| Poplar plantation is one of the most predominant plantations in northern China.It is widely used as timber production stand, ecological services plantation or landscape afforestation. Because of its water-cosumed characteristics, the tradeoffs betweenwater consumption and mannual poplar plantation growth in arid and semi-arid areas has attracted many researchers’ attention. To compare the plantation water balance in different growing periods, as well as to analyze the relationships between water balance components and environmental factors are very essential to realize the sustainable management of poplar plantation. In this study, three methods-sap flow, eddy covariance and soil water budget-were used to evaluated evapotranspiration. Moreover, meteorological and soil moisture observation were all taken into account to analyze water balance. The results showed that:(1) during the growing season in2010～2012, the major water revenue of this poplar plantation wes rainfall. Interannual rainfall varied greatly, and the rainfall distribution in one year was also quite uneven for most rainfall accurred during growing season. And most rainy days’precipitation was less than10mm.(2) The daily trend of single tree’s sap flow mainly showed a bell curve but this curve would change under different weather conditions. In addition, in different period of growing season, the maximum value of daily sap flow and the timing of sap flow beginning to turn up and down were various. The water consumption of single tree grew with the diameter at breast height (DBH). Compared the results of previous study of this site and other sites, daily transpiration of single tree was relatively low in our study.(3) inter annual stand transpiration were of great difference, and during growing season in2010～2012the value were113.7mm,174.6mm and192.1mm respectively. There was a positive correlation between stand transpiration and net radiantion and vapor pressure deficit within a certain range. However, if the net radiation or vapor pressure deficit was over high, the increasing stand transpiration would be inhibited. Meanwhile, the relationship between stand transpiration and net radiation and vapor pressure deficit changed with the soil moisture.(4) Soil evaporation were155.4mm,209.8mm, and153.2mm respectively during the2010～2012growing season and the monthly soil evaporation was also uneven in different month. The soil heat and moisture condition was the main factor that affected soil evaporation. The soil water storage was nearly0in2011and2012growing season.(5) Through the results of energy closure test, we confirmed that the eddy covariance data was confident. The stand evapotranspiration measured by eddy covariance tower in2010～2012growing season were361.9mm,490.5mm and552.8mm. This result was much the same as that of soil water budget method but was a bit lower than that of sap flow method.(6) On the stand scale, the water input and output could reach a balance and even had a slight surplus. Evapotranspiration was the major water output in this study, and its main components were transpiration, soil evaporation and canopy interception. Soil evaporation shared the largest proportion of stand evapotranspiration, and transpiration was slightly less than soil evaporation. Canopy interception was the smallest portion of evapotranspiration. |
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