INVESTIGATING THE ROLE OF MICROBIAL COMMUNITY COMPOSITION IN SOIL FORMATION WITHIN THE CRITICAL ZONE

Microbes are vital for driving a variety of weathering processes, either directly or indirectly through their activities. Soil samples were collected across a shale climate gradient in North America and Australia to identify microbial community composition with depth and quantify potential microbial community changes in response to resource availability. Soil cores were collected from surface to bedrock on the ridgetop of each site. The cores were evaluated for geochemistry, mineralogy and physical properties, and compared across sites. To analyze microbial composition with depth, 1.5 m deep pits were dug and samples were collected in each horizon while maintaining a clean and sterile environment by wearing nitrile gloves and sterilizing all tools and sampling tubes with ethanol. The samples were preserved with LifeGuard® Soil Preservation Solution and kept frozen. DNA was extracted using PowerSoil DNA Isolation Kits and sent for DNA sequence analysis (16S rRNA amplicon sequencing) followed by PERMANOVA to check for significant differences between sites and depths. Initial findings show that soils are deeper and more weathered in warmer and wetter climates, yet microbial communities are not substantially different between North American sites. Furthermore, microbial communities were also not statistically different with depth at any site despite changes in geochemistry. Microbial communities in Australian shale soils with eucalyptus vegetation, however, are different to North American soils with mixed deciduous forest vegetation. Additional analysis using detailed geochemical data may help determine which environmental factors might control microbial community populations at each site. Quantifying weathering rates and microbial composition will expand our understanding of how different climates are impacting shale soil formation and how microbial composition at depth may influence weathering rates.