Investigating the impacts of floral visitor identity on nectar volume, microbial density, and microbial diversity in four subalpine wildflower species

Nectar microbial communities in flowers can be vectored by rainwater, soil, and animal visitors. Previous studies have shown that primary nectar robbers, secondary nectar robbers, and pollinators bring different microbial communities to flowers, and these distinct microbial communities can differentially impact aspects of floral phenotype including nectar smell and taste. In sensitive wildflower populations dependent on threatened bumblebee populations, it is important to understand the complex interactions between flowers, microbes, and floral visitors. This study explores the differences in microbial abundance, microbial diversity, and nectar volume between flowers depending on floral visitor identity. We studied these questions in four subalpine flowering species in the Colorado Rocky Mountains: Delphinium nuttallianum, Mertensia ciliate, Corydalis caseana ssp. brandegeei, and Linaria vulgaris. We broadly found that that visitor identity impacted nectar volume and microbial diversity and abundance. Preventing pollinator visits resulted in lower microbial abundance and diversity. There were significant differences in microbial diversity and abundance between robber-visited and pollinator-visited flowers and significant differences in nectar volume between robbed and unrobbed flowers.