Nectar sugar composition and floral scent compounds of diurnal and nocturnal Conophytum species (Aizoaceae)

The putative correlation between nectar sugar composition, floral scent compounds, and the pollination syndrome (diurnal vs nocturnal) was evaluated in the genus Conophytum (Aizoaceae). Nectar sugar compositions of 39 species, subspecies, and varieties of the genus Conophytum were analysed via high performance liquid chromatography (HPLC). Nectar contained mainly glucose and fructose and in several cases small amounts of sucrose. In all Conophytum species investigated nectar is hexose-dominant, or at least hexose-rich. An interesting variation in the fructose: glucose ratio was observed - samples of diurnal species had significantly higher fructose: glucose ratios than samples of nocturnal species. Floral scents of 27 diurnal and nocturnal Conophytum species from 11 sections were collected by headspace adsorption and analysed via gas chromatography-mass spectrometry (GC-MS). In total 33 compounds could be identified by their mass spectra as well as by their relative retention times. Most of the species were dominated by only a few (3-5) floral scent compounds. The species showed basic similarities in being dominated by benzenoids accompanied by fatty-acid derivatives, nitrogen-containing compounds, and terpenoids. The floral scent composition of all species was dominated by benzaldehyde and benzeneacetaldehyde. Compared to nocturnal species, diurnal species are characterised by a lower number of compounds, low amounts of aromatic esters, and an almost total absence of nitrogen-containing compounds. It is assumed that the relatively high amounts of aromatic esters in the scent of some nocturnal species are an adaptation to moth pollination.