Warming and Drought Stress Modify Scent and Rewards in Flowers of Highbush Blueberry Affecting Pollinator Preferences

Changes in environmental temperatures and water availability can disrupt plant-pollinator interactions by altering floral attractive and rewarding traits. Here, we investigated the effects of warming and drought on floral scent and rewards in Vaccinum corymbosum (an entomophilous crop), and how these changes affect pollinator behavior. Plants were exposed to two temperatures (24 °C and 28 °C) and two watering treatments (optimal watering, W+, and water stress, W-). We measured floral volatiles, pollen and nectar quantity, as well as the nutritional composition of pollen (C, carbon, and N, nitrogen percentage) and nectar (hexose-to-amino acids ratio). Bioassays with honeybees were conducted to assess responses to the attractive and rewarding traits specific to each treatment. Floral volatiles significantly increased at 28° W+; nevertheless, they declined under the combination of both warming and drought. Pollen and nectar production were only negatively affected by warming. Pollen's nutritional composition was negatively affected by the interaction of both stresses, with greater reductions in % C and N occurring when both stresses were combined. We observed that the synthetic floral scent representing the blend emitted by flowers under 28° W+ conditions, at low concentrations, attracted the highest percentage of honeybees. Additionally, honeybees tended to visit artificial diets of pollen with a more nutritious composition (50% carbon and 6% nitrogen), as found in 24° W+. We showed that changes in the composition of floral scent and pollen in varieties of V. corymbosum affected pollinator preferences in laboratory bioassays. This study contributes to our understanding of how climate change may impact trophic interactions by showing that changes in floral traits are associated with alterations in pollinator preferences.