Diurnal conditions, genetic background, and climatic factors, together with within-plant microenvironments, can alter the accumulation of secondary metabolites, leading to variability in plant volatile oils (VOs). In this study, the effects of time of day and vertical canopy position on VO yield and chemical profile were investigated in Salvia rosmarinus Spenn. (syn. Rosmarinus officinalis L.) leaves at the onset of flowering. Leaves were collected at 06:00, 12:00, and 18:00 from the lower, middle, and upper thirds of the canopy; composite samples were prepared per canopy stratum and sampling time, hydrodistilled, and analyzed by GC–MS. VO yield showed a clear positional pattern, increasing from the lower to the upper canopy across all sampling times, and ranged from 0.43% to 0.75% (v/w, DW basis). Overall, 71 constituents were identified, and the number of detected compounds varied across treatments (55–68), with the lowest richness observed in the upper third at midday. Across all samples, the VO profile was consistently dominated by oxygenated monoterpenes and monoterpene hydrocarbons, whereas sesquiterpene-related fractions exhibited more pronounced time- and stratum-dependent variation. Among major constituents, camphor remained prominent but varied substantially (6.71–15.59%), with a marked minimum in the middle third at midday and a maximum in the upper third in the morning. Other abundant constituents also showed treatment-dependent redistribution, including cis-verbenone (10.48–17.94%), borneol (8.60–12.79%), α-pinene (4.91–11.61%), and 1,8-cineole (5.77–9.55%). These findings indicate that both harvest time and canopy sampling height are key determinants of S. rosmarinus VO yield and compositional consistency, underscoring the need for standardized harvest specifications when composition-oriented profiles are targeted.
Soltanbeigi et al. (Sat,) studied this question.