Attract and repel
We know for a long time that flowers attract pollinators with scent. But about the effect of the composition of those scents researchers know relatively little. Do plants with a more divers scent bouquet also attract more pollinators? And what about its effect on bacteria? That were the main questions of the authors of the article “Floral scent chemodiversity is associated with high floral visitor but low bacterial richness on flowers”.
To find an answer the researchers headed to the alpine meadows. There the researchers observed for days at and end 39 species of flowering plants. Keeping score of which pollinators visited which flowers. The researchers also took scent and flower samples. The first to find out the exact composition of the scent bouquet. The second to find out which bacteria could be found on the flowers.
Back in the lab, after analysis of the scent and bacteria samples, the researchers combined these with the numbers of how many and which pollinators visited each plant species. They found that plants that attracted more species of pollinators has a more divers scent bouquet. But for the bacteria present on the flowers the opposite was found. A more divers scent bouquet resulted in less bacterial species on the flower.
Double function of scent molecules
For the researchers this appeared to be at first glance a strange contradiction. That is because bacteria often research the flowers via an intermediate, often a pollinator. Now has each bacteria its own preferences, which is shown by that bacteria species at different pollinators are different. Together you would expect that with a more divers pollinator population visiting the flower, they would leave behind a more divers bacterial population on the flowers, than when only a single pollinator species visits the flower. But the researchers observed the opposite.
An explanation can lay in the second function of scent molecules. These are not only attracting pollinators but are also inhibiting bacterial growth. Not of all bacteria, but from a select group. Plants with lots of different scent molecules can in this way inhibit the growth of different groups of bacteria.
For now, this is still a hypothesis, one that still needs to be tested. But it is an interesting one. Because if correct, it means that plants not only actively shape their microbiome at their roots but also those of their flowers.
Literature
Hanusch, M., Dötterl, S., Larue-Kontić, A.-A.C., Keller, A. and Junker, R.R. (2025), Floral scent chemodiversity is associated with high floral visitor but low bacterial richness on flowers. New Phytol. https://doi.org/10.1111/nph.70600
Plant en Zo 