The effect of progressive drought on physiological traits of Scutellaria baicalensis Georgi

【Objective】 Scutellaria baicalensis Georgi (SBG) is a Chinese medicine. This paper studies the combined effect of initial soil water content and progressive drought on physiological traits and quality of SBG. 【Method】 The pot experiment was conducted in a mobile water shelter. The initial soil water content in the pots were controlled at 40%, 60% and 80% of the field capacity (FC) to represent severe, moderate, and mild drought, respectively. In each treatment, we measured the biomass, photosynthetic characteristics, osmotic substances, activities of antioxidant enzymes and active ingredients of the plants. 【Result】 ① No significant difference in biomass accumulation was found between the treatments. ② During the stress period, baicalin content was significantly higher in the 80%FC treatment, baicalein content was significantly higher in the 40%FC treatment and the baicalin content decreased with initial soil water treatment in the order of 40%FC>60%FC>80%FC. When the soil water content was 40%FC and 60%FC, the baicalin content was 17.3% and 11.3% higher than that when soil water content was 80%FC. Change in soil water contents did not have a significant impact on baicalein content. ③ Net photosynthetic rate, transpiration rate, stomatal conductance and intercellular carbon dioxide concentration all decreased as the plants grew, regardless of the soil water treatments. 8-10 d after the onset of water stress, the net photosynthetic rate did not show significant differences between the 60%FC and 80%FC treatments. ④ Under water stress, the content of malondialdehyde and proline in all treatments increased as the plants grew. The proline content was the highest in the 80%FC treatment, reaching 121.66 μg/g. ⑤ The activities of POD and CAT responded to water stress similarly, both increasing gradually as water stress persisted. The impact of soil water on activity of SOD was ranked in the order of 40%FC>60%FC>80%FC. ⑥ The active ingredients were higher in the 40%FC and 60%FC treatments. 【Conclusion】 Severe progressive drought with the soil water content kept at 40%FC reduced photosynthesis and increased baicalein content, osmolytes and activity of antioxidant enzymes. Mild and severe droughts by keeping the soil water content at 40%FC and 60%FC can improve accumulation of active ingredients in SBG.