Meindl George A, Ashman Tia-Lynn
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA.
Am J Bot. 2015 Mar;102(3):379-89. doi: 10.3732/ajb.1400468. Epub 2015 Feb 25.
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For plant species that occur in heavy-metal-rich soil, floral metal accumulation may produce an "elemental filter" that reduces pollinator visitation rate and species richness and changes pollinator species composition relative to closely related species growing on normal soils. Consequently, metal hyperaccumulation may contribute to pollinator-mediated reproductive isolation between closely related plant species that differ in metal accumulation.•
To test these ideas, we characterized plant-pollinator interactions in a sympatric pair of species that differ in metal accumulation (Streptanthus polygaloides, a nickel (Ni) hyperaccumulator, and S. tortuosus, a nonaccumulator). To test the elemental filter hypothesis, we presented arrays of S. polygaloides that were grown in either Ni-treated or control soils to insects at both S. polygaloides and S. tortuosus sites and recorded visitation.•
Naturally occurring S. polygaloides hyperaccumulated Ni in anthers and accumulated Ni in nectar, while S. tortuosus did not. Floral visitation rates in natural populations were higher to S. tortuosus than S. polygaloides. In addition, while floral visitor richness was similar, few pollinator taxa were shared between the two plant species. Nickel-treatment of S. polygaloides reduced visits by bees, but only for arrays presented at S. tortuosus sites.•
We show that the Ni hyperaccumulator S. polygaloides hosts a distinct floral visitor community, indicating that metal accumulation creates a filter for pollinators, similar to that documented for herbivores. Our study highlights a novel mechanism by which the abiotic environment can alter plant-pollinator interactions, and consequently plant reproduction and speciation.
• 研究前提：对于生长在富含重金属土壤中的植物物种，花朵中的金属积累可能会产生一种“元素过滤器”，相对于生长在正常土壤中的近缘物种，它会降低传粉者的访花率和物种丰富度，并改变传粉者的物种组成。因此，金属超积累可能导致在金属积累方面存在差异的近缘植物物种之间由传粉者介导的生殖隔离。
• 方法：为了验证这些想法，我们对一对同域分布且在金属积累上存在差异的物种（多花链荚豆，一种镍超积累植物，和曲折链荚豆，一种非积累植物）之间的植物 - 传粉者相互作用进行了表征。为了验证元素过滤器假说，我们将在镍处理土壤或对照土壤中生长的多花链荚豆植株呈现给多花链荚豆和曲折链荚豆生长地的昆虫，并记录访花情况。
• 主要结果：自然生长的多花链荚豆在花药中超积累镍且花蜜中积累镍，而曲折链荚豆则没有。自然种群中曲折链荚豆的花朵访花率高于多花链荚豆。此外，虽然花朵访客的丰富度相似，但这两种植物物种之间很少有传粉者类群是相同的。对多花链荚豆进行镍处理减少了蜜蜂的访花，但仅针对在曲折链荚豆生长地呈现的植株。
• 结论：我们表明镍超积累植物多花链荚豆拥有一个独特的花朵访客群落，这表明金属积累为传粉者创造了一个过滤器，类似于食草动物的情况。我们的研究突出了一种非生物环境能够改变植物 - 传粉者相互作用，进而改变植物繁殖和物种形成的新机制。
