The Tibetan Plateau is characterized by lower atmospheric pressure, lower air temperature and high daily and seasonal variation due to high elevation. The photosynthesis of plants is significantly influenced by these alpine environmental factors. Apparent quantum yield (αA) is one of the basic parameters of photosynthesis and mass production. Its accuracy determination is of significance to model photosynthesis of C3 plants and global change on the plateau. In the Lhasa Plateau Ecological Station with 65.4 kPa of atmospheric pressure at an elevation of 3688 m, Li-Cor 6400 portable photosynthesis system was used to measure light response curves of winter wheat in different temperatures and intercellular CO2 concentration (Ci).The slope of light response curve in weak light area of PFD from 0 to 150 μmol m-2 S-1 was used to evaluate the value of αA. The dependence of αA on temperature and intercellular concentration was analyzed. In 30℃, the average value of αAWaS 0.0476 ± 0.0038. It is not quite different from the values in low elevation areas. αA is influenced both by temperature and by the ratio of CO2and O2 partial pressure ([CO2]/[O2]). The measured values in the previous study were much lower.This might be due to systematic errors from instrument and data processing methods. The values of αA decreased linearly with temperature. It decreased 0.0007 in every 1℃ increase of temperature. The decrease slope is similar to those of C3 plants in the previous researches. While [O2] is constant, αA increases with Ciwith a hyperbolic relationship. In comparison with low elevation areas, the αA on the Tibetan Plateau is more sensitive to increase of CO2.
