珍稀沙生植物茧荚黄耆的繁殖特性与种群更新的关系研究

The research on the relationships between the reproduction characteristics and population recruitment of rare plants can play an important role in revealing their threatened mechanism theoretically. The reported studies on plant population recruitment mainly focus on seed source, dispersal features and seedling establishment, little is known about the effects of reproduction characteristics on the population recruitment. Astragalus lehmannianus is a rare desert species of Astragalus (Fabaceae) that is distributed narrowly in the southern margin of the Gurbantunggut Desert of northern Xinjiang. In this project, we select Astragalus lehmannianus as a target species, and A. flexus, a sympatric cosmopolitan species of Astragalus, as a contrast species. Based on the investigation of the distribution regions, the assessment of the threatened status and the ascertainment of the endangered category of A. lehmannianus, we will focus on the researches about the relationship between the floral syndrome and the reproduction success and seeds dispersal, the influence of herbivores on reproduction and the relationship between seed germination and seedling establishment, analyze the impact of the special floral syndrome on reproduction assurance and the enhancement of seed dispersal ability of this species, explore the effects of herbivory and seed abortion on seed source and seedling establishment, explicit the type of seed dormancy, the type of soil seed bank and the environmental condition of seed germination and seedling establishment, reveal the biotic and abiotic factors that restrict the population regeneration. These results will not only provide theoretical and technical guidance for revealing the threatened factors and developing the strategies of population recovery and conservation of A. lehmannianus, but also accumulate theoretical information for exploring the diversity of ecological adaptation of desert plants.

珍稀植物繁殖特性与种群更新的关系研究对于揭示其致危机制具有重要的理论价值。已有的植物种群更新研究主要集中在种源特性、传播特性及幼苗建成等方面，而有关繁育特性对种群更新的影响还少见报道。茧荚黄耆是狭域分布在新疆北部古尔班通古特沙漠南缘的豆科黄耆属珍稀物种。本项目拟以茧荚黄耆为研究材料，并以同域广布种弯花黄耆为对照种，在分布区调查、受胁状况评估及濒危等级确定的基础上，重点研究花部综合征与繁殖成功及种子传播的关系、植食昆虫对繁殖的影响以及种子萌发与幼苗建成的关系，分析其特殊花部特征在保障繁殖及提高传播能力中的作用，探讨植食作用和种子败育式样对种源特性和幼苗建成等的影响，明确种子休眠和土壤种子库类型以及种子萌发和幼苗建成的环境条件，揭示限制种群更新的生物与非生物因子。研究结果不仅可为揭示茧荚黄耆的致危原因、制定种群恢复与保育策略提供理论和技术指导，还可为探讨沙生植物生态适应的多样性提供理论资料。

茧荚黄耆是我国仅分布于新疆古尔班通古特沙漠固定和半固定沙丘上的珍稀豆科植物，已被列入新疆第一批重点保护的野生植物名录。本项目拟以茧荚黄耆为研究材料，在分布区调查、受胁状况评估及濒危等级确定的基础上，重点研究了花部综合征与繁殖成功及种子传播的关系、植食昆虫对繁殖的影响以及种子萌发与幼苗建成的关系。研究结果表明：(1)茧荚黄耆属于极危物种；其“蚕茧状”花萼的存在不仅有利于有性繁殖，还可提高种子的扩散能力并防御植食昆虫食花。(2)过度放牧、土地利用、工程建设和旅游等人类活动可能是导致茧荚黄耆濒危的直接原因，而传粉者限制所造成的近交衰退以及荒漠极端环境和气候变化所造成的种群更新困难可能是该物种致危的间接因素。(3)茧荚黄耆的果实存在受遗传控制的选择近柱头端种子败育式样。该式样可使母株将更多资源分配给正常发育的种子，以提高种子质量，促进种群更新。(4)昆虫啃食种皮能显著提高种子的吸水速率并快速打破物理休眠，使被啃食种子提前萌发。其中，种子被轻度啃食或啃食子叶虽对幼苗存活和生长的影响较小，但可增加被啃食同龄种子同时萌发所导致的竞争风险；而种子被中/重度啃食、啃食胚根或同时啃食子叶和胚根可严重影响幼苗存活与生长，二者均不利于种群更新。(5)茧荚黄耆的遗传变异主要来自于居群内的遗传差异，居群间的遗传分化程度并不高。这些研究结果不仅为茧荚黄耆的种群恢复与保育提供了理论和技术指导，还为探讨沙生植物生态适应的多样性积累了理论资料。