Microstegium vimineum (Japanese stilt-grass) is an invasive grass introduced to the U.S. in the early 20th century, which has since spread to 23 states.  It rapidly colonizes and dominates forests after a disturbance such as a timber harvest, road cut, or scouring flood.  Once M. vimineum has colonized a site, it forms a dense, monospecific stand, reducing plant diversity and inhibiting forest regeneration. Positive soil feedback has been suggested as a mechanism behind the dominance of invasive plants such as M. vimineum.  Previous studies have determined that M. vimineum alters the structure and function of the soil community; specifically, this species alters the soil pH, bacterial community structure, and enzyme activity.  However, no research had yet determined whether M. vimineum participates in a positive soil feedback, promoting a soil microbial community that facilitates greater relative growth or flowering in M. vimineum compared to the native plant community.  To investigate this mechanism, we conducted a full factorial experiment with three plant treatments (M. vimineum alone, M. vimineum with a native community, and the native community alone) and three soil inocula (live inoculum from an invaded site, live inoculum from a control site, and a sterile mixed inoculum).  The three inoculum treatments were added as liquids to a sterile sand/soil mixture in the greenhouse to control for soil nutrients, texture, and seed bank.  

Results/Conclusions
Our results show a negative soil feedback occurring under interspecific competition, with the native plants having a higher relative biomass in the invaded inoculum.  These results suggest that M. vimineum promotes a soil microbial community more beneficial to native plants than to itself, which has two implications: 1) M. vimineum’s ability to outcompete natives is not due to a positive soil feedback; and 2) the native community can be re-established on a restoration site without the use of soil inoculum.