Wagner Johanna, Lechleitner Martin, Hosp Daniela
Institute of Botany, Faculty of Biology, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria
Institute of Botany, Faculty of Biology, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria.
Am J Bot. 2016 Mar;103(3):375-87. doi: 10.3732/ajb.1500214. Epub 2016 Mar 1.
Seed output of high-mountain plants in the uppermost life zones is highly variable. One possible reason might be pollen limitation due to inadequate pollinator services.
We tested this hypothesis for the insect-pollinated species Cerastium uniflorum, Ranunculus glacialis, and Saxifraga bryoides, which have their distribution center in the subnival and nival zone of the European Central Alps. We recorded insect visitors and determined their impact as pollinators. By analyzing pollination success and seed set following natural and saturating hand pollination, the magnitude of quantitative and qualitative pollen limitation was assessed.
Anthomyiid and muscid flies had the highest pollination impact for R. glacialis and S. bryoides and syrphids for C. uniflorum. Natural stigma pollen load was highly variable in individual flowers of all species, but in most cases the number of conspecific pollen grains clearly exceeded the number of ovules to be fertilized. There was also a surplus in germinated pollen grains, whereas the pollen tube to ovule ratio was only sufficient in R. glacialis (2.6 on average) and S. bryoides (1.3), but not in C. uniflorum (0.6). Accordingly, seed to ovule ratio was around 0.8 in R. glacialis, 0.7 in S. bryoides but 0.4 in C. uniflorum. In C. uniflorum, saturating pollination slightly increased seed set. Regression analyses revealed that natural pollination success was more frequently limited by quality than by quantity.
Our results do not support the idea of chronic, widespread pollen limitation in the subnival but rather fit into the concept of parental optimism by overinvesting in the number of ovules as an adaptation to variable resource availability.
高山植物在最高生命地带的种子产量变化很大。一个可能的原因可能是传粉者服务不足导致的花粉限制。
我们对昆虫传粉的单花卷耳、冰川毛茛和苔藓虎耳草这几种植物验证了这一假设，它们的分布中心位于欧洲中部阿尔卑斯山的亚冰雪带和冰雪带。我们记录了访花昆虫，并确定它们作为传粉者的影响。通过分析自然授粉和饱和人工授粉后的授粉成功率和结实率，评估了定量和定性花粉限制的程度。
花蝇科和蝇科的苍蝇对冰川毛茛和苔藓虎耳草的授粉影响最大，而食蚜蝇对单花卷耳的授粉影响最大。所有物种的单朵花中，天然柱头花粉负载量变化很大，但在大多数情况下，同种花粉粒的数量明显超过了待受精胚珠的数量。萌发的花粉粒也有剩余，而花粉管与胚珠的比例仅在冰川毛茛（平均为2.6）和苔藓虎耳草（1.3）中足够，但在单花卷耳中不足（0.6）。因此，冰川毛茛的种子与胚珠比例约为0.8，苔藓虎耳草为0.7，而单花卷耳为0.4。在单花卷耳中，饱和授粉略微提高了结实率。回归分析表明，自然授粉成功率更常受到质量而非数量的限制。
我们的结果不支持亚冰雪带长期存在广泛花粉限制的观点，而是符合亲本乐观主义的概念，即通过过度投资胚珠数量来适应资源可用性的变化。
