Response of canopy quantum yield of alpine meadow to temperature under low atmospheric pressure on Tibetan Plateau

An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux from July to October, 2003. The canopy quantum yield (alpha) of alpine meadow was calculated by the linear function between the net ecosystem carbon dioxide exchange (NEE) and the photosynthetic active radiation (PAR) under low light, and how it was influenced by the temperature was also discussed. Results showed that the canopy a decreased almost linearly with temperature, with the decrease in every 1 degrees C increase of temperature similar to those measured on leaf level of C-3 plant. At the beginning, the decrease of canopy a with temperature was 0.0005 Nmol CO2-mu mol(-1) PAR; while it increased to 0.0008 Nmol CO2.mu mol(-1) PAR in September, showing a rising trend with plant growing stages. Compared with the canopy a calculated with rectangular hyperbola function, the value in the paper was lower. However, the method advanced here has the advantages in examining the relationship between a and the key environmental factors, such as temperature.