Abstract: With 5℃ Night temperature treatments for 13h each day, net photosynthetic rate(Pn), stomata conductance(Cs), inter-cellularCO₂ concentration(Ci), transpiration rate(Tr), water use efficiency (WUE) and chlorophyll content(Ch1) of one year Rhizophora stylosa and Heritiera littoralis seedings Leaves were measured after 1h and 4h recovery at greenhouse temperature.The results showed that Pn, Cs, Tr and WUE of Rhizophora stylosa and Heritera littoralis seedings leaves were significantly inhibited by low night temperature treatments but Ci were raised and Ch1. had litter changes. Pn、Cs and Tr of two mangrove species would rise as recovering times increased, which indicated that both Rhizophora stylosa and Heritiere littoralis seedling had some adaptation to low night temperature, when low night temperature treatment days increased, Pn and Tr of Rhizophora stylosa were more inhibited than Heritiera littoralis. A linear relationship existed between Pn and Cs and between Tr and Cs, respectively, which showed that carbon gain by photosynthesis and water loss by transpiration were inhibited at the same time.It is suggested that Cs was the main factor to control dynamic balance between carbon gain process and water loss process.

Key words: mangrove, low night temperature, net photosynthetic rate, transpiration