Abstract: This research studied the changes (relative to unstressed plants) in the growth, osmotic adjustment and antioxidant system of Schizonepeta tenuifolia grown in pots under severe or moderate water deficit stress [substrate relative water content 5%-10% (severe stress), 45%-50% (moderate stress) or 85%-90% (no stress, CK)], imposed for a duration of 15, 30 or 45 days. The growth of S. tenuifolia showed increasing inhibition with increasing intensity of water deficit, with traits affected including the growth rate, leaf dry weight and total chlorophyll content, while leaf mass per area (LMA) increased under water deficit. Water deficit promoted the accumulation of osmotic adjustment substances in leaves, including soluble sugar, soluble protein, proline and Na⁺. Water deficit also generally increased the antioxidant capacity of leaves: The activities of superoxide dismutase (SOD) and catalase (CAT) were moderately increased at 15 and 30 days, but decreased at 45 days, relative to CK, while peroxidase (POD) activity was moderately increased at 30 and 45 days. The contents of total phenol and total flavonoids were moderately increased at 15 days, and reached their highest levels under moderate drought at 30 and 45 days. Increased duration of water deficit affected the osmotic adjustment in leaves: The soluble sugar and soluble protein contents increased; the proline, K⁺, Na⁺ and Ca²⁺ contents decreased; the activities of SOD and CAT increased initially and later decreased; POD activity continued to increase with time, and the accumulation of total phenols and total flavonoids increased initially and then remained unchanged. In summary, S. tenuifolia made adaptive responses to drought stress and showed tolerance to moderate drought. This study provides a theoretical basis for the standardized cultivation and water management of S. tenuifolia.

Key words: Schizonepeta tenuifolia, drought stress, osmotic adjustment, antioxidant capacity