Soil Bacterial Community Associations and Functional Potential in a GxE Switchgrass (Panicum virgatum) Experiment

Plant fitness and productivity are largely driven by a combination of adaptive genetic traits and the environment (both climatic and edaphic) in which the plants are grown. Local soil bacterial communities play a role in determining plant nutrient availability and may differentially associate with plants according to variations in morphology and/or root metabolite exudation. The work presented here is part of a large, multi-institutional, multi-year, collaborative project focused on characterizing potential mechanisms of variation in growth and biomass yield of multiple switchgrass (Panicum virgatum) cultivars originating from different climatic regions in North America and planted along a latitudinal gradient. Switchgrass has been extensively studied for its potential use as a bioenergy crop and understanding the factors which govern its productivity in different environments are fundamental to this effort. Our research specifically focuses on the belowground processes regulated by soil microorganisms (e.g., soil organic matter [SOM] decomposition and nitrogen [N] cycling) and aims to identify plant-microbe associations and characterize site-specific edaphic factors which may impact plant nutrient availability and thus growth. Thirty 6m x 6m switchgrass stands (5 replicates of 6 cultivars) were established at each of three sites (Temple, TX; Columbia, MO; and Fermilab, IL) in 2016. The selected cultivars cover a range of genetic diversity in switchgrass, including two lowland ecotypes (Alamo and Kanlow), two upland ecotypes (Blackwell and Cave-In Rock), and two mixed ecotypes (Liberty and Carthage). Soil samples were taken in 2016 before switchgrass planting, and at multiple time-points throughout the 2018 and 2019 growing seasons. DNA was extracted from soils taken next to plant crowns and 16S rRNA amplicon sequencing was performed to determine bacterial community structure. Additionally, we used a combination of qPCR analysis and enzyme assays to investigate the functional dynamics of soil N transformations and extracellular enzyme potential. Preliminary results suggest site related differences in soil bacterial communities and functional potential are likely to exist, however plant associated differences are as yet unknown and will be explored further in the coming months.