Stress alleviators improve root yield phytochemical composition and enzymatic activity in echinacea purpurea under...

Drought stress is one of the most critical environmental constraints limiting the growth and medicinal quality of plants cultivated under hydroponic systems. This study evaluated the potential of foliar-applied amino acids, pure potassium, and potassium silicate as stress alleviators for mitigating drought-induced damage in Echinacea purpurea grown under hydroponic conditions. Plants were subjected to three drought levels (0, - 2, and - 4 bar induced by polyethylene glycol), and their morphological traits, phytochemical composition, antioxidant capacity, enzymatic activities, nutrient status, and essential oil content were assessed. Drought stress significantly reduced root number, root fresh weight, and root length by approximately 39%, 52%, and 37%, respectively, compared with non-stressed plants. Foliar application of stress alleviators markedly alleviated these negative effects. Total phenolic and flavonoid contents increased by up to 58% and 74%, respectively, under potassium and potassium silicate treatments compared to the control. Antioxidant defenses were strongly enhanced under drought stress, with potassium silicate increasing superoxide radical scavenging activity by 16.7% and ascorbate peroxidase activity by 24% under severe stress conditions. Although drought stress reduced nitrogen, phosphorus, and potassium uptake, foliar application of stress alleviators partially restored nutrient levels. Essential oil content was also enhanced, showing an increase of up to 8.7% following potassium and potassium silicate application. Overall, foliar application of stress alleviators contributed to the mitigation of drought-induced physiological and biochemical damage in E. purpurea. Among the tested treatments, potassium silicate showed the greatest efficacy, highlighting its potential as a practical and efficient strategy to enhance root yield, antioxidant defense, and medicinal quality of hydroponically grown Echinacea under water-limited conditions.