| Using the data getting from long-term experiments in situ,the calculating method of plant coefficients for arbors and shrubs in gully-hilly region of the Loess Plateau was studied in this paper,the actual evapotranspirations and mean soil water contents during the growing season for two representative arbors(Ulmaceae propinque and Populus simonii) and two representative shrubs(Caraganna korshinskii and Hippophae rhamnoides) were compared,and the impacts of soil water content fluctuations on plant roots absorbing soil water and soil water availability were analyzed.The results showed that,in this experimental region,the actual evapotranspirations of shrubs are less than that of arbors while there are no obvious differences between the same plant types.The plant coefficient of Ulmaceae propinque was the minimum among the studied plants,Caraganna korshinskii's was the second and Hippophae rhamnoides's was the maximum.The soil water availability to the four plants had no notable distinction.But both the plant coefficients and soil water restriction should be considered in calculation of vegetation ecological water requirement and selection of drought-resistant plant variety in arid area. |