Morphophysiological characteristics, quantity and quality of lemon balm (Melissa officinalis L.) essential oil under the influence of silicic acid in soilless cultivation

Many studies have been conducted on the role of essential elements in various aspects of medicinal plant production. However, the role of silicon (Si) as a quasi-essential or beneficial element in the growth and development, quantity and quality of essential oil of many medicinal plants is unknown. In this regard, different concentrations of silicic acid including 0 (control), 25, 50, 75, 100, and 125 mg l-1 were added to the standard Hoagland and Arnone nutrient solution, and morphophysiological reactions and secondary metabolites production of lemon balm (Melissa officinalis L.) were evaluated in soilless cultivation (hydroponic system). The fresh and dry weight of leaves and roots increased with the addition of Si to the nutrient solution compared to the control. The percentage of biomass changes varied depending on the concentration of Si, so that the plant fresh weight at 125 mg l-1 of Si increased by 41% compared to the control (without Si). However, the percentage of essential oil (fresh materials) in plants fed with Si increased significantly compared to control. Accordingly, the percentage of essential oil in different Si concentrations including 0, 25, 50, 75, 100 and 125 mg l-1 were 0.16, 0.21, 0.31, 0.33, 0.34 and 0.34(%), respectively. The reaction of lemon balm essential oil compounds to Si also indicated the important role of this element in the quality of the essential oil produced. The highest amounts of geraniol (21.27%) and citral (58.71%) were obtained in concentrations of 50 and 125 mg l-1 of Si, respectively. Also, the most important main compounds in various concentrations of Si (mg l-1) included citral+geraniol (Conc.0), citral+neryl (Conc.25), citral+linalool (Conc.50), citral+caryophyllene oxide (Conc.75), citral+geranyl acetate (Conc.100) and citral+geranyl (Conc.125). Based on the results of the experiment, Si as a beneficial element has a significant effect on the growth and development parameters, yield, and quality of essential oil of lemon balm.