Abstract: To explore the effects of nocturnal low temperature on photosynthesis of Coffea liberica and Coffea arabica,the two dominant coffee species in Southern Yunnan,the potted seedlings were exposed to nocturnal low temperature (4℃) for 3 days and then recovered for another 3 days under ambient environment during the cool and foggy season of Xishuangbanna in 2003.The photosynthesis parameters and the content of H₂O₂ and MDA were measured in mature leaves of the two species.The results showed that after three day's nocturnal low temperature exposure,although thermal dissipation capacity (NPQ) and Car/Chl ratio increased,the net photosynthetic rate (Pn),stomatal conductance (Gs) and initial photochemical efficiency of photosystem II (Fv/Fm) at dawn decreased greatly in leaves of the two species,accompanied with the accumulation of H₂O₂ and MDA,which suggested that their photosynthetic apparatuses were destroyed,and both stomatal and non-stomatal limitation contributed to the decrease of net photosynthetic rate.There were no significant differences of photosynthetic ability between the two coffee species in normal conditions.But compared to C.liberica,C.arabica had less decrease of Pn and Fv/Fm,less accumulation of MDA after nocturnal low temperature exposure,and recovered more quickly than C.liberica.That means that C.arabica is more chilling-tolerant than C.liberica.The mechanism is related with its higher Car/Chl ratio,heat dissipation capacity and higher ability to recover.

Key words: Fly ash, Adsorption capacity, P adsorption rate, P desorption rate