Plant-pollinator interactions and floral and nectar traits shape the diversity of the nectar mycobiome.

Beyond its essential role in plant–pollinator interactions, floral nectar serves as habitats for diverse fungal communities that can influence plant–animal mutualism. Although it has long been known that fungi can reach high densities in floral nectar, the factors structuring their diversity remain poorly understood. In this study, we evaluated how the presence of mycobiome influences nectar properties and how floral traits, nectar chemistry, and flower visitors’ presence shape nectar-inhabiting fungi diversity. We examined ten insect-pollinated plant species from nine families, encompassing a broad range of floral morphologies and flower visitor interactions. We recorded differences in sugar and amino acids presence in flowers with open and restricted visitors access. These differences are likely linked to the presence and activity of mycobiome introduced primarily through animal visits. Our results indicate that fungal diversity in nectar is associated with the presence of specific sugars, particularly fructose and glucose. In contrast, we found no significant relationships between fungal diversity and amino acid composition, floral traits, or flower visitor group. The generally weak effect of flower visitors on fungal diversity may be partially explained by a dilution effect in highly diverse floral environments, where microbial inoculation is distributed across many plant hosts.