It is well known that soil communities associated with specific plant species affect individual plants’ growth and competitive ability. There is limited evidence that unique soil communities can also differentially influence growth and competition at the ecotype level. Previous work with Arabidopsis thaliana has shown that ecotypes produce distinct and reproducible rhizosphere bacterial communities, with significant differences in both species composition and relative abundance. We tested the hypothesis that these rhizobacterial communities uniquely affect the growth and reproduction of the plant ecotypes with which they are associated. Specifically, we examined the growth of four ecotypes when exposed to their own rhizobacterial communities and the communities generated by each of the other three ecotypes. To do this we planted focal ecotypes inside a ring of six plants that created a “background” soil community. We grew focal plants in this design in three separate soil treatments: non-sterile soil, sterilized soil, and “preconditioned” soil. We preconditioned soil by growing ecotypes in non-sterile soil for six weeks before the start of the experiment. The main experiment was harvested after seven weeks of growth and we recorded height, silique number, and dry weight of each focal plant.

Results/Conclusions

Plants grown in the preconditioned soil treatment showed significantly less growth relative to the non-sterile and sterile soil treatments. In addition, plants in the sterile soil grew significantly larger than those in non-sterile soil. However, we saw no significant interaction between soil treatment and background species. We conclude that the microbial communities have a net negative impact on plant growth, and that the unique bacterial communities associated with each ecotype do not differentially affect plant growth or competition.