Effect Of Low-temperature On Photosynthesis Of Several Tropical Plants In Xishuangbanna

To explore the effect of nocturnal low temperature on ecophysiological characteristics of Coffea liberica and Coffea arabica, the two dominant coffee species in Southern Yunnan, their potted seedlings were treated with nocturnal low temperature (4 ℃) for 3 days and recovered for another 3 days during the cool and foggy season of Xishuangbanna in 2003. The photosynthetic characteristics and the content of H2O2 and MDA were measured on mature leaves of two species. The result showed that, after three day's nocturnal low temperature treatment, although thermal dissipation capacity (NPQ) and Car/Chl ratio increased, the net photosynthetic rate (Pn), stomatal conductance rate (Gs) and initial photochemical efficiency of photosystem II (Fv/Fm) at dawn decreased greatly in leaves of both coffee species, along with increases of of H2O2 and MDAcontents. These suggested their photosynthesis apparatuses were injuried, and both stomatal and non-stomatal limitation contributed to the decrease of photosynthetic rate. Before the chilling treatment, there were no significant differences of photosynthetic characteristics between the two coffee species. But comparing to C. Liberica, C. arabica had the less decrease of Pn and Fv/Fm and the less accumulation of MDA after nocturnal low temperature treatment, and recovered more quickly than C. liberica.The above results revealed that C. arabica was more chilling-tolerant than C. liberica, with the mechanism was probably related with its higher Car/Chl ratio and heat dissipation capacity.To explore the effect of seasonal low temperature on tropical fruit trees, photosynthesis and protective enzyme activities in leaves of Artocarpus altilis, Artocarpus heterophyllus and Garcinia mangostana, which were introduced from tropical areas and are sensitive to low temperature, were measured during the rainy and the foggy and cool seasons in Xishuangbanna, SW China. The maximal net photosynthetic rates of three fruit trees were lower in the foggy and cool season than in the hot and rainy season. A. altilis and G. mangostana had a larger decrease in maximal net photosynthetic rate than A. heterophyllus. Diurnal photoinhibition of A. altilis and G. mangostana were intensified during the foggy and cool season. Activities of protective enzymes (SOD, CAT, POD) increased in foggy and cool season, but MDA still accumulated. This indicated that the physiology of these three fruit species were adversely affected by the seasonal low temperature. Lower decrease of maximal net photosynthetic rates and chlorophyll content, lower diurnal photoinhibition, less accumulation of MDA and higher activities of SOD, CAT and POD showed less effect of seasonal low temperature on A. heterophyllus that had a stronger resistant ability to low temperature than A. altilis and G. mangostana.