Humic acid affects some growth parameters, chlorophyll, flavonoids, antioxidant enzymes and essential oil of Satureja khuzestanica Jamzad under salinity stress

Salinity stress is a limiting factor for plant growth and production. To reduce the salinity effects, humic acid was applied in soil, and its mitigation effect was studied on Satureja khuzistanica Jamzad. The research was conducted as a factorial experiment based on a completely randomized block design with four replications at Lorestan University. The factors included salinity stress (0, 25, 50, 75, and 100 mM NaCl) and humic acid (0, 10, 20, 30, and 40 mg/kg soil). Results showed that salinity stress decreased plant height, dry weight, leaf number, root length, chlorophyll, and carotenoids. However, it significantly increased flavonoid contents and SOD, CAT, and GR activities. Essential oil (EO) quantity and quality were affected by salinity. The EO percentage and yield decreased by salinity. Forty-three constituents were identified, among which carvacrol, γ-terpinene, α-terpinene, myrcene, p-cymene, α-thujene, citronellol, and α-pinene were the major compounds according to their contents and formed more than 94% of the EO. The percentage of some of the other constituents decreased to zero under specific salinity and humic acid treatments. The application of humic acid could mitigate salinity effects on growth and EO production. However, there was an interaction between salinity and humic acid on EO yield and quality. It seems that the application of humic acid is useful for improvement EO yield of S. khuzestani, but the amount of its application depends on the EO consumers’ favorite.