Japanese Stiltgrass (Microstegium vimineum) is the most invasive grass in the southeast US. Shade tolerance and rapid nutrient acquisition are believed to be central to its invasibility. However, the underlying mechanisms that facilitate M. vimineum nutrient acquisition are unclear. We conducted two experiments in growth chambers to examine whether M. vimineum form symbiotic associations with mycorrhizal fungi and thus confer a competitive advantage for nutrients. M. vimineum was grown (1) in pre-invaded field soil and sterilized pre-invaded field soil to determine the plant-soil feedback and (2) in the sterilized soil with a mixture of AMF inocula to determine the AM effect. Two additional treatments of N addition and AMF inoculum addition to pre-invaded field soils were used to examine nutrient release effects from soil sterilization and baseline mycorrhizal activity in the field soil, respectively.
Results/Conclusions
M. vimineum was found to be highly mycorrhizal with infection rates of 38-71%. Compared to growth in the field soil (control), M. vimineum biomass increased 4.4-fold in sterilized soil and 5.4-fold in sterilized soil with mycorrhizae after 12 weeks of growth. Morphological differences were also observed. With added AMF inoculum, the presence of branches and aerial roots increased 1.5 and 4.7-fold for plants grown in the field soil and 1.4 and 6.7-fold for plants grown in the sterilized soil. Mycorrhizal stimulation of branch and aerial root formation may serve as another mechanism by which M. vimineum can quickly take over new territory. Future studies will contribute to our understanding of invasive plant-microbial interactions and inform management strategies.
