Different from GPP and
ET, the variation of WUE in spring was not evident. However,
WUE peaked in July/August during the period of the growing season,
with the values ranging between 2.45 and 2.87 g C kg1 H2O.
The reason was that stoma closed under higher temperature in
summer and transpiration rate declined more than photosynthesis
rate, leading to the increase of WUE (Maroco et al., 1997). After
October, as the decline in air temperature, GPP and ET dropped
gradually. In winter, the growth of the mixed plantation stopped
and GPP and ET dropped the lowest values. Nevertheless, WUE
was not low.