Prediction of Plant Invasiveness

The black locust tree (Robinia pseudacacia) is widely used for erosion protection, as food source for bees, and timber. However, in climatically favourable regions it developed into an invasive species threatening native plant communities. Only a few of the many invasive plant species are trees, but their impact on natural ecosystems may be significant in terms of biomass and net primary production and they dominate vegetation successions longer than herbaceous species. The coordination of basic research interests with those of stakeholders in nature conservation requests the development of evaluation procedures aiming to determine the invasive potential of plant species. Case studies on known invasive plants represent an avenue to develop these procedures, and the black locust is well suited for such a task as it is known to for symbiotic relationships with nitrogen fixating soil bacteria and to possess the ability of clonal reproduction; both traits that are regarded to contribute as major factors to its invasiveness. But, a complex set of further factors determines the invasiveness of a plant species, among of which secondary metabolites may also play an important role; the "novel weapons" hypothesis considers secondary metabolites with toxic, in particular phytotoxic activities. The validity of this hypothesis is to be tested on various invasive plant species. Prerequisite for such a task is a thorough inventory of secondary metabolites with toxic, in particular phytotoxic activities in roots as well as in leaf litter. The assessment of putative effects as novel weapons on co-occurring native plant species requires the accomplishment of following tasks: (1) assessment of qualitative and quantitative composition in the plant organ; (2) decomposition and microbial conversion in soil; and (3) assessment of toxic properties of the identified compounds against other plants, microbes, and invertebrates in standardized bioassays.