荒漠草原向灌丛转变过程两种优势植物定植土壤水分阈值特征

为探究宁夏东部荒漠草原灌丛转变过程中两种优势种蒙古冰草（Agropyron mongolicum）和柠条锦鸡儿（Caragana korshinskii）植物更新土壤水分需求特征，在前期萌发土壤水势阈值研究的基础上，进一步通过野外观测和室内干旱胁迫试验分析确定转变过程中两种优势植物种的定植土壤水分阈值。结果表明：荒漠草原灌丛近30年人为转变过程中0-200 cm土壤水分呈降低趋势，灌丛地土壤水分含量较荒漠草地显著降低了52.43%（P<0.05），灌丛转变加速了土壤旱化；柠条锦鸡儿和蒙古冰草幼苗定植过程中叶绿素含量随干旱胁迫程度加深呈先增加后降低趋势，其死亡率逐渐上升。通过渗透势和死亡率的拟合函数以及其对应样地的土壤水势、土壤水分关系分析得出，随样地转变柠条锦鸡儿定植土壤水势、水分阈值均低于蒙古冰草，两者平均土壤水势阈值分别为-9.38—-9.95 kPa、-8.72—-9.28 kPa，平均土壤水分阈值分别为4.93%-5.23%、5.92%-6.50%。与蒙古冰草相比，柠条锦鸡儿更适应灌丛引入下或降雨减少引起的土壤旱化，其旱生条件下的定植成功更易发生。

Characteristics of soil moisture threshold for the seedling establishment of two dominant plants in desert grassland-shrubland transition

In order to explore the characteristics of soil moisture avilability for plant recruitments of the two dominant species Agropyron mongolicum and Caragana korshinskii in desert grassland-shrubland transition of eastern Ningxia, the soil moisture thresholds of the two plant species were caculated by conducting field observations and drought stress experiments based on the previous study on the soil water potential threshold for germination. The results showed that soil moisture in the depth of 0-200 cm soil has been decreasing during the transition from desert grassland to shrubland over the past 30 years, and the soil water content of shrubland was significantly lower than that of desert grassland by 52.43% (P<0.05), that is, shrub introduction had accelerated the process of soil drought. With the process of the seedling establishment of Caragana korshinskii and Agropyron mongolica, the chlorophyll content firstly increased and then decreased with the drought stress increase, meanwhile the mortality rate gradually increased. The fitting function of osmotic potential and mortality and soil water characteristic curves of the transitional sites were used to determine the soil water potential and soil moisture thresholds for seedling establishment of the two plant species. The results showed that the soil water thresholds of Caragana korshinskii were all lower than those of Agropyron mongolica in each transition site, and the average soil water potential thresholds of the two species were -9.38--9.95 kPa, -8.72--9.28 kPa, and the average soil moisture thresholds were 4.93%-5.23%, 5.92%-6.50%, respectively. In summary, compared with soil water acquirement of Agropyron mongolica, Caragana korshinskii is more adapted to soil drought caused by shrub introduction and climate change to recruit more successfully.