Abstract: Through a longterm observation on wheat canopy temperature,it was found that in the nature,there existed low temperature wheat germplasm (LTWG) with constant low canopy temperature,and high temperature wheat germplasm (HTWG) with constant high canopy temperature.The study on the leaf structure and some physiologic characteristics of LTWG during its blooming and milk-filling stages showed that the canopy temperature of LTWG was 1～4 ℃ lower than that of HTWG.The mesophyll cells of LTWG functional leaves were smaller,more compact in cell arrangement,and 1～2 cell layers more than those of HTWG’s.The average thickness of three LTWG functional leaves was 166,192 and 165 μm,being 26 μm thinner than that of HTWG,average vein interval of three functional leaves was 257,231 and 245 μm,being 31 μm smaller than that of HTWG,average transverse area of big veins of three functional leaves was 5 961,6 580 and 5 603 μm²,being averagely 837 μm² more than that of HTWG,and average transverse area of small veins was 1 624,1 521 and 1 472 μm²,being averagely 246 μm² more than that of HTWG.The chlorophyll content of three LTWG functional leaves was 2.8749,2.8162,and 2.4129 g·100 g^-1 FW,net photosynthetic rate was 10.864,10.8003,and 10.1939 μmol·m^-2·s^-1,and transpiration rate was 0.0076,0.0074,0.0067 mol·m^-2·s^-1,respectively,which were all higher than those of HTWG.It was revealed that there were close relationships among canopy temperature,organ structure,and physiologic function.

Key words: equilibrium time, soil texture., soil water isotope, extraction method, plant water source segmentation