Response of Dahlia Photosynthesis and Transpiration to High-Temperature Stress

The high temperature may cause difficult growth or bloom in the summer, which is the key problem limiting the cultivation and application of dahlia. The photosynthetic physiological mechanisms of dahlia under high temperature stress were studied to provide a theoretical basis for expanding the application range of cultivation and annual production. Two dahlia varieties, 'Tampico' and 'Hypnotica Tropical Breeze', were used as test materials and were treated for 1 d or 2 d at temperatures of 35/30 degrees C or 40/35 degrees C (day/night: 14 h/10 h) and then recovered at 25/20 degrees C for 7 d. A 25/20 degrees C treatment was used as the control. The results are as follows: (1) High-temperature stress resulted in the chlorophyll (Chl) content, Fv/Fm, transpiration rate (Tr), net photosynthetic rate (Pn), and water potential decreasing significantly, and the Chl content, Tr, and stomatal density of 'Tampico' were higher than those of 'Hypnotica Tropical Breeze' during the same period. (2) After the two dahlia varieties were treated with high-temperature stress and recovered at 25/20 degrees C for 7 d, the plant morphology and various physiological indices under the 35/30 degrees C treatment gradually returned to normal, with 'Tampico' in better condition than 'Hypnotica Tropical Breeze'. (3) Both dahlia varieties could not withstand the stress of 40/35 degrees C for 2 days.