中文摘要：

水是北方农牧交错带最关键的生态环境因子,水资源与生态环境之间的相互关系和相互影响很大程度上决定了北方农牧交错带的环境状况与环境动态。文章从生态缺水的角度,以内蒙古自治区武川县为例,探讨了生态系统退化机理,为北方农牧交错带的生态恢复与重建提供科学依据。研究结果表明,生态缺水是造成北方农牧交错带植被生态系统退化的主要原因。2006年武川县天然草地、灌木、乔木、农作物生长季平均耗水量分别为150.3mm、193.4mm、213.3mm、158.6mm,最小生态缺水量分别为93.1mm、38.2mm、251.5mm、96.6mm,植被生态系统继续向退化方向演替。合理调整植物品种结构,配置有限的水资源是当地生态恢复与重建的紧迫任务。

英文摘要：

The issues of ecological water requirements have already been a focus of research in the context of increasingly aggravated eco-environment. The ecological water requirement is defined as the water capacity needed by the ecosystem which achieves a certain ecology level or maintains a certain dynamic balance status. The ecological water requirement would be different for different regions and different ecological objectives. Water is the most critical ecological factor over the northern farming-pastoral zones in China. The interrelations and interactions between water and the eco-environment to a large extent dictate the environmental dynamics and status of the northern farming-pastoral zones. In the present work, the authors investigated the mechanisms of the degradation of ecosystems from a perspective of ecological water shortage, with the aim to provide meaningful reference for ecological restoration and reconstruction in the northern farming-pastoral zones. The vegetation ecological water requirements for the Wuchuan County, a typical dry and semi-arid agro-pastoral transitional zone located in the middle part of the northern ecotone and facing serious ecological degradation, were calculated with the Penman-Monteith equation. In addition, the status of ecological water shortage in Wuchuan County was analyzed in detail on the basis of the experimental data of vegetation ecological water consumptions. The results showed that the major reason for degradation of vegetation ecosystems in the northern ecotone was ecological water shortage. The average water consumptions of natural grassland, shrubbery land, arbor land and cropland in Wuchuan County during growing season in 2006 were estimated to be 150.3 mm, 193.4 mm, 213.3 mm and 158.6 mm, respectively. The smallest amounts of ecological water shortage were estimated to be 93.1 mm, 38.2 mm, 251.5 mm, and 96.6 mm, respectively. It was found that vegetation of the ecosystem continued to develop towards the direction of degradation. Reasonable adjustments for the str