Plant adaptation to local environment through microbial interactions

Kevin D. Ricks, Program in Ecology, Evolution, and Conservation Biology, University of Illinois at Urbana Champaign, Urbana, IL and Anthony Yannarell, Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL

Background/Question/Methods
Plant local adaption is ubiquitous and may be assumed to be the result solely of a plant’s own activities and traits. However, plant roots are colonized by diverse communities of soil microorganisms, which can influence plant fitness and phenotype. Consequently, these plant-microbe interactions may be significant contributors to plant local adaptation. To address this hypothesis, we first sampled the seed of Bromus tectorum from a variety of populations, differing in their soil salinities. As soil salinity is a significant stress and may acts as a strong selective agent on plants, we assumed that these populations were locally adapted to their salinity environment. We then grew these populations in the greenhouse under high or low salinity conditions, and either with or without access to soil microbial partners (live vs. sterile soil). Consequently, comparisons between live and sterile treatments would indicate the degree of plant local adaptation to their respective salinity environment can be mediated through plant-microbial interactions.
Results/Conclusions
We found that populations of Bromus tectorum had the highest benefit from microbial interactions under salinity conditions similar to each population’s home environment. For example, under highly saline conditions, microbial interactions increased saline-adapted populations significantly more that nonsaline-adapted populations. Similarly, under nonsaline conditions, microbial interactions increased nonsaline-adapted populations significantly more that saline-adapted populations. These results persisted as long as a live microbial inoculum was provided. These results suggest that the environment selects for plant root traits associated with adaptive microbe interactions. It is unclear the mechanism by which this adaption takes place. It may be a result of selection for particular root exudate profiles, which produce optimal root microbe communities. Alternatively, it may be the result of selection for an active partner choice by the plant, wherein the plant rewards high quality microbial partners.