Vegetation primary production estimation at maize and alpine meadow over the Heihe River Basin, China

The accurate estimation of Gross Primary Production (GPP) is an important issue in carbon cycle studies. In this study, GPP dynamic of two typical vegetation in Heihe River Basin (alpine meadow in the upper stream and maize in middle stream) were estimated using Eddy Covariance (EC) and Vegetation Photosynthesis Model (VPM). Yearly GPP observed by EC at alpine meadow is 853 gC/m2/yr, which is only half of GPP of the value 1567 gC/m2/yr at maize field. This is mainly attributed to irrigation, fertilization and high light use efficiency at maize field. More than 80% carbon fixed by photosynthesis is release to atmosphere through ecosystem respiration at alpine meadow and at maize field 60%. The maximum light use efficiency of maize is 2.66 gC/MJ ARAR, while it is 1.6 gC/MJ ARAR at alpine meadow. VPM can correctly simulate seasonal dynamic and magnitude of GPP at both of the two sites. GPP values predicted by VPM were 872 gC/m2/yr at alpine meadow site and 1246 gC/m2/yr at maize site. The determination coefficients were as large as 0.9 at the alpine meadow site and 0.93 at the maize site. Average GPP value at each season predicted by VPM is very close to that observed by EC.