No significant differences found in chemical traits of pollen and nectar located in different positions across Aconitum piepunense racemes
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.
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