The Invasive Legume, Lespedeza Cuneata, Alters Soil Microbial Communities in Heavily Invaded Stands.

Interactions with soil microorganisms may contribute to the success of invasive plants. The invasive legume, Lespedeza cuneata, has spread throughout much of the eastern United States, reducing native plant diversity. The aim of this work was to characterize the impact of L. cuneata on soil bacterial and fungal communities at multiple scales of investigation.  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 three areas: high, low, and no density of L. cuneata. 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.  Bacterial and fungal communities showed similar patterns of variation in our sample set. Overall, the plant species was the greatest influence on microbial community composition, but this was largely due to unique microbial communities found in the root zones of native legumes in areas free of L. cuneata. Microbial communities from the root zones of L. cuneata were 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).  While L. cuneata has a limited influence on soil microbial communities at the scale of individual plants, 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.