Abstract: Effects of four temperatures (35 , 40 , 45 and 50 ℃) on photosynthetic rate (Pn) , concentration of internal leaf CO2 (Ci) , stomatal conductance ( Gs) , transpiration rate ( Tr) and chlorophyll fluorescence in sweet pepper were studied. The results showed that when plants were treated with 35 and 40 ℃, Pn decreased with the decreasing of Ci . When plants were treated with 45 and 50 ℃, Pn decreased considerably , Ci changed slightly at 45 ℃and increased at 50 ℃. Changes of Gs were positively correlated with Tr. It could be concluded that inhibition of photosynthesis at extreme high temperature stress resulted from nonstomatal limitations , but stomatal limitations lead to inhibition of photosynthesis when plants were under mild high temperature stress. The change of transpiration was more sensitive to stomatal conductance than photosynthesis. Fluorescence parameters such as Fv/ Fm ,
Fo and Fm were hardly changed under 35 and 40 ℃, but Fv/ Fm and Fm were reduced , Fo was increased at 45 and 50 ℃. After recovery at 25 ℃for 24 hours , Fo , Fm and Fv/ Fmwere almost entirely restored. The results suggested that reversible inactivation of PSII is the main factor leading to photosynthetic inhibition under short terms of high temperature stress.

Key words: Pepper, High temperature stress, Photosynthesis, Chlorophyll fluorescence