Soil Amendment With Bentonite Modulates Physiological and Biochemical Traits to Mitigate Drought Effects in Summer Savory Under Greenhouse Conditions

Summer savory ( Satureja hortensis L.) is a valuable annual herb sensitive to drought stress. This greenhouse study investigated whether amending soil with natural bentonite clay (0, 50, or 100 g kg ^-1 ) could mitigate the effects of three irrigation regimes (100, 75 and 50% of field capacity, FC). Growth, physiological and biochemical parameters were measured using a factorial based on completely randomized design to assess plant respons. Results showed that severe drought (50% FC) reduced shoot biomass by 25.8% and leaf relative water content (RWC) by 37.2%, while increasing root growth and oxidative stress markers (malondialdehyde by 50.8%). Bentonite amendment at 50 g kg ^-1 significantly alleviated these stress symptoms: it restored leaf RWC by 42.4% in stressed plants, increased the activity of key antioxidant enzymes (guaiacol peroxidase and polyphenol oxidase) by up to 45.5% and enhanced the uptake of essential nutrients (e.g., N, K, Zn). Consequently, this optimal bentonite rate improved the biomass of drought-stressed plants by up to 19.0%. The higher application rate (100 g kg ^-1 ) was less effective or even detrimental, likely due to reduced soil aeration. Our findings demonstrate that moderate bentonite application (50 g kg ^-1 ) effectively enhances drought tolerance in summer savory by improving soil water retention, nutrient availability and the plant’s antioxidant capacity. This strategy offers a practical and sustainable approach to cultivate this high-value medicinal herb under water-limited conditions.