退化沙质草地土壤种子库和地上植被对封育的响应机理

从植物种和植物功能类群两个水平系统探讨退化沙质草地土壤种子库和地上植被对短期封育管理响应机理的研究尚不多。以内蒙古东部的科尔沁沙地退化沙质草地为研究对象,采取随机样方法对禁牧6 a的封育区及与其相邻的自由放牧草地的土壤种子库和地上植物群落的物种密度进行了比较研究,草本植物群落被区分为一年生禾本科植物、非禾本科一年生植物和多年生植物3个主要功能类群。利用测定数据,分析研究了短期禁牧封育对土壤种子库和地上群落不同植物种和各植物功能类群的生态恢复作用机理。主要研究结果是：①短期封育显著促进了退化沙质草地植被的生态恢复,但发现土壤种子库和地上植被对禁牧的响应模式和机理存在明显差异,短期禁牧使土壤种子库中所有3个植物功能类群的密度均得到显著提高,而仅提高了地上植被一年生禾本科植物和多年生植物两个类群的密度;相反,禁牧显著提高了地上植被所有3个功能类群的物种丰富度和多样性,仅提高了土壤种子库中多年生植物类群的物种多样性。②短期禁牧显著增加了地上植物群落组成中可食和优良牧草的比例,提高了草地的经济利用价值。主要结论是：短期禁牧封育是一种经济有效的提高退化沙质草地植被多样性、生产力及对植物群落物种组成和草地品质进行优化调控和改良的重要草地管理手段。研究建议,今后应重点开展不同禁牧时间下对退化沙质草地土壤种子库和地上植被多样性、生产力及其物种组成变化影响的长期生态学控制实验研究。

Responses of Soil Seed Banks and Above-ground Plant Communities to Grazing Exclusion in a Degraded Sandy Grassland

How does grazing exclusion as an important grassland management strategy influence ecological restoration of soil seed bank and above-ground plant community in a highly degraded sandy grassland,and how do individual plant species, functional groups and community variables (i.e. diversity and density ) respond to grazing exclusion during the recovery process? In 2003, soil seed banks and above-ground plant communities in a fenced area (following 6-year grazing exclusion) and the grazed grassland next to the fenced area were investigated at 80 random locations in a highly degraded sandy grassland ecosystem. The grazing exclusion had a facilitative effect on recovery of the degraded grassland communities, but the facilitation varied remarkably between the seed bank and the above-ground community, as well as with different plant species, functional groups and community variables. Overall, the 6-year grazing exclusion resulted in significant increases of abundances in all three functional groups (i.e. annual grasses, non-grassy annals and perennials) in the seed bank, but caused only a significant increase in abundance of annual grasses and perennials in the above-ground community. In contrast, the grazing exclusion led to higher species richness and diversity in all three functional groups in the above-ground community, but caused a significant increase of only perennial species diversity in the seed bank. In addition, the grazing exclusion has also driven a change in floristic composition from a community dominated by the unpalatable species in grazed area to one dominated by the palatable species in fenced area. This study suggests that grazing exclusion can be used as an effective tool for conserving plant diversity and regulating community species composition, despite its differential effects on restoration of soil seed banks and above-ground plant communities during the recovery process.