Climate manipulation alters the role of pollinators in floral microbiome assembly of two subalpine wildflowers

Microbiomes are important mediators of stress, and climate change presents several key avenues that may disrupt host/microbiome interactions. In plants, floral microbiomes may be especially critical because of their potential to impact plant reproduction. Shifts in floral phenology are well-documented consequences of climate change that may expose flowers to different microbial species pools, abiotic stressors, and key biotic interactions. For example, pollinators play an important role in microbial dispersal, and disruption of plant-pollinator interactions can result in unique trajectories of floral microbiome assembly. In this study, we asked what the role of pollinators was in dispersing microbes to flowers under four different climate treatments. In 2024, snowmelt timing and air temperature were manipulated in a subalpine Rocky Mountain meadow (Rich Co., UT) to assess the effects of climate on floral phenology and microbiome assembly, focusing on two native wildflower species: Claytonia lanceolata (Montiaceae) and Delphinium nuttallianum (Ranunculaceae). Simultaneously, a pollinator limitation treatment was applied to assess the role of plant-pollinator interactions on floral microbiome assembly processes. Bacteria and fungi were cultured from individual flowers to assess microbial abundance. Phenology advanced for both plant species under climate manipulation. For bacteria in Claytonia and both bacteria and fungi in Delphinium, pollinator limitation reduced microbial abundance when climate was unmanipulated. However, this effect was weakened or reversed under nearly all altered climate treatments. This suggests that climate change may alter the roles of pollinators as microbial vectors between flowers, with potentially important ramifications for the assembly of floral microbiomes.