Energy And Water Budget Of A Poplar Plantation In Suburban Beijing

Eddy-Covariance (EC) open path system, Sap flow method, soil water balance method and microclimate monitor system were employed in this study to investigate energy balance and water budget at the different spatial and temporal scales in growing season of 2005～2006.The study site is locates in DaXing district Beijing with on sandy soil conditions and 11-year-old stand Poplar plantation.The primary goal was to estimate the energy components contribution and energy closure level, the dynamic process of evapotranspiration and its components under different soil water status and respond to the environmental factors.We also compared the ET total based on the eddy covariance and soil water balance method.Field data suggested that the energy closure level was more higher at growing season scale and the variation of energy partitioning contribution was quite great in different soil water conditions.A analyse of energy balance show that the ratio of Hs/Rn is higher during dry period than that under moist condition, which indicated the most of energy was used for evapotranspiration when soil water was sufficient in such ecosystem.Under water stress, the net radiation and soil factors play the important role to ecosystem evapotranspiration. The transpiration rate is lower than that of soil evaporation before the rain season, however, with the deep layer soil water content becoming more wet following the rain events, the transpiration rate is more higher, meanwhile the soil evaporation rate went down greatly. There was a similar result of evapotranspiration total in the growing season based on the soil water balance and sap flow method.And soil water balance method had a little overestimate for evapotranspiration total relative to the EC method.The evapotranspiration and transpiration had a more higher correlation with net radiation and vapour pressure deficit in wet days than that of dry days.The MIKE SHE model performed well at a sandy poplar plantation ecosystem in north China, the model simulations could capture the dynamics of the soil water content and evapotranspiration process.