Microbial Role of Plant-Soil Negative Feedback Processes and Implications for Weed Management.

Soil microorganisms influence plant germination, growth, and fitness in positive, neutral, or negative ways. Greater understanding of the microbial mechanisms responsible for plant-soil negative feedback could provide new strategies for weed management. We will discuss an ongoing study to uncover microbially produced compounds associated with feedback processes in soil that negatively impact ragweed growth and fitness. We examined the level of microbially-mediated growth suppression of ragweed across multiple sites and focused on specific microbial communities for production of growth inhibiting compounds. We found that activity-based screening of soil metagenomic libraries allows for the isolation of small molecules produced in vector-host expression systems containing large insert DNA fragments extracted from ragweed rhizospheres. Also, we will report on preliminary results featuring batch cultivation of microorganisms derived from soils indicating negative feedback with ragweed. Compound mixtures produced from microbial communities, as opposed to single strains, could reveal novel community-level strategies in microbial suppression of weeds.