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1. Elevated Temperature May Affect Nectar Microbes, Nectar Sugars, and Bumble Bee Foraging Preference

   https://doi.org/10.1007/s00248-021-01881-x  

   Russell, Kaleigh A.; McFrederick, Quinn S. (October 2021, Microbial Ecology)

   Abstract Floral nectar, an important resource for pollinators, is inhabited by microbes such as yeasts and bacteria, which have been shown to influence pollinator preference. Dynamic and complex plant-pollinator-microbe interactions are likely to be affected by a rapidly changing climate, as each player has their own optimal growth temperatures and phenological responses to environmental triggers, such as temperature. To understand how warming due to climate change is influencing nectar microbial communities, we incubated a natural nectar microbial community at different temperatures and assessed the subsequent nectar chemistry and preference of the common eastern bumble bee, Bombus impatiens . The microbial community in floral nectar is often species-poor, and the cultured Brassica rapa nectar community was dominated by the bacterium Fructobacillus . Temperature increased the abundance of bacteria in the warmer treatment. Bumble bees preferred nectar inoculated with microbes, but only at the lower, ambient temperature. Warming therefore induced an increase in bacterial abundance which altered nectar sugars and led to significant differences in pollinator preference. 

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2. Nectar compounds impact bacterial and fungal growth and shift community dynamics in a nectar analog

   https://doi.org/10.1111/1758-2229.13139  

   Mueller, Tobias_G; Francis, Jacob_S; Vannette, Rachel_L (February 2023, Environmental Microbiology Reports)

   Abstract Floral nectar is frequently colonised by microbes. However, nectar microbial communities are typically species‐poor and dominated by few cosmopolitan genera. One hypothesis is that nectar constituents may act as environmental filters. We tested how five non‐sugar nectar compounds as well as elevated sugar impacted the growth of 12 fungal and bacterial species isolated from nectar, pollinators, and the environment. We hypothesised that nectar isolated microbes would have the least growth suppression. Additionally, to test if nectar compounds could affect the outcome of competition between microbes, we grew a subset of microbes in co‐culture across a subset of treatments. We found that some compounds such as H₂O₂suppressed microbial growth across many but not all microbes tested. Other compounds were more specialised in the microbes they impacted. As hypothesised, the nectar specialist yeastMetschnikowia reukaufiiwas unaffected by most nectar compounds assayed. However, many non‐nectar specialist microbes remained unaffected by nectar compounds thought to reduce microbial growth. Our results show that nectar chemistry can influence microbial communities but that microbe‐specific responses to nectar compounds are common. Nectar chemistry also affected the outcome of species interactions among microbial taxa, suggesting that non‐sugar compounds can affect microbial community assembly in flowers. 

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3. Nectar metabolomes contribute to pollination syndromes

   https://doi.org/10.1111/nph.70217  

   MacNeill, Fiona T; Hunter, Sarah G; Muth, Felicity; Sedio, Brian E (July 2025, New Phytologist)

   ‘Pollination syndromes’, where convergent floral signals reflect selection from a functional pollinator group, are often characterized by physical features, yet floral rewards such as nectar may also reflect selection from pollinators. We asked whether nectar chemistry shows evidence of convergence across functional pollinator groups, i.e. a ‘chemical pollination syndrome’. We used untargeted metabolomics to compare nectar and leaf chemical profiles across 19 bee‐ and bird‐syndrome species, focusing on Salvia spp. (Lamiaceae), selected to maximize switching events between pollination syndromes.We found that independently derived bird‐syndrome nectar showed convergence on nectar traits distinct from bee‐syndrome nectar, primarily driven by the composition and concentration of alkaloid profiles. We did not find evidence for ‘passive leaking’ of nectar compounds from leaves since metabolite abundances were uncorrelated across tissues and many nectar metabolites were not present in leaves. Nectar and leaf metabolomes were strongly decoupled from phylogenetic relationships within Salvia. These results suggest that functional pollinator groups may drive the evolution of floral reward chemistry, consistent with our ‘chemical pollination syndrome’ hypothesis and indicative of selection by pollinators, but we also consider alternative explanations. In addition, our results support the notion that nectar chemistry can be decoupled from that of other tissues. 

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4. Review: Nectar biology: From molecules to ecosystems

   https://doi.org/10.1016/j.plantsci.2017.04.012  

   Roy, Rahul; Schmitt, Anthony J.; Thomas, Jason B.; Carter, Clay J. (September 2017, Plant Science)
5. On the horizon for nectar‐related research

   https://doi.org/10.1002/ajb2.1767  

   Liao, Irene T.; Hileman, Lena C.; Roy, Rahul (December 2021, American Journal of Botany)