Studies on the Physiological Response of Sedum hybridum Cutting Seedlings to Drought Stress

Sedum hybridum presents high drought resistance. In this study, the physiological indexes of S. hybridum cutting seedlings were investigated in the 60 days of drought stress, including leaf relative water content, malondialdehyde (MDA) content, cell damage rate, photosynthetic parameters (net photosynthetic rate, stomatal conductance and transpiration rate), fluorescence parameters (F_v/F_m, q^P, PHiPS2), malic acid content and phosphoeno-lpyruvate carboxylase (PEPCase) activity. Results showed that drought stress led to a decrease in leaf relative water content, photosynthetic parameters and fluorescence parameters, and an increase in cell damage rate and MDA content. Within the first 30 days of drought stress, the physiological indexes exhibited small amplitude variation. After 40 days of stress, the variation amplitude of physiological indexes increased rapidly. In the following experiments, malic acid content and PEPCase activity increased significantly, demonstrating that the C₃ pathway was weakened and crassulacean acid metabolism (CAM) pathway was stimulated, which was involved in the stress response of S. hybridum to enhance drought resistance. After 60 days, stress exceeded the tolerance range of S. hybridum plants, leading to serious damage and gradual death. Our results showed that S.hybridum cuttings exhibited strong drought tolerance physiologically, and possessed the characteristics of a facultative CAM plant. Activation of the CAM pathway enhanced drought tolerance, which was an important mechanism of S.hybridum.