Modeling the maximum apparent quantum use efficiency of alpine meadow ecosystem on Tibetan Plateau

The net CO2 exchange between the atmosphere and an alpine meadow ecosystem (NEE) was measured by Eddy covariance technique in Damxung county (30°25′N, 91°05′E, 4333 m a.s.l.), Tibet, China for three continuous growing seasons from 2003 to 2005. The apparent quantum use efficiency (α) of alpine meadow was derived based on the linear function between NEE and photosynthetically active radiation (PAR) under low light. A model driven by the main ecological factors, such as temperature, CO2 concentration was further adapted for α modeling at stand level. The key parameter of this model was the maximum apparent quantum use efficiency (α0), which could be inversed with the model. As a parameter for the growth status of a plant community, α0 changed in accord with leaf area index (LAI), and the maximum for alpine meadow was about 0.016 μmol CO2 μmol−1 PAR. If considered by the soil moisture (θ), α0 was linearly correlated with θ when the soil moisture was lower than 0.2 m3 m−3, and α0 leveled off gradually when θ was higher than 0.2 m3 m−3. This model provides a method to simulate α at stand level and can be applicable to different communities. When the CO2 concentration is double in the future, the α of alpine meadow will increase by 7%, and the tendency might be strengthened by the global warming.