The Variations Of Water Use Efficiency And Evapotranspiration Over A Plantation In The Southern Part Of Hilly Areas Of North-china

In this paper, Water vapor and carbon flux from 2007 to 2009 was contiuously measured by eddy covariance technque over a 30 years old mixed plantation (XLD) in a hilly area of the North China at Jiyuan city, Henan Province. The variations of water use efficiency (WUE) and evapotranspiration were studied. The main conclusions included,1. During 2007 to 2009, the ecosystem appeared as a carbon sink. The annual average NEE and GPP were -418.08 gCm-2y-1 and 1349.57 gCm-2y-1 gCm-2y-1. The annual water vapor flux (Fw) and WUE were 556.65 kg·m-2·y-1 and 2.71mg·g-1.2. Fw of the growing seaon was 3 to 4 times higher than that of the non-growing season, and accountied for about 78% of the whole year. Carbon uptake in growing season was about 30 times higher than that in non-growing season, accounting for about 97% of the whole year. WUE was highest in winter, and lowest in summer. During the three years, the mean WUE were 2.5mg·g-1 in growing season, and 3.0 mg·g-1 in non-growing season. Affected by the rainfall in January 2009, WUE reached maximum about 8.14 mg·g-1.3. There was a positive correlation between Fw and net radiation (Rn) at XLD. Under different weather conditions, the correlation coefficient of Rn and Fw was around 0.3. The relationship between GPP and photosynthetic active radiation (PAR) was linear. Fw and GPP increased exponentially with temperature, and WUE was not relevant with temperature. The relationship of Fw and GPP with the vapor pressure dificit (VPD) showed a quadratic curve. GPP, WUE was positively correlated with LAI.4. Atmospheric drought restriction on evapotranspiration (ET) was greater than that on photosynthesis. ET and GPP increased with LAI.