Format: ORAL

Geerts, S.1, Le Roux, J.J.2

1 Department of Conservation and Marine Sciences, Cape Peninsula University of Technology, PO Box 652, Cape Town, South Africa, 8000 2 Department of Biological Sciences, Macquarie University, Sydney, New South Wales, Australia, 2109

Mutualisms are thought to be important in the invasion dynamics of alien plant species. There is no guarantee that plants will encounter suitable mutualistic partners in a novel environment. When a mutualistic partner is co-introduced, or is a generalist and easily co-opts mutualists, invasion is more probable. If plants are more specialized in their mutualistic requirements or require multiple mutualistic partners, invasion might be curbed. Most studies consider only one type of mutualistic relationship, but many plant species typically interact with multiple types of mutualists. Therefore in this study we explore the interactions between two non-native legumes (Genista monspessulanaandSpartium junceum) and their associated below-ground (nitrogen-fixing rhizobia) and above-ground (pollinators) mutualists. We conducted pollinator observations, breeding system experiments and collected root nodules for 16S rRNA gene amplification. BothG. monspessulanaandS. junceumare dependent on pollinators for seed production but are successfully pollinated in South Africa.Genista monspessulanais pollinatedlargely by honeybees and carpenter bees whilst the bigger flowers offS. junceumare only pollinated by carpenter bees. Differences in rhizobium associations (nodulation) were much more pronounced. We foundG. monspessulanapopulations to be nodulated by at least four distinct lineages ofBradyrhizobium, while forS. junceumthis was much less. The wider distribution ofS. junceumcompared toG. monspessulanalikely reflects the differences in propagule pressure (S. junceumwas a popular garden plant). The inability to nodulate, and relative low rates of pollination ofS. junceum, suggest it currently poses a much lower risk thanG. monspessulanain becoming a widespread invasive species in South Africa.