Nectar sugars and amino acids in day- and night-flowering Nicotiana species are more strongly shaped by pollinators’ preferences than organic acids and inorganic ions

Abstract

Floral nectar contains mainly sugars but also amino acids, organic acids, inorganic ions and secondary compounds to attract pollinators. The genus Nicotiana exhibits great diversity among species in floral morphology, flowering time, nectar compositions, and predominant pollinators. We studied nectar samples of 20 Nicotiana species, composed equally of day- and night-flowering plants and attracting different groups of pollinators (e.g. hummingbirds, moths or bats) to investigate whether sugars, amino acids, organic acids and inorganic ions are influenced by pollinator preferences. Glucose, fructose and sucrose were the only sugars found in the nectar of all examined species. Sugar concentration of the nectar of day-flowering species was 20% higher and amino acid concentration was 2-3-fold higher compared to the nectar of night-flowering species. The sucrose-to-hexose ratio was significantly higher in night-flowering species and the relative share of sucrose based on the total sugar correlated with the flower tube length in the nocturnal species. Flowers of different tobacco species contained varying volumes of nectar which led to about 150-fold higher amounts of total sugar per flower in bat- or sunbird-pollinated species than in bee-pollinated or autogamous species. This difference was even higher for total amino acids per flower (up to 1000-fold). As a consequence, some Nicotiana species invest large amounts of organic nitrogen for certain pollinators. Higher concentrations of inorganic ions, predominantly anions, were found in nectar of night-flowering species. Therefore, higher anion concentrations were also associated with pollinator types active at night. Malate, the main organic acid, was present in all nectar samples but the concentration was not correlated with pollinator type. In conclusion, statistical analyses revealed that pollinator types have a stronger effect on nectar composition than phylogenetic relations. In this context, nectar sugars and amino acids are more strongly correlated with the preferences of predominant pollinators than organic acids and inorganic ions.

Sugar, amino acid and inorganic ion profiling of the honeydew from different hemipteran species feeding on Abies alba and Picea abies

“…It could be assumed that this difference is caused by different ratios of sugars-to-inorganic ions in honeydew and floral nectar, assuming that they are lower in nectar. However, the sugar-to-cation and the sugar-to-anion ratios ( Table 4) were similar or even higher in honeydew than in floral nectar of other plant species [38,55]. Therefore, differences in the content of inorganic ions in both types of honey must have further and other reasons.…”

From plant fungi to bee parasites: mycorrhizae and soil nutrients shape floral chemistry and bee pathogens

“…The control diet contained a wildflower pollen blend collected by honey bees from an organic farm in North Dakota, USA and artificial sugar water mimicking the 12:15:10 glucose : fructose : sucrose ratios in N. tabacum nectar (Tiedge and Lohaus 2017) and the 16% overall sugar concentration observed in our nectar. To assess the effect of diet from plants grown under different soil conditions on Crithidia-infected B. impatiens (BioBest, Leamington, Ontario, Canada), infected bees were provided with pollen and nectar from one of the four treatment combinations, or a control diet.…”

Nectar composition in moth-pollinated Platanthera bifolia and P. chlorantha and its importance for reproductive success

“…One of these traits being the evolutionary answer for pollinators' preferences is nectar. Many studies document that nectar concentration and composition are often linked with pollinator types (Baker and Baker 1983;Nicolson and Thornburg 2007;Petanidou 2007;Witt et al 2013;Fowler et al 2016;Tiedge and Lohaus 2017). Pollinators have different requirements with respect to nectar content, both for sugar and amino acid (AA) concentrations, composition and other nectar components such as nectarins, vitamins, phenolics, alkaloids, terpenoids, lipids, metal ions and phytohormones (Baker and Baker 1983;Adler 2000;Petanidou 2007;Gijbels et al 2014Gijbels et al , 2015aRoy et al 2017;Tiedge and Lohaus 2017).…”