植物花序中的资源配置通常在花发育的时间或者位置上存在差异。植物的化学性状在自身生长发育以及植物与环境的相互作用中发挥重要作用, 但是化学性状是否存在花序内的差异, 目前还不清楚。为了解花序中不同位置上花报酬(花粉和花蜜)化学性状的差异, 本文以总状花序的中甸乌头(Aconitum piepunense)为研究对象, 从下往上, 将花序中不同位置的花分为基部花、中部花和顶部花, 观察传粉者在花序中的访问特点, 测量不同位置花的花蜜体积和糖浓度, 分别检测分析不同位置花的花粉和花蜜的化学物质的种类和相对含量。结果表明: 中甸乌头的传粉者弗里熊蜂(Bombus friseanus)和圣熊蜂(B. religiosus)通常由基部到顶部进行访花, 对不同位置花的单花访问时间和访花频率不存在显著性差异。基部花的花蜜体积高于中部花、顶部花, 3个位置的花蜜糖浓度不存在显著差异。花粉和花蜜中次级代谢物的相对含量和种类数都显著高于初级代谢物的相对含量和种类, 花粉中初级代谢物和次级代谢物的相对含量和种类数都显著高于花蜜。花粉和花蜜中的绝大部分的化学物质的相对含量和种类数在花序中的3个位置整体上不存在显著性差异。研究表明熊蜂为主要传粉者的中甸乌头, 其总状花序内上、中、下3个位置花的花粉和花蜜的化学性状不存在明显的结构效应。

Aims: Floral resource allocation often varies across developmental time and across locations in inflorescences. The chemical profile of a plant plays an important role in its growth, development, and interaction with its environment; however, it remains unclear whether such chemical traits vary among floral positions in a single plant. We aim to investigate the variation in chemical profiles of floral reward (pollen and nectar) at different positions of a single plant’s inflorescences.

Methods: Flowers in racemes of Aconitum piepunense (aconite) were categorized into three positions (basal, middle and distal). In each of the three positions, we observed pollinator foraging behaviors and measured nectar volume and sugar concentration. We then measured and analyzed the types and relative contents of chemical compounds within the pollen and nectar of flowers at each of the three positions.

Results: The two major pollinators (Bombus friseanus and B. religiosus) typically visited flowers from basal to distal in a sequential order in A. piepunense. Neither the bumblebee visit frequency nor the duration per flower significantly differed among the three positions. Flowers at the bottom of each position secreted more nectar by volume than the middle and upper flowers, but this volume was not significantly different in terms of the nectar sugar concentration across positions. We also found that the relative contents and types of secondary metabolites within the pollen and nectar were both significantly higher than those of primary metabolites. Further, the relative contents and classes of secondary metabolites were significantly higher in pollen than in nectar. Finally, we observed that the relative content and classes of most chemical profiles within pollen or nectar did not significantly differ at basal, middle, or distal flower positions.

Conclusion: Our results indicate that in the raceme of bumblebee-pollinated A. piepunense, floral positioning within a single plant has no clear impact on the chemical profiles of its pollen and nectar.