Anna Truszczynski

THE EFFECT OF CO-EVOLVED MICROBIAL COMMUNITIES ON INVASIVE SPECIES. Anna Truszczynski¹, Laura Beaton¹, Tiffany Knight¹, Biology Department, Washington University in St. Louis, MO^1.

The mechanisms behind the spread of invasive species are not well understood; however, it has been suggested that allelopathy may play a role in the prolific spread of these species. I looked at the possibility that invaders escape from a co-evolved microbial community. This microbial community degrades the allelopathic compounds released by some plants. In a new, naïve microbial community, the allelopathic compounds may be allowed to accumulate in the soil, giving the invaders a competitive edge and allowing them to take over the native plant’s habitat.

Here we look at the impact of the soil microbial community on allelopathy by looking at pairs of closely related native and invasive species: Alliaria petiolata and Erysimum capitatum; Lespedeza cuneata and L. virginica; Rosa multiflora and R. carolina; and Lonicera japonica, L. maackii, L. prolifera, and Symphoricarpos orbiculatus. Plant tissue and soil samples were collected from each species. Iceberg lettuce seeds (Lactuca sativa) were germinated in Petri dishes that contained one of three plant treatments (invasive plant tissue, native plant tissue, no plant tissue) and one of three soil treatments (abiotic, biotic, no soil). The root length and number of germinating seeds were used as a measure of performance to assess allelopathy.

In three of the four plant pairs studied, the tissues of the exotic species were shown to be more toxic than the tissues of the native species, supporting the theory that the success of some invasive species can be related to increased allelopathy. The effect of the soil microbial community on the allelopathy of plant species was inconsistent. For the Rosa plant pair, the allelopathy of the invasive decreased, while the allelopathy of the native was unaffected. For the Lespedeza plant pair, the allelopathy of the invasive was unaffected by the soil microbial community, while the native’s allelopathy decreased. For the Brassicaceae plant pair, the soil microbial community decreased allelopathy for both the native and the invasive species. For the Lonicera plant pair, the allelopathy of the two invasive species decreased while the allelopathy of one native species increased and the allelopathy of another native species was unaffected. This indicates that the escape from a co-evolved microbial community might facilitate the spread of some, but not all invasive species.