Effects Of High Temperature And Drought Stress On Physiological And Biochemical Characteristics Of Four Hydrangea Cultivars

This study had used four Hydrangea varieties as experiment materials,which are Hydrangea.macrophylla'Sabrina',H.macrophylla'Taube',H.macrophylla'Endless Summer Bride',and H.paniculata'Pink Fantasy'.Through the artificial high temperature and drought test in summer in Zhejiang Province,the response mechanism of Hydrangea to high temperature and drought stress was studied from the aspects of physiological characteristics,photosynthesis and chlorophyll fluorescence characteristics,which provided a basis for the study of new resistance varieties of Hydrangea.The main results are as follows:?1?The soluble sugar content of the four Hydrangea cultivars increased under high temperature and drought single stress and compound stress,the soluble protein content decreased at normal temperature and moderate temperature,and increased first and then decreased under severe high temperature.The POD activity,CAT activity and APX activity of different varieties of Hydrangea increased first and then decreased under high temperature and drought stress,while SOD activity varied with temperature and drought course.The production rate of superoxide anion and the content of hydrogen peroxide in the four varieties of Fydrangea increased and then decreased,and the content of MDA continued to rise.?2?The net photosynthetic rate of four varieties of Hydrangea decreased with the increase of photosynthetically active radiation with the increase of drought stress or temperature stress.The maximum photosynthetic rate,apparent quantum efficiency,and dark respiration rate of Hydrangea decreased with the increase of stress under high temperature and drought stress.‘Pink Fantasy'has a relatively high light saturation point and a minimum drop,indicating that it has better adaptability to high temperature and drought.?3?In single stress and compound stress,the net photosynthetic rate and stomatal conductance of different Hydrangea decreased with the increase of stress,and the transpiration rate decreased first or then decreased first,then rose and decreased.The intercellular CO₂ concentration decreased in the interphase and increased in the late stress stage,indicating that the photosynthetic obstruction of Hydrangea in the early stage of high temperature and drought stress was mainly due to stomatal limitation,and the inhibition of Hydrangea photosynthetic inhibition under severe stress was a non-stomatal limiting factor.?4?The initial fluorescence of the cultivars increased continuously under single stress and compound stress,and the maximum photochemical efficiency and actual photon yield decreased with the increase of high temperature and drought stress.The actual photon yield was the smallest after severe combined stress,indicating that the combined stress significantly reduced the activity of PSII reaction center.The non-photochemical quenching coefficient of each variety increased first and then decreased with the increase of compound stress,and the photochemical quenching coefficient decreased with the increase of stress,it indicated that the high temperature and drought stress led to the decrease of the openness of the different varieties of Hydrangea PSII reaction center,photosynthetic function was protected by increasing the NPQ dissipation of excess light energy.?5?After comprehensive evaluation,the tolerance of four varieties of Hydrangea under high temperature and drought stress was ranked from strong to weak:‘Sabrina'>‘Pink Fantasy'>‘Endless Summer Bride'>‘Taube'.