Effects of Waterlogging Stress on the Physiological Characteristics and Secondary Metabolites of Herbaceous Peony (<i>Paeonia lactiflora</i>Pall.)

Herbaceous peony is an ornamental plant with medicinal properties. Waterlogging can affect its yield and quality as it grows and matures. In this study, we subjected “Taohuafeixue”, “Yangfeichuyu” and “Hongxiuqiu” herbaceous peony varieties to a simulated waterlogging stress treatment and investigated the effects of waterlogging on their physiological characteristics and the secondary metabolite contents in their leaves and roots. Short-term waterlogging caused the leaves to turn yellow or red and the roots to turn black. The stele and the cell wall of the endothelial cells thickened, and the cortical cells enlarged. Waterlogging did not significantly change plant height, leaf length, and leaf area;however, it significantly decreased the root-shoot ratio of “Yangfeichuyu” and “Hongxiuqiu” varieties. The activity of antioxidant enzymes and the content of osmotic regulators increased under waterlogging. After short-term waterlogging stress treatment, the content of paeoniflorin and albiflorin increased in the roots of “Taohuafeixue” and “Yangfeichuyu”, and the content of benzoylpaeoniflorin increased in the root of “Hongxiuqiu”. The content of gallic acid and total flavonoids increased in the leaves of “Taohuafeixue” and “Yangfeichuyu”. After the waterlogging, paeoniflorin and benzoylpaeoniflorin increased in the autumn root of “Hongxiuqiu”. This study expands our knowledge about the medicinal properties of herbaceous peony and informs about its production and cultivation under waterlogged conditions.