Does an invader have a bright side? Floral reward in two Solidago species.
The knowledge of nectar secretion and pollen production is important for understanding the biology of invasive species. In the present paper, the floral reward in Solidago canadensis and S. gigantea (Asteraceae), two invasive plant species in Europe, were investigated. Flowers of Solidago species are protandrous. The floral nectar was found to be rich in hexose (sucrose/fructose/glucose - 13.8/32.7/53.5% in S. canadensis and 18.3/35.1/46.6% in S. gigantea). The per-flower rewards (sugars/pollen) in the Solidago species were not abundant; however, due to the formation of dense populations and massive floral display, high amounts of resources were produced at the community level. The mean sugar output was 482.3 kg/ha in S. canadensis and 121.6 kg/ha in S. gigantea. The mean pollen yield was 30.7 kg/ha (S. canadensis) and 6.5 kg/ha (S. gigantea). In the landscape with limited floral resources, the nectar and pollen available in Solidago flowers are important and can provide additional (or even exclusive) food resources for pollinators during summer/late summer. In particular, areas invaded by Solidago species may be attractive to beekeepers, as >80.0% of visits were performed by Apis mellifera. However, a broad spectrum of wild insect visitors (including Bombus spp., Vespula spp., Diptera, Lepidoptera, Coleoptera) deserves further studies to assess the impact of mass flowering in Solidago species on the native plant species-insect interactions.