4. Conclusions
Based on 5-year experiment data, we analyzed the variations of
GPP, ET and WUE and discussed the mechanisms of climatic variables
and soil moisture controlling GPP, ET and WUE in a warm temperate
mixed plantation. At the monthly scale, GPP and ET
had similar relations with solar radiation, air temperature, VPD
and precipitation, indicating that the variety in climatic variables
drove photosynthesis and evapotranspiration at the approximately
same rate. In the vigorous growing season, WUE decreased significantly
with the augment of VPD and solar radiation. GPP was
greater but ET lower under cloudy skies than that under sunny
skies. Consequently, WUE was 29–72% more under cloudy sky conditions
in comparison with that under sunny sky conditions. During
the period from 2006 to 2010, annual average WUE ranged
from 1.76 to 2.41 g C kg1 H2O. The interannual variation in WUE
was mainly controlled by soil water content.