Invasive legume, Lespedeza cuneata, alters soil microbial communities in heavily invaded stands

Background/Question/Methods   Interactions with soil microorganisms may contribute to the success of invasive plants, or they may explain some of the detrimental effects that invaders have on native flora. The invasive legume, Lespedeza cuneata, has spread throughout much of the eastern United States, and it has been shown to have a number of microbial associates, including mycorrhizal fungi and nitrogen-fixing rhizobacteria. To explore potential relationships between L. cuneata and soil microbial communities, we sampled the root zones of L. cuneata, native legumes, and bulk soil from natural areas of five military installations throughout the invaded range. At each installation, collections were made in areas without L. cuneata and in areas with high and low densities of L. cuneata. From each sample, we extracted bulk DNA and used a PCR-based, whole community “fingerprinting” analysis to characterize bacterial and fungal communities. We used multivariate data analyses and a variance partitioning scheme to characterize patterns of bacterial and fungal species turnover

Results/Conclusions   Bacterial and fungal communities showed similar patterns of variation in our sample set. Overall, the plant species from which samples derived was the greatest influence on microbial community composition. However, this variation was largely due to unique microbial communities found in the root zones of native legumes from areas free of L. cuneata. Microbial communities from the root zones of L. cuneata were generally not statistically different from those of bulk soil or of co-occurring plants. However, sites with high densities of L. cuneata had microbial communities that were statistically distinct (p = 0.005) from sites with no or low densities of L. cuneata. This effect was consistent across the entire sampled range (i.e. independent of geographical differences). These results suggest that L. cuneata has a limited influence on soil microbial communities at the scale of individual plants, but it may exert a large influence on the local microbial species pool once it attains dominance at a site. This site-scale effect may feed back to plant fitness or to competitive interactions between L. cuneata and native legumes.