Microbial impacts on plant fitness through their effects on floral scent and pollinator attraction

Background/Question/Methods Floral scents play very relevant roles in pollinator attraction. They are generated by the emission of volatile organic compounds (VOC) from flower tissues. Flower bacterial communities can affect floral VOC emissions by emitting their own VOCs, by affecting flower physiology and emission of floral VOCs, and by metabolizing the VOCs emitted by the flower. Such changes can have unknown impacts on pollinator attraction to flowers and also on pollinating efficiency and plant fitness. For this reason, we designed experiments to measure the effects of bacterial microbiota on floral scents and on pollinator attraction to flowers. The floral VOC emissions and contents of sterile and non-sterile elderberry (Sambucus nigra) and rapeseed (Brassica napus) plants were measured using GC-MS and later compared. Additionally, sterile and non-sterile rapeseed plants were left for one day in a natural plant community and the visits conducted by pollinators were recorded. The frequency of visits and the identity of the pollinators were noted to assess differences in pollinators’ visitation rates and composition. Finally, fruit and seed production were measured as estimates of plant fitness to assess the impact of bacteria on plant reproductive success.

Results/Conclusions Floral VOC emissions were lower in elderberry plants that were fumigated with antibiotics to eliminate epiphyte bacterial communities, compared to control plants that were fumigated with only an innocuous solvent. Flower VOC contents as well as respiration rates did not change, indicating an absence of damage to floral tissues. The removal of flower bacteria also changed the composition and proportion of VOCs in the blend: common terpenes such as β-ocimene, linalool, epoxylinalool and linalool oxide disappeared from floral scent one week after fumigation with antibiotics. These results show a key role of floral phyllospheric bacteria in the quantity and quality of floral VOC emissions which might have significant impacts on pollinator attraction and plant fitness.