Physiological and metabolic responses of dill to nano-silica and nano-zinc under drought stress: implications for yield and essential oil quality.

Nano-silica (Si) and nano-zinc (Zn) are increasingly used to mitigate drought stress, yet their combined effects on both plant physiology and essential oil (EO) characteristics in dill (Anethum graveolens L.) under field conditions remain insufficiently characterized. This study assessed whether nano-Si and nano-Zn improve drought responses and EO composition in dill over two growing seasons (2023–2024). A split-plot design with three replications was employed, with irrigation regime as the main-plot factor and nano-fertilizer treatments as subplots; year was included as a factor in a combined statistical model. Drought stress reduced net photosynthesis (Pn) by 53% and seed yield by 38%, while increasing oxidative stress indicators (MDA, H₂O₂, electrolyte leakage) by 85–120% compared with irrigated plants. Under drought, high-dose nano-Si and nano-Zn treatments increased Pn by 60–70% and seed yield by 32–36% relative to the drought control, alongside 30–40% lower oxidative damage markers and higher proline levels. EO composition also differed among treatments, with several monoterpene and phenylpropanoid constituents showing 20–65% higher relative abundance under drought with nano-fertilizer application. Responses of several traits varied between seasons, reflecting treatment × year interactions rather than confirmed cumulative effects. These results demonstrate that nano-Si and nano-Zn were associated with improved physiological performance and altered EO profiles in dill under the tested conditions. However, mechanistic interpretation is limited to physiological and biochemical indicators, and findings are restricted to one species, location, and set of application rates. Further multi-environment studies and evaluation of environmental safety are needed before broader agronomic application.