三峡濒危植物疏花水柏枝的回归引种和种群重建

疏花水柏枝分布于三峡库区原海拔70～155m的消落带,三峡工程修建后它将丧失其全部生境而成为濒危植物。实验结果显示其种子在土壤含水量大于10%以上时开始萌发,以土壤含水量达到饱和状况时萌发最好。种子萌发与定居阶段对土壤水分条件的严格要求使得疏花水柏枝分布区十分狭小。回归引种和种群重建是拯救该物种的主要手段。三峡工程修建后库区内新的消落带将形成夏旱冬淹的水节律,完全不同于库区原有消落带所具有的冬旱夏淹的水节律,不适于作为疏花水柏枝种群的迁移地。相比之下库区淹没区以上各支流消落带的生态环境与疏花水柏枝原有生境较为接近,适于作其新的生境。种群遗传多样性、年龄结构、分布格局、繁殖与扩展等生物学特性是种群持续发展的基础,文章以此为依据,对疏花水柏枝种群重建与管理中的相关问题进行了分析讨论。认为疏花水柏枝种群恢复与重建中目前所面临的主要问题是如何增强被隔离的种群间的基因交流、促进种群的种子扩散与萌发、协调新建种群与当地物种的关系、营造有利于新建种群定居与生长的生态环境。重建种群的管理应结合疏花水柏枝的生长发育节律和移栽地的生态环境条件来开展,要有效地监控种群的生长发育动态,合理地在隔离种群间相互引种,适时地进行水分管理,并对周围植被适度控制。

Reintroduction and population reconstruction of an endangered plant Myricaria laxiflora in the Three Gorges Reservoir area, China

Myricaria laxiflora occurs in the flood zone from 70 to 155 m above sea level along the Yangtze River in the Three Gorges Reservoir area. Its natural distributional range is very narrow and restricted. The species lost almost all of its habitats and became endangered when the water level of the Three Gorges Reservoir was raised to 140 m in June 2003 as a result of the construction of the Three Gorges Dam for hydro-electricity generation. Therefore, the Three Gorge Project Construction Committee of the State Council funded a program to save Myricaria laxiflora by artificially establishing five populations of the species in four branches of the Yangtze River in the Three Gorges area in 2002. The transplanted populations established successfully. We surveyed these populations every two months and conducted ecological experiments in order to understand the factors limiting the distribution of Myricaria laxiflora, and to evaluate the reintroduction sites and arrangement, ecological environment amelioration, and population transplantation and management of Myricaria laxiflora. Result showed that seed of Myricaria laxifloram could not germinate when water content was below 10% for sandy soil and 15% for sandy loam soil. Optimal seed germination occurred on the soil with saturated water. The restricted distribution of the species in flood zone along the river is therefore most likely due to the limitation of water content of upland soil during seed spread and germination. All natural habitats of this species would be submerged when the water level is raised to 175 m as planned. When the dam is completely finished, which makes in situ conservation in the future flood zone impossible. Reconstruction of the populations ex situ would be the only approach to preserve the species. The flood zone above 175m in branches of the Yangtze River, which has the similar ecological landscape and environment to the original habitats of Myricaria laxiflora, might be the suitable sites for population reconstruction even though the community compositions and structures there are different. The populations of Myricaria laxifloram are a metapopulation. Three to 9 year-old plants from different populations were transplanted to reconstruct artificial populations in order to conserve genetic biodiversity and maintain population viability. The sizes of all reconstructed populations were bigger than 1000 considering the seedling loss from flood and drought. Vegetation on the sites for population introduction were partially cut and cleared before transplantation took place in order to avoid species competition. Seedlings were planted on the middle flood zone to match seedling requirements for water and avoid flood washing. The reconstructed populations were irrigated after transplantation and in the dry seasons to facilitate seedling establishment and growth. Artificially exchanging germplasm among the reintroduced populations in different branch rivers and the establishment of reproduction system by establishing several populations along a river branch are necessary in future to resolve the problem of population isolation and facilitate genetic exchanges.