Invasive garlic mustard (Alliaria petiolata) alters soil bacterial communities in a northern hardwood forest soil

Garlic mustard (Alliaria petiolata) is a shade-tolerant herb native to Europe that is invading forests in the northern United States.  Garlic mustard displaces native plants and may alter soil microbial communities.  We compared the effects of garlic mustard and two native plants on soil bacterial communities in mature forest remnants in northeastern Ohio.  Soil samples were collected under garlic mustard and the native plants wild leek (Allium tricoccum) and bedstraw (Gallium triflorum).  These plants form discrete patches in mixed mesophytic forest.  Samples were collected with a soil corer to a depth of 5-cm, placed on ice, and subsequently stored at -70C until processed.  DNA was extracted from the soil samples and used to amplify the 16S rRNA gene region using bacterial specific primers.  PCR product was used to generate terminal restriction fragment length polymorphism (TRFLP) profiles of each bacterial community.  Bacterial richness between garlic mustard and the native plants as measured by the number of TRFs (37.1 ± 1.8; 44.6 ± 2.8 respectively) was significantly different (P = 0.041; t = 2.25).  We used multi-response permutation procedures (MRPP) and indicator species analysis to identify differences in bacterial communities among the plant species.  Using MRPP, we found significant differences in the bacterial communities under garlic mustard as compared to wild leek and bedstraw (P = 0.047).  Indicator species analysis showed that certain bacterial groups were significant indicators of either garlic mustard or of native plant species.  These results suggest that garlic mustard alters soil bacterial communities in mature mesophytic forest.