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Background Zataria multiflora Boiss. is a medicinal and aromatic plant from the Lamiaceae family. It is extensively used in Iranian traditional medicine, mostly as a replacement for Thyme species. This study was focused on the analysis of chemical composition and the distribution and types of trichomes of Z. multiflora grown under different conditions. Equilibrium headspace analysis in combination with GC-FID-MS was used to identify volatile compounds released by aerial parts of Z. multiflora in development stages of 50 and 100% flowering under normal and drought-stress conditions. Results The main constituents were p-cymene (20.06–27.40%), γ-terpinene (12.44–16.93%), and α-pinene (6.91–16.58%) and thymol (8.52–9.99%). The highest content of p-cymene (27.40%) and thymol (9.99%) was observed in the 50% flowering stage at the 90% field capacity, while the maximum γ-terpinene (16.93%) content was recorded in the 100% flowering stage under normal conditions. Using the SEM method, it was found that peltate glandular and non-glandular trichomes are distributed on the surface of the leaf, stem, and outer side of the calyx. However, capitate trichomes only are detected on the stem and calyx in the 100% flowering and beginning of blooming stages, respectively. The type and structure of trichomes do not vary in different development stages, but they differ in density. The highest number of leaf peltate glandular trichomes was observed in the vegetative and beginning of blooming stages at 50% and 90% field capacity, respectively. Non-glandular trichomes of the stem were observed with high density in both normal and stress conditions, which are more densely in 90% field capacity. Conclusions Since this plant has strong potential to be used in the food and pharmacological industries, this study provides valuable information for its cultivation and harvesting at specific phenological stages, depending on desired compounds and their concentrations.

Owing to the overuse of wild land, the mountainous watersheds in Iran have experienced severe land degradation and consequent downstream flooding. To design effective soil and water conservation strategies, it is crucial to understand how sediment yield and flow fluctuations respond to conservation practices. The purpose of this study was to evaluate the GeoWEPP model for runoff and sediment yield predictions via multiple endemic inputs, namely, climate, soil characteristics, topography, and LULC. Through the calculation of four parameters related to soil properties, namely, the effective hydraulic conductivity (ke), baseline critical shear stress (τc), baseline rill erodibility (kr), and baseline interrill erodibility (ki), the assessment of the initial run illustrates that calibration is inevitable. Given the geographical context and summer snowmelt dynamics, the model was unable to estimate summer runoff accurately. To address this problem, additional modeling for meltwater runoff was incorporated. The NSE and R2 values for discharge are 0.74 and 0.84, respectively, while those for sediment yield are 0.64 and 0.51, respectively. The results indicated that good predictions of runoff and sediment yield were obtained with the calibrated GeoWEPP model at the watershed scale. The key contribution of this research is the assessment of how eight biological conservation scenarios influence watershed behavior. Eight biological conservation scenarios were considered, representing incremental increases in canopy cover in poor, medium, and good pastures, both individually and in combination, as well as an additional scenario including expanded channel cover. The results showed that enhancing canopy cover could lower runoff and sediment yield by up to 44 % and 47 %, respectively, while the channel-cover scenario could lead to increases of up to 54 % and 67 %, respectively. These findings demonstrate the model's effectiveness in accurately replicating the hydrological and erosional responses resulting from soil and water conservation strategies.