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Experimental fertilization increases amino acid content in floral nectar, fruit set and degree of selfing in the orchid Gymnadenia conopsea

  • Plant-microbe-animal interactions - Original research
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Abstract

Floral traits have evolved to maximize reproductive success by attracting pollinators and facilitating pollination. Highly attractive floral traits may, however, also increase the degree of self-pollination, which could become detrimental for plant fitness through inbreeding depression. Floral nectar is a trait that is known to strongly mediate pollinator attraction and plant reproductive success, but the particular role of the nectar amino acid (AA) composition is poorly understood. Therefore, we experimentally manipulated the nectar AA composition and abundance of the Lepidoptera-pollinated orchid Gymnadenia conopsea through soil fertilization, and we quantified AA content and AA composition through high performance anion exchange chromatography with pulsed amperometric detection. Mixed models were then used to evaluate differences in pollinia removal, fruit set, seed set and degree of selfing between fertilized and control individuals. Selfing rates were estimated using microsatellite markers. We found that fertilized individuals had a significantly higher nectar AA content and an altered AA composition, whereas plant height, number of flowers, nectar volume and sugar concentration remained unchanged. Fertilized individuals also had significantly more pollinia removed and a higher fruit set, whereas control plants that did not receive the fertilization treatment had significantly fewer selfed seeds, and more viable seeds. Although we cannot exclude a role of changes in floral scent following the fertilization treatment, our results strongly suggest a relation among nectar AA composition, fruiting success and selfing rates. Our results also indicate potential consequences of nutrient pollution for plant reproductive success, through the induced changes in nectar AA composition.

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Acknowledgments

P. G. and T. C. were funded by the Research Foundation Flanders. This project was financed through a KU Leuven BOF-OT grant. The authors thank Gert Verheyen, Timmy Reijnders and Rudy Vergauwen who assisted with field and lab work and high performance anion exchange chromatography with pulsed amperometric detection analysis. We thank the anonymous reviewers and handling editor M. Kant for detailed comments that greatly improved the manuscript.

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Authors and Affiliations

  1. Plant Conservation and Population Biology, Biology Department, KU Leuven, Heverlee, Belgium

    Pieter Gijbels, Tobias Ceulemans & Olivier Honnay

  2. Laboratory of Molecular Plant Biology, Biology Department, KU Leuven, Heverlee, Belgium

    Wim Van den Ende

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  1. Pieter Gijbels
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  2. Tobias Ceulemans
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Correspondence to Pieter Gijbels.

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Communicated by Merijn Kant.

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Gijbels, P., Ceulemans, T., Van den Ende, W. et al. Experimental fertilization increases amino acid content in floral nectar, fruit set and degree of selfing in the orchid Gymnadenia conopsea . Oecologia 179, 785–795 (2015). https://doi.org/10.1007/s00442-015-3381-8

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