| چکیده انگلیسی مقاله |
Background and objectives: Garden thyme (Thymus vulgaris L.) is prominent among medicinal plants due to its applications across various industries. Salinity is the second most significant environmental factor limiting agricultural productivity in many regions worldwide, including Iran. Biofertilizers, which supply macro- and micronutrients, amino acids, and plant hormones, can enhance plant growth and improve stress resistance. This study examined the effects of thyme extract (Thymbra spicata), seaweed, and a comprehensive bacterial biofertilizer on garden thyme's morphophysiological traits, biochemical characteristics, essential oil yield, and secondary metabolite production under salt stress conditions.
Methodology: This research was designed and implemented as a factorial experiment based on a randomized complete block design with three replications, conducted in the medicinal plant research greenhouse of Ilam University. The first factor included treatments of 10% T. spicata extract (TS), 1% seaweed (SB), 10% complete bacterial biofertilizer (BB), and their combination (TS+SB+BB). The second factor involved three salinity levels: 0, 100, and 200 mM sodium chloride (S0, S100, and S200). In this study, in addition to morphological traits, the following parameters were measured: relative water content, electrolyte leakage, total chlorophyll, carotenoid and anthocyanin contents of shoots, total phenol, flavonoid, total protein, soluble sugar, proline, malondialdehyde, the enzyme activities of catalase and phenylalanine ammonia-lyase, antioxidant activity, and essential oil content. Essential oil components were also identified using GC and GC/MS. After data collection, the results were analyzed statistically using SAS 9.3 software, and Duncan’s multiple range test was used to compare means at a 5% probability level. The findings were presented in tables and graphs using Excel.
Results: Based on the results, increasing salinity stress led to a decline in the average values of morphological, physiological, and biochemical indices of T. vulgaris. However, the application of biofertilizer treatments mitigated the adverse effects of salinity. According to the mean comparisons, under both non-stress and salinity stress conditions, the highest morphological indices were observed in the combined treatment of TS+SB+BB. This combined treatment also enhanced relative water content, chlorophyll, carotenoid, anthocyanin, total phenol, flavonoid, total protein, soluble sugar, and proline at all stress levels. In terms of carotenoid, anthocyanin, total phenol, flavonoid, proline, soluble sugar, catalase, and phenylalanine ammonia-lyase enzyme activities, and antioxidant properties, values generally increased with higher stress levels. The highest phenylalanine ammonia-lyase activity and antioxidant activity were recorded under both non-stress and moderate stress conditions with the TS treatment, while under high-stress conditions, the TS+SB+BB combination showed the greatest activity. Salinity stress also increased electrolyte leakage and malondialdehyde (MDA) content. However, at all three salinity levels, the application of the TS+SB+BB treatment significantly reduced electrolyte leakage and MDA content. In this study, the highest essential oil content was observed under moderate salinity stress (S100) in plants treated with the TS+SB+BB combination, which also increased thymol content by 45% compared to the control.
Conclusion: The results of the morphophysiological and biochemical assessments, along with essential oil analysis of garden thyme, revealed a significant decline in photosynthetic activity under salt stress conditions. This reduction was accompanied by decreased leaf water status and a decline in various growth and biochemical parameters. The interaction between salinity stress and the TS+SB+BB biofertilizer treatment demonstrated that plants receiving the combined treatment experienced less reduction in growth, physiological, biochemical, and essential oil parameters under high salinity stress compared to untreated controls. Overall, it can be concluded that the combined biofertilizer treatment effectively mitigates the negative effects of salinity stress, supporting improved quantitative and qualitative performance of garden thyme under adverse conditions. |