Physiological Characterization under the Influence of Drought Stress and Salicylic Acid in Valeriana wallichii DC

Abstract Valeriana wallichii DC, a high-altitude medicinal plant, is highly sensitive to drought stress, which adversely impacts its physiological functions and root biomass. This study aimed to evaluate salicylic acid’s role in mitigating drought stress by assessing physiological and biochemical responses in V. wallichii . Plants were treated with foliar applications of SA at concentrations of 0.25, 0.50, 0.75, and 1.0 mM during vegetative and flowering stages. Physiological parameters such as photosynthetic rate, stomatal conductance, water use efficiency (WUE), intrinsic WUE (iWUE), carboxylation efficiency, and biochemical traits including chlorophyll and carotenoid content were measured, alongside fresh and dry root biomass.Drought stress significantly reduced photosynthetic performance (Pn) (3.95 μmol CO 2 m□ 2 s□ 1 at 25% FC), stomatal conductance, relative water content, and root yield. SA application notably improved these traits. At 25% FC, 1.0 mM SA enhanced WUE (28.78), iWUE (642.37 μmol/mol), and fresh root weight (8.41 g). Under moderate drought (50% FC), 0.50 mM SA improved net photosynthesis (12.5 μmol CO 2 m□ 2 s□ 1 ), dry root weight (2.31 g), and chlorophyll content. SA treatments also stabilized membrane integrity and maintained higher chlorophyll fluorescence efficiency (Fv/Fm).These findings demonstrate that foliar application of SA enhances drought tolerance in V. wallichii by improving photosynthetic efficiency, water relations, and root biomass. The study supports the strategic use of SA to improve the resilience and productivity of medicinal plants under drought stress conditions. Highlights of the study Drought lowers growth and yield by reducing photosynthesis and water use. Salicylic acid reduces drought effects and improves plant performance. At severe drought, 1- 0.50 mM SA raised WUE, conductance, and root yield. Under mild drought, 0.75- 0.50 mM SA improved gas exchange and yield. SA doses 0.25-1 mM differ in effectiveness across drought stress stages.