宁夏六盘山3种典型植物群落水分利用特征及其组分的季节变化

为深入认识干旱缺水区水通量分配和植被类型变化对群落水分利用特征的影响，在宁夏六盘山叠叠沟小流域，利用热扩散技术、微型蒸渗仪、树干径向变化记录仪及文献资料等方法研究了三种典型植物群落的蒸腾（T_r）、蒸散（ET）和水分利用效率（WUE）及组成的季节变化。结果表明:生长季三种植物群落ET（mm）为:华北落叶松林（429.7） > 沙棘林（379.3） > 草地（206.9），分别大于、约等于、小于同期的降雨量，均呈现低—高—低的月变化趋势。冠层蒸腾是蒸散的主要分量，生长季T_r/ET为:华北落叶松（48%） > 沙棘（39%）；华北落叶松林T_r/ET随季节持续降低，沙棘林T_r/ET随季节先升高后降低，最大为50.4%。生长季WUE（g/kg）为:草地（3.1） > 华北落叶松林（2.7） > 沙棘林（2.35）。其中，华北落叶松林WUE变化与其T_r/ET月变化相同，从WUE在林分各层的分布来看，乔木层WUE为4.04 g/kg，草本层为1.36 g/kg；沙棘林WUE表现为生长季前、中期较高而后期较低的变化趋势，其中灌木层WUE为2.32 g/kg，草本层WUE为2.37 g/kg；草地WUE在生长季前、中期均保持在3.2~4.8 g/kg。研究表明:无论是在水分充足季节（生长季中期），还是水分有限季节（生长季初期和末期），植被不可能完全利用所有的降水，但水分利用特征存在种间差异。

The Water Use Characteristics of Three Representative Plant Communities and their Seasonal Variation in Liupan Mountains,Ningxia

To understand the characteristics of water use of vegetation and the relationship between water use and community structures in dryland, three typical types of vegetation including Larix principis-rupprechtii plantation, Hippophae rhamnoides plantation and natural grassland were selected to estimate the seasonal variations of transpiration (T_r), evapotranspiration (ET), water use efficiency (WUE) and their partitioning of vegetation by using thermal dissipation technique, micro lysimeter, dendrometer and document literature in the Diediegou catchment of Liupan Mountains, Ningxia. The results indicated that the ETs of three types of vegetation during the growing season arranged as:L. principis-rupprechtii forest (429.7) > H. rhamnoides forest (379.3) > grassland (206.9), respectively, greater than, almost equal to, less than the same period of rainfall. The total ETs of three types of vegetation showed a low-high-low seasonal trend. The T_t/ET ratios of two planted forests had remarkable difference with the order of L. principis-rupprechtii forest (48%) > H. rhamnoides forest (39%). The T_r/ET ratio of H. rhamnoides forest had the similar seasonal pattern with its ET, the highest was observed in September(50.4%), but the T_r/ET ratio of L. principis-rupprechtii forest decreased over time during the growing season. The order of the WUE of three types of vegetation during the growing season followed as:grassland (3.1 g/kg) > L. principis-rupprechtii plantation (2.7 g/kg) > H. rhamnoides plantation (2.35 g/kg). The WUE of L. principisrupprechtii forest decreased over time during the growing season. The WUE of tree layer of L. principisrupprechtii forest was 4.04 g/kg, while that of herbaceous layer was only 1.36 g/kg. The WUE of H. rhamnoides forest showed a high value in the early and middle of growing season, but a low values in the later growing season. And WUE of the shrub layer was 2.32 g/kg, while it was 2.37 g/kg for herbaceous layer. WUE of the natural grassland ranged 3.2 ~ 4.8 g/kg from May to August, then decreased to 0 in September. It is implied that plants do not use all of the precipitation input not only in water-sufficient season (the early and late stage of the growing season), but also in water-limited season (the medium stage of the growing season), and also showed interspecific difference.