Lespedeza cuneata, an invasive legume, is allelopatic against certain grass species, and it engages in a mutualistic relationship with Bradyrhizobium, a N-fixing bacteria. This mutualism likely improves the nutrient status of L. cuneata, and plants in restored tallgrass prairie sites with a row-crop agricultural history have higher rhizobia densities that could affect a plant's ability to produce allelochemicals. Accordingly, L. cuneata invasions are a good candidate to test the interaction between the novel weapons and mutualism facilitation hypotheses. We expected that soil from the L. cuneata rhizosphere from restored prairie sites would inhibit germination and seedling growth more than rhizosphere soil from native prairie sites. Soil samples were collected from inside L. cuneata rhizosphere and 1 m away from a L. cuneata at restored and native prairie sites. Soil extracts were used to germinate seed of 12 different species. Lycopersicum esculentum var. Rutgers VF seed was used to test for the potential allelopathic effects of the soil extracts. The remaining species tested were grasses and forbs native to tallgrass prairie, including two congeneric species. Seed germination rate and seedling size were measured to evaluate the strength of allelopathy in soils from each site.
Results/Conclusions
Soils from the rhizosphere of L. cuneata in restored prairie sites reduced germination rates of L. esculentum, Sorghastrum nutans, Lespedeza capitata, and Lespedeza virginica significantly more than soil from native prairies. Soils from the L. cuneata rhizosphere in restored prairie sites also reduced the seedling length of L. esculentum, Andropogon gerardii, L. capitata, and L. virginica. Lespedeza cuneata did not affected germination and seedling size of forbs except for congeneric legumes, nor was it self-inhibitory. Allelopathy was more pronounced in restored prairie sites, possibly resulting from a stronger interaction with rhizobia in restored prairies thereby providing simultaneous preliminary support for both the novel weapons and mutualism facilitation hypotheses.