| چکیده انگلیسی مقاله |
Background and objectives: Among the 16 species of Satureja in Iran, 10 are endemic, including S. bachtiarica, S. khuzistanica, S. intermedia, S. sahendica, S. isophylla, S. rechingeri, S. edmondi, S. kallarica, S. atropatana, and S. kermanshahensis. Satureja sahendica Bornm. is a perennial plant with essential oil widely used in the pharmaceutical, food, health, and cosmetic industries. Its antiviral properties have also been documented. Drought stress is one of the most significant environmental challenges for plants, leading to reduced water absorption, stomatal conductance, transpiration, and photosynthesis, while also disrupting hormonal balance. Plants adopt various mechanisms to mitigate drought stress, such as increasing osmotic regulators like sugars, proline amino acids, and proteins. Drought conditions typically decrease chlorophyll content while increasing carotenoids. Additionally, oxidative stress intensifies under drought, leading to the accumulation of reactive oxygen species such as catalase, superoxide dismutase, and ascorbate peroxidase in chloroplasts and mitochondria. Mycorrhizal fungi play a crucial role in enhancing root absorption, regulating water movement within host plants, and ultimately improving tissue water uptake and leaf physiology.
Methodology: This experiment was conducted using a split-plot design within a randomized complete block design (RCBD) with three replications at the Research Institute of Forests and Rangelands during 2015–2016. The main factor was irrigation treatment, consisting of full irrigation (control), irrigation interruption at the stem stage (resumed at the budding stage), irrigation interruption at the budding stage (no irrigation until the end of the flowering period), and irrigation interruption at the 50% flowering stage (no irrigation until the end of flowering). The secondary factor was biological fertilizer application, which included no biofertilizer (control), inoculation with Glomus intraradices, inoculation with Glomus mosseae, and inoculation with Glomus mosseae + Glomus intraradices. Throughout the growth period, irrigation was maintained at 80–90% of field capacity, and drought treatments were applied based on plant morphology. The biofertilizers contained mycorrhizal fungi (Glomus intraradices and Glomus mosseae) in the form of active fungal structures, including spores, hyphae, and roots. Before transplanting the seedlings, 10 grams of biofertilizer, containing 400 to 500 active fungal units, was applied to each planting hole.
Results: The interaction effect of drought stress and mycorrhiza was significant at the 1% probability level for protein, catalase, superoxide dismutase, peroxidase, chlorophyll a, total chlorophyll, proline, polyphenol oxidase, soluble sugars, essential oil percentage, essential oil yield, and flowering shoot yield, while its effect on carotenoid and total phenol was significant at the 5% level. The results indicated that the yield of p-cymene, γ-terpinene, and thymol was significantly influenced at the 1% level by the triple interaction of year, drought stress, and mycorrhiza. Mean comparisons revealed that catalase, superoxide dismutase, chlorophyll b, proline, total phenol, essential oil percentage, and essential oil yield were higher in the second year. Regarding drought stress, the highest flowering shoot yield was observed under full irrigation and moisture stress applied at the full flowering stage. Mycorrhizal treatment comparisons showed that the highest malondialdehyde release occurred in plants without inoculation and those treated with the combination of Glomus intraradices + Glomus mosseae. Essential oil analysis revealed that the highest percentage (2.23%) was obtained in the budding stage treatment with G. mosseae, while the highest essential oil yield (51.78 kg/ha) was recorded under full irrigation with G. intraradices inoculation. The triple interaction (year × drought stress × mycorrhiza) analysis showed that in the first year, the highest thymol yield (74.59%) resulted from full irrigation combined with G. mosseae inoculation.
Conclusion: Therefore, it can be concluded that the application of biological fertilizers effectively mitigated the effects of drought stress, leading to an increase in both the essential oil percentage and thymol content. |