吉首蒲儿根的繁殖生态学特性及其濒危成因

吉首蒲儿根为近年来发现的菊科蒲儿根属新物种,由于种群和数量都极度稀少,其濒危级别达极危(CR)等级。生态分布和生境的调查结果表明,吉首蒲儿根仅在吉首市德夯地质公园内分布有3个种群,总数约2000-3000株,其中,峡谷瀑布下的种群最大,约2000株;分布海拔为268-384 m,生境特点是温暖、湿润,土壤略偏酸性且钙质高。野外生殖物候的观察结果表明,2月初吉首蒲儿根的芽开始萌动,2月底至3月初抽生花葶,3月中旬至5月中旬开花,6月茎生叶逐渐枯死,随后根状块茎侧芽开始萌动,逐渐形成新分株。种群水平从第1个头状花序开放到最后一个凋谢约为50 d,单个头状花序从开始膨大到凋谢约为18 d,单朵小花的花期为3-5 d,整个过程表现出明显的雌雄异位和菊科特有的花粉次级展现现象。吉首蒲儿根的花部构成、高度同期的开花模式和"刷状机制"、瘦果小且无冠毛及以营养繁殖为主兼有种子繁殖等是对峡谷瀑布特殊生境的生态适应。人为活动的干扰,访花昆虫种类较少、访问频次和效率低,种子数量不多、质量差和传播不开,以及生境要求苛刻则是吉首蒲儿根致濒的主要原因。

The reproductive ecological characteristics of Sinosenecio jishouensis (Compositae) and its endangerment mechanisms

From a conservation perspective, understanding plant-pollinator interactions and floral biology of endangered species is critical in a rapidly changing world. Sinosenecio jishouensis D. G. Zhang, Y. Liu & Q. E. Yang is a new Asteraceous species (genus Sinosenecio) recently ascertained. According to IUCN Red Species List S. jishouensis ranked as the Critically Endangered Species (CR), for its extremely small and rare populations. However, little is known about the reproductive biology of this endangered species. Our results demonstrated that S. jishouensis occurred only in the Dehang Geological Park, Jishou City, Hunan Province. S. jishouensis distributed on an altitude of 260-340 m, and the environmental conditions were mildly warm and relatively humid. The yellow-red soil in its habitat, which was rich in calcium, has a pH value of about 6.8. There were totally 2000-3000 individuals distributed in 3 populations in the Dehang Geological Park, suggesting this species is at risk of becoming extinct. The Canyon Fall population was the largest one, with nearly 2000 individuals, which is an important population for conservation priorities. Its shoots began to sprout in Early Februray, and the scape appeared by the end of February or the early March; the flowering season was from mid-March to mid-May. S. jishouensis has herkogamy flowers with a 3-5d longevity. For a single capitulum, it could last 18 days. Secondary pollen presentation, a typical phenomenon in Asteraceae, were conspicuous during floret openning. Our observation suggested that Caliroa sawfly, Apis cerana and syrphid fly were the effective pollinators and visited flowers for collecting pollen. Our study indicated that floral structures, flowering synchronizatio, and "brush-like mechanism" were floral adaptations to improve the effective pollination. Furthermore, characteristics of its breeding system, such as small achenes without pappus and relying mainly on both clone production and sexual production, ensure reproductive success even when pollinators are scarce in the Canyon Fall special habitat. It may be adaptive strategies to the Canyon Fall special habitat. On the other hand, the human-made interference, the scarce flower-visiting pollination, low visiting frequency and efficiency, the small number of seeds with poor quality and dispersal, together with its strict demands on habitat conditions were the main causes for the rare and endangered status of S. jishouensis.