Effects of zinc nanoparticles on growth, some physiological characteristics, and essential oil yield of Dracocephalum moldavica L. under salinity stress conditions

Soil salinity in arid and semi-arid regions is one of the most important abiotic stresses causing negative effects on the growth and yield of medicinal plants. To investigate the effect of Zn nanoparticles foliar spray at different levels on growth characteristic, antioxidant enzymes, and essential oil yield of dragonhead (Dracocephalum moldavica L.) under salinity stress conditions, a factorial experiment was conducted in a completely randomized design with three replications in the greenhouse of Mohaghegh Ardabili University during 2018-2019. Experimental treatments included salinity stress at four levels (0, 50, 100, and 150 mM of NaCl) and foliar spray with Zn nanoparticles at three levels (0, 100, and 500 mg.l-1). Traits including plant height, aerial parts fresh and dry weight, chlorophyll, cell membrane electrolyte leakage, relative water content, proline, antioxidant enzymes, and percentage and yield of essential oil were measured. Results showed that salinity significantly decreased plant height, shoot fresh and dry weight, chlorophyll, the relative water content of leaves, and essential oil yield, and increased electrolyte leakage from cell membranes and proline content of the leaves. While nano-Zn foliar spray reduced the negative effects of salinity stress by increasing the growth and activity of antioxidant enzymes such as ascorbate peroxidase and superoxide dismutase. Treatment of 500 mg.l-1 nano-Zn caused the best-improving effect on traits including plant height, stem dry weight, chlorophyll, electrolyte leakage, antioxidant enzymes, and essential oil yield under salinity stress conditions. Therefore, the use of 500 mg.l-1 nano-Zn is recommended as a reduction of the negative effects of salinity stress in dragonhead.