Rosemary is a hardy Mediterranean plant known for its essential oils, but its growth and chemical profile can still be affected by severe environmental stress.

*   **Drought Stress:** Controlled drought stress can have a minimal impact on overall growth but alters the essential oil composition.
*   **Biomass under Drought:** Severe drought can lead to a decrease in the development of fresh biomass.
*   **Essential Oils under Drought:** Drought stress generally leads to an increase in the production of essential oils as a defense mechanism.
*   **Terpene Composition:** Drought can increase the percentage of terpenes like bornyl-acetate and β-caryophyllene, while decreasing α-pinene.
*   **Salt Stress:** Salinity is a major environmental stress that limits the growth and productivity of rosemary.
*   **Salinity and Vegetative Growth:** Increasing soil salinity levels discernibly reduces plant height and total herb dry weight.
*   **Salt Resistance Index (SRI):** The SRI decreases with increasing salinity.
*   **Chlorophyll:** Total chlorophyll in leaves is reduced by higher soil salinity.
*   **Proline Content:** Salinity enhances leaf proline content as an osmoprotectant.
*   **Volatile Oil Percentage:** Irrigation with saline water can have a significant effect on the volatile oil percentage.
*   **Volatile Oil Composition:** Salinity alters the chemical makeup of the essential oil; for example, the major constituent camphor can be affected.
*   **Amino Acid Application:** Applying amino acids like L-tryptophan and glutamine can improve plant growth, chlorophyll content, and salt resistance under salinity stress.
*   **Antistress Agents:** The application of agents like salicylic acid and diatomaceous earth can improve vegetative growth and volatile oil percentage in plants under salt stress.
*   **Combined Salinity and Amino Acids:** The combination of amino acid application with low-to-moderate soil salinity can enhance the Salt Resistance Index to over 100%.
*   **Water Stress from Irrigation Type:** The type of irrigation water (tap water vs. saline water) and rainfed conditions (non-irrigated) create different stress levels, affecting essential oil yield and composition.
*   **Essential Oil Yield:** Rainfed (non-irrigated) conditions can result in the highest essential oil yield, while irrigation with saline water results in the lowest.
*   **Anti-stress Effects (Internal):** Rosemary leaf extract has been shown to have anti-stress effects in animal studies, alleviating stress-induced dysfunctions, which points to the plant's complex chemical response to its environment.
*   **Location and Cultivar Influence:** The effects of drought stress on biomass and essential oil yield are significantly influenced by the growing location and the specific rosemary cultivar.
*   **Suitability for Marginal Land:** Its general tolerance suggests rosemary is suitable for cultivation in marginal soils to protect against erosion and diversify crops.