Abstract: Super hybrid rice variety Tianyou 998 was pot-cultured in climate chambers to study the characteristics of its flag leaf photosynthesis and chlorophyll fluorescence parameters at four growth stages (heading, milking, waxmaturing, and full maturing) under high temperature stress. Five high temperature treatments were installed. The maximum temperature was installed at 32, 35, 38, 40, and 42  ℃, respectively, with a 6  ℃ difference per day, and each treatment was lasted for 5 days, 2 hours per day, and taking the natural condition as the control (CK). High temperature had obvious effects on the characteristics of the flag leaf photosynthesis and chlorophyll fluorescence parameters, and the effects differed with the high temperature treatments, rice development stages, and test items. The higher the temperature, the greater the effects were. After treated with high temperature, the test items such as chlorophyll content (SPAD), net photosynthetic rate (P_n), stomatal conductance (G_s), efficiency of PSII photochemistry (F_v/F_m), actual quantum yield (Φ_PSII), apparent photosynthetic electron transport rate (ETR), photochemical quenching coefficient (q_P), and photochemical reaction (P) decreased, while the intercellular CO₂ concentration (C_i), initial fluorescence (F_o), nonphotochemical quenching coefficient (q_N), and other heat dissipation (E) increased. Most of the photosynthetic and chlorophyll fluorescence parameters at the four growth stages changed significantly when the maximum temperature was above 35  ℃, and decreased greatly when the maximum temperature was above 38  ℃. At heading and milking stages, the P_n and G_s had a significant decrease while the C_i had a significant increase; at wax and full maturing stages, the SPAD decreased significantly. The decrement of the F_v/F_m and the decrement of the F_o were greater at heading and milking stages than at wax and full maturing stages. High temperature stress had greater effects on the P_n than on the SPAD. The decrease of the P_n at heading and milking stages was mainly induced by the stomatal factors, while the P_n decrease at wax and full maturing stages was mainly caused by the no-stomatal factors.

Key words: re-vegetation, soil biological crusts, nitrogenase activity, nitrogen fixation, hydrothermal factor.