Wednesday, November 15, 2006

Possible Shifts of Microbial Community Structure in Temperate Forests of Central Illinois: The Adverse Effects of an Invasive Species, Alliaria petiolata on Pine Plantation stands.

Leah Barth1, Dan Dreager1, Ken Kitchell1, Heather Milligan1, Sam Fan1, Kelly McConnaughay1, and Sherri Morris2. (1) Biology Department, Bradley University, 1501 West Bradley Ave., Peoria, IL 61625, (2) Michigan State University, Biology Dept. Bradley Univ., 1501 West Bradley Ave., Peoria, IL 61625



Previous studies have determined that introduced plant species can alter microbial community dynamics.  This studied evaluated the impacts of a severe infestation of an invasive species, Alliaria petiolata, on microbial community dynamics in a forest soil. We sampled areas of infestation vs. non-infestation within a sand prairie pine plantation in central Illinois using several techniques to evaluate bacterial activity. In situ measurements of total soil respiration showed significant increases in CO2 efflux for infested sites.  In vitro, carbon mineralization was evaluated on unamended and amended garlic mustard and non garlic mustard soils. These soils were exposed to 12 different carbon/nitrogen treatments over 20 days and resulted in a 2-fold increase in the output of CO2 for infested soils treated with glucose and a nitrogen source. Nitrogen mineralization rates were evaluated using thirty-two day incubations.  There were significant increases in nitrification in infested soils. Microbial community dynamics were further evaluated by inoculating soil slurries on non-selective nutrient agar plates and nitrogen free selective agar plates. Direct counts of colonies on selective plates revealed an almost ten-fold increase in bacteria for infested soils. These studies suggest that Alliaria petiolata infestations shift microbial community structure by increasing the population of free-living nitrogen fixing bacteria.  As garlic mustard is currently invading forests at high rates there is a concern that changes in microbial community structure will alter nutrient availability or competitive dynamics of aboveground biomass and alter nutrient dynamics of North American forests.