In this study,the gas exchange,chlorophyll fluorescence and antioxidant activity in tall fescue cultivar,Houndog 5 ,were investigated under long-term high temperature stress. The results showed that the net photosynthetic rate (Pn),chlorophyll content,apparent quantum yield (AQY),the maximum carboxylation rate of Rubisco (V c,max ),the maximum rate of RuBP regeneration (J max ) and carboylation efficiency (CE) were significantly decreased after treatment with high temperature for 30 d. High temperature also decreased the efficiency of excitation capture by open PSⅡ reaction centers (F’v/F’m) and the proportion of open PSII reaction centers,thereby resulting in an increased electron transport flow (ETR). The non-photochemical quenching (NPQ) and energy-dependent quenching (qE) of the tall fescue were significantly decreased,and the excess energy of PSII reaction centers (Ex) was largely increased after long-term high temperature stress. Moreover,high temperature stress significantly decreased the SOD,POD,APX and GR activities,and increased the MDA content. These results indicated that the mechanism of excitation energy dissipation and antioxidant systems were injured,so that the excessive excitation energy could not be dissipated and reactive oxygen species could not be scavenged efficiently.
