The single and combined effects of salinity and drought stresses on some agronomic traits, secondary metabolites and antioxidant activity of Ammi visnaga L.

The most important stresses in the world's agricultural lands, especially in Iran, are drought and salinity stresses, which are increasing in these days. In this study, the independent and combined effects of salinity and drought stresses were studied on different agronomic and biochemical traits of the medicinal plant of Ammi visnaga .The experimental design was performed as split plot based in a completely randomized block design with three replication. Drought stress treatments  based on soil depletion rate (normal 50%, moderate stress 60% and severe stress 85%) and  three salinity stress levels (normal, average stress: 80 mM and severe stress :100 mM were applied. The results of the present study showed that different levels of independent stresses and the combination of salinity and drought both caused a significant decrease in seed yield, seed weight and plant height and a significant increase in malondialdehyde content compared to the control treatment. In combined treatments, the changes in chlorophyll content did not show the same trend compared to the control treatment. In both drought and salinity stresses,there was a significant increase in the contents of total phenolics, total flavonols, total flavonoids, carotenoids, proline and antioxidant activity, compared to the control, in order to compensate  the negative effects of tensions. The lowest values for seed yield, plant height and the highest antioxidant activity were observed in the combined stress of severe drought and severe salinity.The highest content for total flavonols and carotenoid and the lowest value for malondialdehyde were observed in the combined stress of moderate drought and non salinity (D2S1). The highest contents of total phenolics (228.64 mg of gallic acid per gram of fresh leaves) and total flavonoids (120.62 mg of quercetin per gram of fresh leaves) were obtained in the combined stress of moderate salinity and severe drought (D3S2). The highest content of anthocyanin (0.12 μmol/g FW) in severe combined stress of salinity and drought (D3S3). These results showed the stimulating effects of these combined levels in the highest production of phenolics, flavonoids and anthocyanins compounds in this plant. Considering the significant increase of phenolic compounds in moderate and severe levels of drought and salinity stresses, its cultivation in lands affected by drought and salinity stress can be considered.