CONTRASTING CHANGES OF CHLOROPHYLL FLUORESCENCE IN LEAVES OF INVASIVE WEDELIA TRILOBATA AT ROOM OR LOW TEMPERATURE UNDER HIGH IRRADIANCE STRESS

The effects of low (10℃) and room ( 25℃) temperature on chlorophyll- fluorescence parameters were investigated in the leaves of the alien invasive Wedelia. trilobata and its native congener Wedelia chinensis under high irradiance (1700molm-2s-1) in order to explore the ecological adaptability of the invasive species to low temperature under high irradiance conditions. The results were as follows: the decreases of the maximum quantum efficiency of photosystem II photochemistry (Fv/Fm), the effective PSII quantum yield (Yield) and the apparent electron transport rate (ETR) in W. trilobata were significantly lower than those in W. chinensis after 5h of high irradiance treatment at room temperature, while the decreases of those chlorophyll-fluorescence parameters in the former were significantly higher than those of the latter in the high irradiance treatment at low temperature. Our preliminary results indicated: (1) the invasive species W. trilobata have a greater adaptability to high irradiance stress at room temperature and is susceptible to high irradiance stress at low temperature; (2) the invasive species W. trilobata are more adaptive to the high temperature and high irradiance climate in tropic and subtropical regions of South China; and (3) low temperature is one of possible environmental limiting factors for its spreading further into the North China.