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.
Invasive weeds and soil microbes: negative feedback at home and positive feedback away.
Callaway, Ragan*,1, Thelen, Giles1, Holben, William1, 1 Division of Biological Sciences, Missoula, Montana, USA
ABSTRACT- Microbial soil pathogens can regulate plant populations and escape from microbial effects may contribute to the remarkable population explosions of exotics. Soil microbes can also have beneficial effects on plant populations through root-fungus mutualisms and by driving the nutrient cycles on which plants depend. Positive feedbacks occur when plant species accumulate microbes near their roots that have beneficial effects on the plants that cultivate them, and are thought to lead to a loss of community diversity. Negative feedbacks occur when plant species accumulate pathogenic microbes in the soils they occupy which create conditions increasingly hostile to the plants that cultivate them. Negative feedbacks are thought to enhance community diversity by increasing species turnover rates. We compared the effects of soil microbes collected from four populations of Centaurea maculosa L. in its native range in western Europe to the effects of soil microbes collected from five populations in the northwestern U.S. where C. maculosa has invaded. Sterilization of European soils caused a 107% increase in the total biomass of C. maculosa compared to a 29% increase when North American soils were sterilized. In addition, strong feedback loops between soil microbes and C. maculosa were demonstrated. Centaurea maculosa plants grown alone in non-sterile French soil cultured by conspecifics were significantly smaller than those grown in French soils cultured by Festuca ovina. In contrast, C. maculosa planted in Montana soils cultured by conspecifics were significantly larger than in Montana soils cultured by F. idahoensis. Similar results were found for C. maculosa grown in competition with bunchgrasses in cultured French or Montana soils. Sterilization of the soils eliminated these feedbacks. Considered together, these results suggest that C. maculosa is able to modify the microbial community in invaded soils to its own advantage; but not in its native soils.
Key words: plant-soil feedbacks, invasives, soil microbes