Abstract: The water use dynamic of Leymus chinensis population,which is the dominant species in Leymus chinensis steppe,was studied in its whole growing period in 1998.Neutron probe,photoelectric apparatus and LI1600 steady state porometer were used.The population's and single leaf's transpiration rate,on day scale,are mainly affected by soil moisture in the 20-40 layer(SW40,%w/w),photosynthesis active radiation(PAR,w·m²)and day average atmosphere temperature(AT,℃).As this equation the forecasting function,transpired water everyday was calculated and further the water use effciency(WUE)dynamic,in the whole growing season,was gotten.It was proved that the dynamic of WUE in the whole growing season,was accord to plant growth cycle,that is,in the early period,when plant actively grew,the WUE was high,whereas it was low in the later stage when the biomass accumulation became slow.

Key words: Leymus chinensis, WUE, Transpiration, Water use dynamic,Seasonality

摘要： 采用中子水分探测仪、光电叶面积仪和LI-1600型稳态气孔计对羊草草原的水分利用进行野外实验观测。结果表明,羊草种群蒸腾速率T(t)的季节变化主要取决于20-40cm土层贮水量(SW46),光合有效辐射(FAR)和大气日均温(AT)的影响,其中20-40cm土层贮水量对羊草蒸腾速率的季节变化影响最大。羊草蒸腾耗水量的季节动态归根结底受控于大气降水的时空分布,并在时间上滞后于大气降水一旬左右。羊草的水分利用率,主要受植物生长大周期的控制。生物量在前期积累较快,相应的水分利用率高,而后期增长缓慢,水分利用率低。

关键词: 羊草种群, 蒸腾速率, 蒸腾量, 水分利用效率, 季节动态