and osmotic potentials and led to ion imbalances and nutrient deficiencies. Salinity altered concentration of some essential oils, but leaf antioxidant contents remained fairly stable, except for a significant increase for plants under NaCl+KCl two weeks after treatment. Our results indicated that stressed plants accumulated significantly more soluble sugars and amino acids in comparison with the control. Foliar sprays with KCl and CaCl2 reversed the negative effects of salinity on plant biomass and induced the accumulations of compatible solutes. Moreover, concentrations of some essential oils and gallic acid increased in sprayed plants, but these effects were dependent on the type and duration of the treatment. Overall, spraying leaves with K+ and Ca2+ was able to mitigate salinity stress in Thymus vulgaris even during the recovery period.