降雨格局对库布齐沙漠土壤水分的补充效应

EFFECT OF PRECIPITATION PATTERN ON RECRUITMENT OF SOIL WATER IN KUBUQI DESERT,NORTHWESTERN CHINA

土壤水分是鄂尔多斯高原沙地油蒿（Artemisia ordosica）群落自发演替的重要驱动因子之一,其主要来源是大气降水。由于降水后总有部分水分被植物和表层土壤截留,随后很快蒸发,降水未能全部用于补充植物根系层土壤水分。减少的这部分降水不仅受年降水总量的影响,也与各次降水过程有密切的关系。因此,降水格局如何影响土壤水分的补充是探讨降水有效性、降水与植物群落关系需要解决的理论问题。该文从生态系统尺度出发,利用涡度相关技术,综合考虑生态系统水文平衡的各个环节,通过分析降雨、蒸散特征,对沙地土壤水分状况、生长季内降雨对土壤水分的补充进行了研究。结果表明,2006年全年降水总量229.4mm,以降雨为主。降雨、蒸散主要集中在5~10月,有效降雨约153.9mm,降雨效率68.9%。各次降雨的雨量、历时和强度等特征变异较大,降雨效率随雨量的增大而增大。降雨特征与其它生物和非生物因素相结合,影响生态系统蒸散及降雨对根系层土壤水分补充的有效性。5.0mm以下的降雨一般有增加空气湿度、降温的作用,一定程度上可以缓解旱情;5.0mm以上的降雨才能有效补充土壤水分,对植物群落长期稳定发展具有积极的意义。

Aims Soil water is one of the most important factors driving succession in the Artemisia ordosica community in the Ordos Plateau, an arid and semi-arid region of northwestern China. Precipitation is the main source of soil water on the sandland. During each rainfall, part of the rain water is intercepted by plants and the surface layer of soil. This usually quickly evaporates and seems to be biologically ineffective for plant life. Therefore, soil water recruitment is affected by both annual precipitation and characteristics of each rainfall event, such as amount and process. Our objective was to describe the dynamics of soil water content and water recruitment during the growing season. Methods We used eddy covariance technology to study the process of hydrological balance at the ecosystem scale and considered rainfall and evaportranspiration characteristics. Important findings In 2006, annual precipitation was about 229.4 mm and rainfall was the main form, mostly occurring from May to October. Rain events differed in rain amount, length of time and intensity. Ecosystem evaportranspiration and rainfall availability were clearly affected by these rain characteristics and other biotic and abiotic factors. Rain events 〈5.0 mm increased relative humidity and decreased temperature. Rain events 〉5.0 mm increased soil water in the root layer and were important to community development and stability.