极度濒危植物贵州大花杜鹃的濒危机制解析

Highly species diversity of Rhododendron occurs in Guizhou and moreover many rhododendrons are currently endangered there. However no detailed conservationresearch and conservation actions have been performed till now in Guizhou. The present study is aiming to clarify factors contributing to the high risk extinction to Rhododendron magniflorum with the largest flowers and critically endangered species listed in the red list of rhododendrons, by combining methods in field investigation, reproductive ecology and conservation genomics. Specifically two hypothesis causing extinction of R. magniflorum is proposed respectively: 1) as so large flowers what is the effective pollinators for the target species? Are these pollinators seriously influenced in the currentfragmented populations? 2) what are roles of both past demography and contemporaryhabitat disturbance contributing to the formation of small populations and acceleration of extinction to R. magniflorum? Our results will aid to decide effective conservation strategies for R. magniflorum and meanwhile shed light on reference for other plant conservation in Guizhou.

贵州具有丰富的杜鹃花资源，其中不乏特有的珍稀濒危物种。本项目选择杜鹃属花冠最大、贵州特有的极度濒危（CR）物种贵州大花杜鹃（Rhododendron magniflorum）为研究对象，在系统的野外居群调查、繁殖生态学与种群遗传结构解析基础上，重点回答导致其极度濒危的两个假说：① 作为花冠如此大的杜鹃，其有效传粉者是什么？严重破碎化的生境是否抑制其授粉与结实的有效性？② 物种的濒危是过去种群历史与当代人为破坏的共同作用结果，那么对贵州大花杜鹃而言，这两者的相对贡献如何？本研究结果有助于科学的制定贵州大花杜鹃的保护策略，同时为贵州省其它濒危植物的保护提供借鉴。

本项目通过对贵州省特有的极小种群植物贵州大花杜鹃野外调查，共发现4个野生种群。其中，龙头大山成年植株数量最少，不足10株。小草坝种群次之，不足50株。六盘水及九龙山种群最多，但仍然不足100株。野外贵州大花杜鹃幼苗更新困难，几乎看到不到幼株。通过花特征与传粉生物学研究发现：贵州大花杜鹃异交为主，部分自交亲和；其有效传粉者为白额鹰翅天蛾，主要靠花的气味（主成分芳樟醇占到总成分的76%）吸引。种子传播与萌发实验可以说明种子自身传播和萌发的能力不是导致贵州大花杜鹃种群稀少的原因。但厚重的凋落物会延缓与阻碍种子掉落到土壤，而直接掉落到凋落物上会降低贵州大花杜鹃种子发芽率。最后，基于简化基因组测序（RAD-seq）的方法对贵州大花杜鹃保护基因组做了深入分析，发现贵州大花杜鹃在杜鹃花属植物中维持居中的遗传多样性水平，不同种群间遗传分化差异明显。基于种群遗传特征、私有等位基因以及种群遗传结构的综合结果，提出了贵州大花杜鹃有针对性的保护策略。