羊草群落的水分利用

羊草(Leymus chinensis (Trin．)Tzvel．)群落的土壤水分具有明显的成层性：O-40cm是根系集中分布层，受降水和蒸散的直接影响，称为蒸散与降水相互作用层；40-120cm贮水变化滞后于根系层贮水和群落蒸散的季节变化，称为主要贮水层；120cm以下称为水分相对稳定／平衡层。1996年属平水年，生长季末土壤水盈余18mm；1998年属丰水年，在连续强降雨时发生渗漏，生长季末土壤水亏缺15mm。蒸腾-蒸散比(T/ET)不仅反映群落的繁茂和活力，而且反映植物对环境水资源的利用状况。1998年8月T/ET值较小(0．5)，6月达O．7，7月受降水少影响而有所降低(O．6)，8月水分利用效率达到最大(O．9)，9月降到O．6。水分利用效率(WUE)在良好的水分条件下(1998年)，主要受植物自身生长速度的限制，其季节变化与生长大周期吻合。深入分析WUE和T/ET的内涵，提出蒸散效率(ETE)的概念，能更好地反映植物对环境水资源利用的状况或程度，具有实际意义。

Water Use of Leymus chinensis Community

Soil moisture of Leymus chinensis (Trin.) Tzvel. community has obviously stratified phenomena:the layer (0-40 cm) in which roots are concentrically distributed is directly influenced by precipitation andevapotranspiration. It can be called interaction layer of precipitation and evapotranspiration. The layer(40-120 cm), where water-storage capacity exchange lagged exchange of the root-layer water-storagecapacity and the community evapotranspiration, can be called major water-storage layer. The layer (under120 cm) can be called water relatively stable/balanced layer. The year 1996 was a normal flow year, and soilwater had a surplus of 18 mm at the end of the growing season. The year1998 was a high flow year, becauseleakage took place under continuous heavy rainfall, soil water had a deficit of 15 mm at the end of thegrowing season. Transpiration to evapotranspiration (T/ET) value reflected not only the luxuriance degreeof the community, but also the water use regime of the environmental resources. T/ET value was low(0.5) in May 1998, reaching 0.7 in June, then decreasing to 0.6 in July, due to the impact of rainfallinclining, while August reached the maximum (0.9), and September decreased to 0.6. Water use efficiency(WUE) was mainly restricted by the growing rate of plants under sufficient water condition (1998). Itsseasonal changes were coincident with the grand period of growth of the plants. When both meanings ofWUE and T/ET were analyzed profoundly, the concept of evapotranspiration efficiency (ETE) which can all-side reflect utilization regime of the environmental water resources was advanced.