Floral scent is considered an important long-distance signal that attracts pollinators, but also has been suggested to function at shorter distances such as within-flower nectar guides or as a defense against antagonists. Indeed, in some species floral scent production and emission show spatial patterns of variation within flowers, as certain compounds are exclusively emitted from specific floral tissues. In other species, the different volatile organic compounds that constitute the floral bouquet are emitted evenly from the entire flower. Here, we summarize the current evidence on floral scent variation within flowers by combining a literature review of published data on tissue-level floral scent variation (41 species) with floral scent dissections (17 species). For each species, we recorded the total number of volatile compounds separately and grouped in major chemical classes. To facilitate comparisons across diverse species, we compared volatiles emitted by 1) the whole flower, 2) the visual floral tissues (i.e. petals and colored structures), 3) non-visual floral tissues (i.e. green parts and reproductive structures), as well as 4) the compounds emitted by both visual and non-visual tissues. Results show that floral scent variation is frequent, but by no means ubiquitous, occurring in species from distantly related groups. We discuss the two main functional hypotheses promoting floral scent variation within flowers, i.e. as a pollinator attractant at short-distances or a defensive function against antagonists, together with non-functional hypotheses (e.g. pleiotropic effects, ecological costs). We point out further directions on this topic and suggest experimental approaches testing the attractiveness of compounds emitted by different floral parts alone and in combination with other floral signals. Our synthesis provides a foundation for future studies on the functional ecology of floral scent and reinforces the idea of high complexity in floral chemical signals.

中文翻译：

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花内气味散发的空间变化

花香被认为是吸引传粉者的重要长距离信号，但也有人建议在较短距离内发挥作用，例如花内花蜜引导或作为对抗拮抗剂的防御。事实上，在某些物种中，花香的产生和散发显示出花内变异的空间模式，因为某些化合物仅从特定的花组织中散发出来。在其他物种中，构成花香的不同挥发性有机化合物从整朵花中均匀散发。在这里，我们通过将已发表的组织级花香变异（41 种）数据的文献综述与花香解剖（17 种）相结合，总结了目前关于花内花香变异的证据。对于每个物种，我们分别记录了挥发性化合物的总数，并按主要化学类别分组。为了促进不同物种之间的比较，我们比较了 1) 整朵花、2) 视觉花组织（即花瓣和有色结构）、3）非视​​觉花组织（即绿色部分和生殖结构）以及4）视觉和非视觉组织发出的化合物。结果表明，花香的变化是频繁的，但绝不是普遍存在的，发生在远亲群体的物种中。我们讨论了促进花内花香变化的两个主要功能假设，即作为短距离传粉者引诱剂或对抗拮抗剂的防御功能，以及非功能假设（例如多效性效应、生态成本）。我们指出了关于这个主题的进一步方向，并提出了测试不同花卉部分单独释放的化合物以及与其他花卉信号结合的化合物的吸引力的实验方法。我们的合成为未来花香功能生态学的研究奠定了基础，并强化了花卉化学信号高度复杂性的想法。