Effect of humic acid and ascorbate on growth and biochemical traits of Moldavian balm (Dracocephalum moldavica L.) under salinity stress

Salinity is one of the most important non- biological stresses which limit the production of agricultural yields in dry and semi arid regions. Humic acid as an organic acid and ascorbate as a powerful antioxidant can improve yield of plants under salt stress. In order to investigation effects of salinity and its interaction with ascorbate and humic acid on growth, photosynthetic pigments content, antioxidant enzymes activity and soluble protein in Moldavian balm (Dracocephalum moldavica L.), a factorial experiment was conducted based on randomized complete design with three replications. Treatments included four levels of salinity (0, 50, 100 and 150 mM), three levels of ascorbate and humic acid (0, 100 and 200 mgL-1). Vegetative traits such as plant height and fresh and dry weight of stems and leaves with increasing salinity concentration showed a significant decrease compared to control. Humic acid application especially 200 mg.L-1 was improved traits than the control plants in high levels of salinity stress. Photosynthetic pigments were strongly decreased by salinity and application of 200 mgL-1 humic acid and ascorbic acid (partly) could compensate effects of salinity. The highest activity of antioxidant enzymes was observed in 50 mM salinity stress. Application of humic acid (especially 200 mgL-1) for catalase and ascorbate peroxidase and 200 mgL-1 ascorbic acid for guaiacol peroxidase increased enzymes activity compared to the control treatment.