Abiotic conditions affect nectar properties and flower visitation in four herbaceous plant species

Both plant nectar production and insect activity are highly dependent on abiotic environmental conditions. Furthermore, the foraging behaviour of insect pollinators can be affected by nectar properties. In the context of climate change, it is important to understand how plant-pollinator interactions respond to temperature and other abiotic factors. We investigated the effect of natural variation in temperature and solar radiation on nectar quantity (nectar volume) and quality (sucrose concentration and sucrose mass) and on flower visitation rates in four herbaceous plant species (Dictamnus albus, Lamium album, Salvia officinalis, Vincetoxicum hirundinaria) in the Botanical Garden Halle (Germany). Temperature affected nectar properties in all four species. Solar radiation affected nectar quantity and quality in two species, most likely by affecting flower temperature. The number of flower visits was unimodally related to temperature for two species and positively related to solar radiation in another. The variable responses across plant species in the effects of abiotic factors on nectar properties and flower visitation patterns may be due to differences in flower shape and colour, to differences in the composition of flower visitors, or due to other unmeasured extrinsic factors that vary across patches where these species occur. Our study highlights the importance of considering direct and indirect effects of climate factors on pollinator visitation in multiple plant species.