Gas exchange and chlorophyll a fluorescence transient were examined in leaves of sorghum under salt stress and high temperature. During salt treatment with 50 and 150 mm NaCl, photosynthetic rate (Pn) decreased, which could be ascribed to stomatal limitation. Salt stress had no effect on photosystem II (PSII) activity. At high temperatures, PSII function was inhibited in leaves of sorghum, indicated by the decrease in PSII performance index on absorption base and PSII maximal photochemistry efficiency (Fv/Fm); however, the decrease was lower in salt‐treated sorghum, suggesting that salt adaption enhanced heat tolerance of PSII. The enhanced heat resistance can be expressed on all the components of PSII including reaction centre, donor side and acceptor side. Consistently, a slight decrease in Pn was found in salt‐treated sorghum at high temperatures, indicating that salt adaption also enhanced heat tolerance of photosynthesis. Proline plays an important protective role in plant response to environmental stress, and its large accumulation in salt‐treated sorghum might be the underlying reason leading to the enhanced heat tolerance. As for this pattern of photosynthetic response, sorghum seems to be a reliable crop species for human beings in the face of global warming and increasing salinity of agricultural land.

Gas exchange and chlorophyll a fluorescence transient were examined in leaves of sorghum at high temperatures. No changes were found in photosynthetic rate (Pn) and photosystem II (PS II) performance index on absorption base (PI(abs)) at 40 °C for 1 h. But transpiration rate was enhanced significantly, which served as a self‐protection response for dissipating heat. The Pn decreased significantly at 40 °C for 3 h, and the decrease became greater at 45 °C. Decrease in Pn mainly resulted from stomatal limitation at 40 °C for 3 h, whereas it was due to non‐stomatal limitation at 45 °C. Decline in PS II function indicated by the significant decrease in PI(abs), trapped energy flux and electron transport flux were responsible for the decrease in Pn at 45 °C. PS II reaction centre and oxygen‐evolving complex in the donor side were not affected at high temperatures, but electron transport in the acceptor side was sensitive to high temperature. The PS II function recovered completely 1 day after high temperature stress even as high as 45 °C, which is favourable for sorghum to meet the challenge of global warming. However, Pn did not completely recover possibly due to heat‐induced irreversible damage to CO2 fixation process.