Abiotic factors, not mycorrhizal associations, predict growth and abundance of the invasive grass Microstegium vimineum

Kimberly A. Koenig, Biology Department, University of Louisville, Louisville, KY and Sarah Emery, Biology Dept., University of Louisville, Louisville, KY

Background/Question/Methods
Invasive plants often form novel associations with soil organisms, and in some systems arbuscular mycorrhizal fungi (AMF) has been shown to facilitate establishment and spread of these plants. Microstegium vimineum, known as stiltgrass, is an invasive annual grass which creates dense beds in native forest areas, outcompetes native understory species, decreases diversity, and prevents the regeneration of native trees. Development of more successful management strategies for this species depends on understanding the factors contributing to its success. Microstegium is known to form associations with AMF, but research has yet to demonstrate whether this association has a role in Microstegium invasion and dominance over native vegetation. We conducted a field survey in invaded and uninvaded habitats across six sites near Louisville, KY to evaluate the role of AMF in Microstegium invasion relative to abiotic factors known to be important to success of this species (e.g., light, soil nutrients).
Results/Conclusions
We determined canopy cover to be the strongest predictor of Microstegium presence, followed by soil moisture. We found no difference in AMF extraradical hyphal abundance between invaded and uninvaded habitats, nor any difference in AMF root colonization in Microstegium across abiotic gradients, providing no evidence of a role for AMF in Microstegium invasion. However, our results did show a negative relationship between AMF root colonization and Microstegium specific leaf area, which may indicate that AMF can alter plant resource allocation, partly explaining its invasion success.