PARENT SESSION
Symposium 19: The Role of Plant-Microbe Feedbacks in Plant Invasions
Organized by: K Reinhart and R Callaway
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Oglethorpe Auditorium.

Interactions of exotic species with rhizosphere microbial communities and consequences for nitrogen cycling.

Hawkes, Christine^{*,1, 2, 3}, Firestone, Mary¹, D'Antonio, Carla², ¹ Dept. Environmental Studies, Policy, & Management, Berkeley, CA, US² Dept. Integrative Biology, Berkeley, CA, US³ Dept. Biology, York, UK

ABSTRACT- The success of exotic plant invasions and their subsequent impact on ecosystems may be mediated by interactions with belowground microbial and mycorrhizal communities. We used a combination of DNA-based characterization and ¹⁵N pool dilution to link changes in plant and mycorrhizal communities with changes in nitrogen cycling. In a California grassland, small alterations of mycorrhizal community composition with exotic grass invasion (Avena barbata, Bromus hordeaceus) affected nitrogen cycling, with depressed rates of gross mineralization and nitrification when mycorrhizae of exotic grasses were present. In a semi-arid grassland in Utah, mycorrhizal communities of native grass roots shifted dramatically after cheatgrass (Bromus tectorum) invasion and were correlated with known differences in nitrogen cycling. Mycorrhizae can alter nitrogen cycling either directly or through effects on bacterial community composition and function; we are in the process of quantifying changes to functional genes involved in nitrification to explore the latter at the California site. We have demonstrated that plant invasions can transform belowground microbial and mycorrhizal communities with consequences for ecosystem processes. The success of exotic plant species in novel habitats may be related to their ability to use or manipulate belowground associations and alter the ecosystem to the disadvantage of natives. A better understanding of plant-microbe interactions may facilitate strategies for both invasion prevention and site restoration.

Key words: plant invasion, arbuscular mycorrhizae