COS 219-4 - Mycorrhizal interactions and nutrient supply mediate floral trait variation and bee visitation

Background/Question/Methods

Floral traits, including floral display and nutritional rewards from pollen and nectar, drive bee visitation and are also critical for bee growth, development, and reproduction. However, floral traits can vary widely in quality and quantity across environmental contexts. Therefore, it is important to characterize the ecological mechanisms that can enhance floral resources to increase bee visitation and by extension support bee health. Recent focus has shifted belowground to examine the extent to which microorganisms in the soil can improve plant performance, including floral resource production. Using a controlled greenhouse and field experiment , we investigated how microbial community composition and nutrient availability. Specifically, we examined how functional differences among arbuscular mycorrhizal fungi (AMF) and phosphorus supply, affect floral resource production and how that, in turn, affects bee visitation.

Results/Conclusions

We found that AMF richness or functional diversity enhanced floral display (flower size and number) and rewards (nectar availability and pollen protein) and increased pollinator visitation (number and duration of visits) even phosphorus supply was low. Using structural equation modeling, we further demonstrate that AMF influenced bee foraging dynamics by increasing floral display; plants received a greater number of bee visits when flowers were larger. However, functional tradeoffs did emerge for plant host and AMF associations because reductions in flower size also tracked with greater root colonization suggesting that, in some cases, carbon transfer from plants to AMF may negatively impact flower growth. Overall, we find that the effect of AMF on floral traits and pollinator visitation was not homogenous; instead, functional differences among AMF, based on life-history strategies, interact with phosphorus supply resulting in varying effects on floral traits and, subsequently, bee foraging dynamics.