Pollinator visitation on Na-enriched plants in a subalpine meadow

Many plants have evolved nutrient rewards to attract pollinators to flowers, but most research has focused on the sugar content of floral nectar resources. Concentrations of sodium in floral nectar (a micronutrient in low concentrations in nectar) can vary substantially both among and within co-occurring species. Sodium concentrations in floral nectar might play an important and underappreciated role in plant-pollinator interactions, especially because many animals, including pollinators, are sodium-limited in nature. Yet, the consequences of variation in sodium concentrations in floral nectar have gone largely unexplored. Here, we investigate whether enriching floral nectar with sodium influences the composition, diversity, and abundance of pollinator interactions. We experimentally enriched sodium concentrations in four plant species in a subalpine meadow in Colorado, USA. We found that flowers with sodium-enriched nectar received more visits from a greater diversity of pollinator vis..., Experimental design. We selected four focal species for this experiment: Delphinium barbeyi (Ranunculaceae), Erigeron speciosus (Asteraceae), Helianthella quinquenervis (Asteraceae), and Heliomeris multiflora (Asteraceae). These plant species have varied floral morphologies and have an abundant and diverse community of floral visitors (CaraDonna and Waser 2020; Bain et al. 2022). All focal plant species co-occur in this subalpine meadow, are abundant, and co-flower (in July). For each species, we selected 5 paired plants; pairs were typically within 1 meter of one another, similarly sized, and had a similar number of flowers. We labeled D. barbeyi and E. speciosus individuals but considered adjacent groupings (2-5 individuals) of H. quinquenervis and H. multiflora a “single plant” because each individual has few or one inflorescence. For each pair, one plant received the sodium-enriched nectar treatment and the other received the control treatment. Control nectar contained 50% sucrose (..., , # Pollinator visitation on Na-enriched plants in a subalpine meadow

[https://doi.org/10.5061/dryad.7h44j1018](https://doi.org/10.5061/dryad.7h44j1018)

#### Contributors:

Ethan VanValkenburg (contact): [e-mail]
Nathan J Sanders
Paul CaraDonna

Here, we investigate whether enriching floral nectar with sodium influences the composition, diversity, and abundance of pollinator interactions. We experimentally enriched sodium concentrations in four plant species in a subalpine meadow in Colorado, USA. We found that flowers with sodium-enriched nectar received more visits from a greater diversity of pollinator visitors throughout the season. Each pollinator species foraged more frequently on flowers enriched with sodium and showed evidence of other changes to pollinator foraging behavior, including greater dietary evenness. These findings are consistent with the ‘salty nectar hypothesis,’ providing evidence for the importance of sodium limitation in pollinators and suggesting th...