The microbial ecology of plant-soil feedback: Exploring the relationship between a microbe's plant preference and its feedback potential

Background/Question/Methods

Plant-soil feedback refers to a general suite of interactions between soil microorganisms and plants: a plant alters the composition or functioning of soil microbial communities, and these microbial changes, in turn, affect the fitness of the plant or its neighbors. A mechanistic understanding of the microbial ecology behind plant-soil feedback requires information about the role of individual microbial taxa in these interactions, but much current research treats microbial communities as "black boxes" or focuses on a few well-characterized microbial groups (e.g. AMF, Rhizobium). Here we cast a wider net. Using empirical data from a series of "home" vs. "away" experiments involving common sunflower and giant ragweed, we characterized over 600 bacterial and fungal taxa as individual agents of feedback. We used Redundancy Analysis to score each microbial taxon according to an index of preference for ragweed or sunflower, and we used Partial Least Squares Regression to quantify the positive or negative feedback potential of each microbial taxon to the growth of the plants. We explored the relationship between preference and feedback potential using linear regression.

Results/Conclusions

"Home" vs. "away" experiments were conducted separately in MI, IL, KS, SD, and OR, and overall microbial community composition was significantly different in each of these trials (p < 0.001). Thus, plants were exposed to multiple distinct microbial species pools from which feedback could result. In spite of this variation in microbial species pools, we found significant (p < 0.001) relationships between microbial preference and feedback potential in 75% of cases. Across all states, bacteria and fungi with a high preference for ragweed tended to reduce ragweed biomass (i.e. negative feedback potential), while those with a high preference for sunflower tended to increase ragweed biomass. Microbes with a preference for sunflower increased sunflower biomass in half of the trials, while they decreased sunflower biomass in the other trials. Thus, ragweed appears to generally attract microbes with negative feedback potential, while sunflower may attract either positive or negative microbes, depending on the particular species pool. We propose that this microbe-centered approach to plant-soil feedback has a great potential to uncover a number of heretofore unknown relationships between plants and soil microorganisms.