Floral scent chemodiversity is associated with high floral visitor but low bacterial richness on flowers.

Floral scents are complex blends of volatile compounds, yet the influence of floral scent chemodiversity, the richness, evenness, and functional disparity of phytochemical compounds in shaping interactions with flower visitors and microbes remains largely unexplored. Using a dataset of alpine plant species, we investigated how floral scent chemodiversity affects flower visitor and bacterial diversities on flowers. Our results reveal that high floral scent chemodiversity is associated with increased flower visitor richness but reduced bacterial richness on flowers. These findings led us to propose the 'Filthy Pollinator Hypothesis'. Our hypothesis rests on two core ideas: flowers with chemodiverse scents attract a broader range of flower visitors, thereby increasing the potential for microbial transmission; and floral scent chemodiversity acts as a selective filter, mitigating the risks of unwanted microbial colonization by preventing the establishment of detrimental microbes while still allowing the establishment of a healthy microbiome. Floral scent chemodiversity may therefore not only shape the specialization/generalization of flower visitor assemblages but also act as a regulatory mechanism for microbial communities. By highlighting the multifunctionality of chemodiversity in structuring plant-animal and plant-microbe interactions, our study advances the understanding of chemodiversity and underscores its importance in plant ecology.