Department of Plant Ecology, Albrecht von Haller Institute of Plant Sciences, University of Göttingen, Göttingen, Germany.
Plant Biol (Stuttg). 2011 Nov;13(6):857-64. doi: 10.1111/j.1438-8677.2011.00452.x. Epub 2011 Mar 1.
Habitat fragmentation and reduction of population size have been found to negatively affect plant reproduction in 'new rare' species that were formerly common. This has been attributed primarily to effects of increased inbreeding but also to pollen limitation. In contrast, little is known about the reproduction of 'old rare' species that are naturally restricted to small and isolated habitats and thus may have developed strategies to cope with long-term isolation and small population size. Here we study the effects of pollen source and quantity on reproduction of the 'old rare' bumblebee-pollinated herb, Astragalus exscapus. In two populations of this species, we tested for pollen autodeposition, inbreeding depression and outbreeding depression. Caged plants were left unpollinated or were pollinated with pollen from the same plant, from the same population or from a distant population (50 km). Additionally, we tested for pollen limitation by pollen supplementation in four populations of different size and density. In the absence of pollinators, plants did not produce seed whereas self-pollinated plants did. This indicates a self-compatible breeding system dependent on insect pollination. Both self-pollination and, in one of the two populations, cross-pollination with pollen from plants from the distant population resulted in a lower number of seeds per flower than cross-pollination with pollen from plants from the resident population, indicating inbreeding and outbreeding depression. Pollen addition enhanced fruit set and number of seeds per flower in three of the four populations, indicating pollen limitation. The degree of pollen limitation was lowest in the smallest but densest population. Our results suggest that, similar to 'new rare' plant species, also 'old rare' species may be at risk of inbreeding depression and pollen limitation.
生境破碎化和种群数量减少已被发现会对以前常见的“新稀有种”植物的繁殖产生负面影响。这主要归因于近交增加的影响，但也归因于花粉限制。相比之下，对于那些自然局限于小而孤立栖息地的“老稀有种”的繁殖情况知之甚少，因为它们可能已经发展出了应对长期隔离和小种群数量的策略。在这里，我们研究了花粉源和数量对受熊蜂授粉的稀有草本植物 Astragalus exscapus 繁殖的影响。在该物种的两个种群中，我们测试了花粉自沉积、近交衰退和远交衰退。对笼养植物进行了未授粉或自授粉处理，所用花粉来自同一植株、同一种群或相距 50 公里的遥远种群。此外，我们还在四个不同大小和密度的种群中测试了花粉补充对花粉限制的影响。在没有传粉者的情况下，植物无法产生种子，而自花授粉的植物可以产生种子。这表明它具有依赖昆虫传粉的自交亲和繁殖系统。自交和在两个种群中的一个种群中与来自遥远种群的植物的花粉杂交，都会导致每朵花的种子数量比与来自定居种群的植物的花粉杂交时少，表明存在近交和远交衰退。在四个种群中的三个种群中，花粉添加增强了结实率和每朵花的种子数量，表明存在花粉限制。在最小但最密集的种群中，花粉限制的程度最低。我们的结果表明，与“新稀有种”植物类似，“老稀有种”也可能面临近交衰退和花粉限制的风险。
